Change search
Refine search result
571572573574575576577 28651 - 28700 of 29271
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 28651.
    Zhang, Ge
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
    Fischer Hübner, Simone
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science. Karlstad University, Faculty of Economic Sciences, Communication and IT, Centre for HumanIT.
    Pallares, Jordi Jaen
    Rebahi, Yacine
    SIP Proxies: New Reflectors? Attacks and Defenses2010Conference paper (Refereed)
    Abstract

    To mitigate identity theft in SIP networks, an inter-domain authentication mechanism based on certificates is proposed in RFC 4474 [10]. Unfortunately, the design of the certificate distribution in this mechanism yields some vulnerabilities. In this paper, we investigate an attack which exploits SIP infrastructures as reflectors to bring down a web server. Our experiments demonstrate that the attacks can be easily mounted. Finally, we discuss some potential methods to prevent this vulnerability

  • 28652.
    Zhang, Ge
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
    Fischer-Huebner, Simone
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science. Karlstad University, Faculty of Economic Sciences, Communication and IT, Centre for HumanIT.
    Detecting Near-Duplicate SPITs in Voice Mailboxes Using Hashes2011In: Proceedings of the 14th international conference on Information security ISC'11, Berlin: Springer Berlin/Heidelberg, 2011, p. 152-167Conference paper (Refereed)
    Abstract [en]

    Spam over Internet Telephony (SPIT) is a threat to the use of Voice of IP (VoIP) systems. One kind of SPIT can make unsolicited bulk calls to victims' voice mailboxes and then send them a prepared audio message. We detect this threat within a collaborative detection framework by comparing unknown VoIP flows with known SPIT samples since the same audio message generates VoIP flows with the same flow patterns (e.g., the sequence of packet sizes). In practice, however, these patterns are not exactly identical: (1) a VoIP flow may be unexpectedly altered by network impairments (e.g., delay jitter and packet loss); and (2) a sophisticated SPITer may dynamically generate each flow. For example, the SPITer employs a Text-To-Speech (TTS) synthesis engine to generate a speech audio instead of using a pre-recorded one. Thus, we measure the similarity among flows using local-sensitive hash algorithms. A close distance between the hash digest of flow x and a known SPIT suggests that flow x probably belongs the same bulk of the known SPIT. Finally, we also experimentally study the detection performance of the hash algorithms

  • 28653.
    Zhang, Ge
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
    Fischer-Huebner, Simone
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science. Karlstad University, Faculty of Economic Sciences, Communication and IT, Centre for HumanIT.
    Timing Attacks on PIN Input in VoIP Networks: Short paper2011In: Detection of Intrusions and Malware, and Vulnerability Assessment: 8th International Conference, DIMVA 2011 / [ed] Holz, Thorsten; Bos, Herbert, Berlin: Springer Berlin/Heidelberg, 2011, p. 75-84Conference paper (Refereed)
    Abstract [en]

    To access automated voice services, Voice over IP (VoIP) users sometimes are required to provide their Personal Identification Numbers (PIN) for authentication. Therefore when they enter PINs, their user-agents generate packets for each key pressed and send them immediately over the networks. This paper shows that a malicious intermediary can recover the inter-keystroke time delay for each PIN input even if the standard encryption mechanism has been applied. The inter-keystroke delay can leak information of what has been typed: Our experiments show that the average search space of a brute force attack on PIN can be reduced by around 80%.

  • 28654.
    Zhang, Ge
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
    Fischer-Hübner, Simone
    Karlstad University, Division for Information Technology.
    A survey on anonymous voice over IP communication: attacks and defenses2014In: Electronic Commerce Research, ISSN 1389-5753, E-ISSN 1572-9362, ISSN 1389-5753Article in journal (Refereed)
  • 28655.
    Zhang, Ge
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
    Fischer-Hübner, Simone
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Counteract DNS Attacks on SIP Proxies Using Bloom Filters2013In: 2013 International Conference on Availability, Reliability and Security, IEEE, 2013, p. 678-684Conference paper (Refereed)
    Abstract [en]

    SIP proxies play an important part in VoIP services. A Denial of Service (DoS) attack on them may cause the failure of the whole network. We investigate such a DoS attack by exploiting DNS queries. A SIP proxy needs to resolve domain names for processing a message. However, a DNS resolution may take a while. To avoid being blocked, a proxy suspends the processing task of the current message during its name resolution, so that it can continue to deal with other messages. Later when the answer is received, the suspended task will be resumed. It is an asynchronous implementation of DNS queries. Unfortunately, this implementation consumes memory storage and also brings troubles like a race condition. An attacker can collect a list of domain names which take seconds to resolve. Then, the attacker sends to a victim SIP proxy messages which contain these domain names. As a result, the victim proxy has to suspend a number of messages in a short while. Our experiments show that a SIP proxy can be easily crashed by such an attack and thus be not available anymore. To solve the problem, we analyzed the reasons that make a DNS query time-consuming, and then proposed a prevention scheme using bloom filters to blacklist suspicious DNS authoritative servers. Results of our experiments show it efficiently mitigates the attack with a reasonable false positive rate.

  • 28656.
    Zhang, Ge
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
    Fischer-Hübner, Simone
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
    Ehlert, Sven
    Blocking attacks on SIP VoIP proxies caused by external processing2010In: Telecommunications Systems, ISSN 1018-4864, E-ISSN 1572-9451, Vol. 45, no 1, p. 61-76Article in journal (Refereed)
  • 28657.
    Zhang, Ge
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
    Fischer-Hübner, Simone
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
    Martucci, Leonardo A.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
    Ehlert, Sven
    Fraunhofer FOKUS, Berlin, Germany.
    Revealing the calling history on SIP VoIP systems by timing attacks2009In: Proceedings of the 4th International Conference on Availability, Reliability and Security (ARES 2009), IEEE Press, IEEE Computer Society, 2009, p. 135-142Conference paper (Refereed)
    Abstract [en]

    Many emergent security threats which did not exist in the traditional telephony network are introduced in SIP VoIP services. To provide high-level security assurance to SIP VoIP services, an inter-domain authentication mechanism is defined in RFC 4474. However, this mechanism introduces another vulnerability: a timing attack which can be used for effectively revealing the calling history of a group of VoIP users. The idea here is to exploit the certificate cache mechanisms supported by SIP VoIP infrastructures, in which the certificate from a caller's domain will be cached by the callee's proxy to accelerate subsequent requests. Therefore, SIP processing time varies depending whether the two domains had been into contact beforehand or not. The attacker can thus profile the calling history of a SIP domain by sending probing requests and observing the time required for processing. The result of our experiments demonstrates that this attack can be easily launched. We also discuss countermeasures to prevent such attacks

  • 28658.
    Zhang, Ge
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
    Pallares, Jordi Jaen
    Rebahi, Yacine
    Fischer-Hübner, Simone
    Karlstad University, Division for Information Technology.
    SIP Proxies: New Reflectors in the Internet2010In: Communications and Multimedia Security: 11th IFIP TC 6/TC 11 International Conference, CMS 2010, Linz, Austria, May 31 – June 2, 2010. Proceedings, Springer, 2010, p. 142-153Conference paper (Refereed)
    Abstract [en]

    To mitigate identity theft in SIP networks, an inter-domain authentication mechanism based on certificates is proposed in RFC 4474 [10]. Unfortunately, the design of the certificate distribution in this mechanism yields some vulnerabilities. In this paper, we investigate an attack which exploits SIP infrastructures as reflectors to bring down a web server. Our experiments demonstrate that the attacks can be easily mounted. Finally, we discuss some potential methods to prevent this vulnerability.

  • 28659.
    Zhang, Ge
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
    Rebahi, Yacine
    Side effects of identity management in SIP VoIP environment2011In: Information Security Technical Report, ISSN 1363-4127, Vol. 16, no 1, p. 29-35Article in journal (Refereed)
    Abstract [en]

    In this article, we summarize the security threats targeting SIP proxy servers or other infrastructures in NGN by misusing a specific signaling authentication mechanism, which has been proposed in RFC 4474 (Peterson and Jennings, 2006). This mechanism is designed to authenticate inter-domain SIP requests based on domain certificates to prevent identity theft. Nevertheless, despite its contribution, this protection raises some “side effects”, that actually lead to new vulnerabilities in both the availability and confidentiality of SIP services. We provide an overview of different attack possibilities and explain them in more detail, including attacks utilizing algorithm complexity, certificates storage, and certificates distribution. We also suggest some alternative design to prevent or reduce the attacks. SIP, VoIP, NGN, Authentication, Denial of Service, Timing attack.

  • 28660.
    Zhang, Ge
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
    Rebahi, Yacine
    Tuan Minh, Nguyen
    Performance Analysis of Identity Management in the Session Initiation protocol (SIP)2009In: Communications of the ACS, ISSN 2090-102X, Vol. 2, no 001Article in journal (Refereed)
    Abstract [en]

    The Session Initiation Protocol (SIP) is a standard for managing IP multimedia sessions in the Internet. Identity management in SIP is a crucial security field that deals with identifying users in SIP networks and controlling their access to the corresponding resources. RFC 4474 describes a mechanism, based on certificates, for dealing with the SIP users identities. This RFC recommends the use of the RSA algorithm as it is currently the most popular public key cryptography system. The proliferation of small and simple devices as well as the need to increase the capacity of the SIP servers to handle the increasing VoIP traffic will make continued reliance on RSA more challenging over time. In this paper, we describe our implementation of the current RFC 4474, our integration of elliptic curves cryptography into this RFC and show that the corresponding performance is much more significant than the one where RSA is used. This paper can be considered as a first step in standardizing the use of elliptic curves in the identity management for SIP

  • 28661.
    Zhang, Hanmin
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Adatom-induced metal/semiconductor transitions on Ag/Si(111) and Ag/Ge(111) surfaces2003Conference paper (Refereed)
  • 28662.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Balasubramanian, T.
    Uhrberg,, R. I. G.
    Core-level photoelectron spectroscopy study of the Au/Si(111) 5×2,  α−3  √ ×3  √ ,  β−3  √ ×3  √ ,  and 6×6  surfaces2001In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Phys. Rev. B 65, 035314 (2001), Vol. 65, no 3Article in journal (Refereed)
  • 28663.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Balasubramanian, T.
    Uhrberg,, R. I. G.
    Metal to semiconductor transition on Ag/Ge(111): surface electronic structure of the √3 × √3, √39 × √39  and 6x6 surfaces2001In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 63, no 19Article in journal (Refereed)
  • 28664.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Balasubramanian, T.
    Uhrberg,, R. I. G.
    Surface electronic structure of the √3 × √3, √39 × √39 and 6 × 6 surfaces of Ag/Ge(111): observation of a metal to semiconductor transition2000Conference paper (Refereed)
  • 28665.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Balasubramanian, T.
    Uhrberg,, R. I. G.
    Surface electronic structure of the √3 × √3, √39 × √39 and 6 × 6 surfaces of Ag/Ge(111): observation of a metal to semiconductor transition2001In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 175, p. 237-242Article in journal (Refereed)
  • 28666.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Balasubramanian, T.
    Uhrberg,, R. I. G.
    Surface electronic structure study of Au/Si(111) reconstructions: Observation of a crystal to glass transition2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 16Article in journal (Refereed)
  • 28667.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Balasubramanian, T.
    Uhrberg, R.I.G.
    Comparative Study of the Electron Structure of Sn/Ge(111) and Sn/Si(111): Indications of a Low Temperature Phase Transition2000Conference paper (Refereed)
  • 28668.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Balasubramanian, T.
    Uhrberg, R.I.G.
    Photoelectron Spectroscopy of the 5x2, alpha-√3 × √3, beta-√3 × √3, and 6x6 phases of Au/Si(111)2000Conference paper (Refereed)
  • 28669.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Ericsson, Leif
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Photoemission and NEXAFS Studies of PTCDA on Sn/Si(111)2√3x2√32010Conference paper (Other academic)
  • 28670.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Ericsson, Leif
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    PTCDA induced reconstruction on Sn/Si(111)-2√3×2√32012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 24, p. 245317-1-245317-5Article in journal (Refereed)
    Abstract [en]

    The electronic structures of the Sn/Si(111)-2√3×2√3 surface and deposited 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) have been studied by use of high-resolution photoelectron spectroscopy and scanning tunneling microscopy. On deposition, PTCDA molecules form a 4√3×2√3 periodicity superposed on the substrate. The new reconstruction is caused by a charge transfer between the Sn/Si(111)-2√3×2√3 surface and the molecules, as indicated by a new component of the Sn 4d core level that is shifted toward higher binding energy. In contrast to earlier reports, the charge provided by Sn is given to carbonyl C atoms instead of O atoms. This is evidenced by a new component in the C 1s core-level spectra, which is shifted toward lower binding energy. The charge transfer also induces a splitting in the highest occupied molecular orbital level of PTCDA seen in the valence band structure.

  • 28671.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Ericsson, Leif
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    PTCDA on Sn/Si(111)-2√3×2√32012Conference paper (Refereed)
  • 28672.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Gustafsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Electronic structure of PTCDA on Sn/Si(111)-√3×√32011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, ISSN ISSN 1550-235x (online), 1098-0121 (print), Vol. 84, no 20, p. 205420-1-205420-8Article in journal (Refereed)
    Abstract [en]

    The electronic structures of PTCDA films on Sn/Si(111)-√3×√3 have been studied by high-resolution photoelectron spectroscopy (PES) and near-edge x-ray absorption fine structure (NEXAFS). There is a clear chemical interaction between PTCDA molecules and the Sn/Si(111)-√3×√3 surface, as indicated by new components in Sn 4d core levels that are shifted to higher binding energies. The chemical interaction is also evidenced by new components in the O-1s and C-1s core-level spectra. The new components are shifted to lower binding energies and have their origins from two reactions between Sn dangling bonds and the PTCDA molecules. One reaction is located at the anhydride O atom and the other is at the carbonyl C atom. These reactions also induce modifications in the HOMO and LUMO levels seen in the valence band and NEXAFS spectra. For thin films, the NEXAFS results suggest a tilting molecular configuration with respect to the substrate, while for the thicker films, there is an improved ordering of the molecular orientation to the substrate.

  • 28673.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Gustafsson, Jörgen
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Electronic Structure Studies of PTCDA on Ag/Si(111)-sqrt3xsqrt32007Conference paper (Refereed)
  • 28674.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Gustafsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Photoemission and NEXAFS Studies of PTCDA on Sn/Si(111)√3x√32009Conference paper (Refereed)
  • 28675.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Gustafsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    STM study of the electronic structure of PTCDA on Ag/Si(111)-√3×√32010In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 485, no 1-3, p. 69-76Article in journal (Refereed)
    Abstract [en]

    PTCDA molecules were evaporated onto the Ag/Si(111)-√3×√3 surface. Simple HOMO and LUMO models have been made to explain the STM images of the square and herringbone phases. The charge transfer from the substrate and the H-bonding between the molecules play crucial roles for the formation of these phases. We found that their electronic structures are strongly modified by the moleculesubstrate and intermolecular interactions. As a result, the HOMO-LUMO gaps of the PTCDA films are different for different phases and thicknesses. The increase in the HOMO-LUMO gaps with film thicknesses is discussed based on the surface and the interface polarization effect

  • 28676.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Gustafsson, Jörgen
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Surface atomic structure of Ag/Si(111)√3 × √32006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 20Article in journal (Refereed)
  • 28677.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Gustafsson, Jörgen
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    The tip role on STM images of Ag/Si(111)√3 × √32007In: Journal of Physics: Conference Series, ISSN 1742-6596, Vol. 61, no 1Article in journal (Refereed)
  • 28678.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Gustafsson, Jörgen
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    The tip role on STM images of Ag/Si(111)√3 × √32006Conference paper (Refereed)
  • 28679.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Hirvonen Grytzelius, Joakim
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Electronic structure of Mn/Ge(111)-√3×√3 thin films studied by photoelectron spectroscopy2009Conference paper (Refereed)
  • 28680.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Hirvonen Grytzelius, Joakim
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Johansson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Thin Mn germanide films studied with XPS, STM, and XMCD2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 4, p. 045311-1-045311-6Article in journal (Refereed)
    Abstract [en]

    Thin Mn germanide films with nanoscale thicknesses on Ge(111) have been studied by low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), core-level spectroscopy (CLS), and x-ray magnetic circular dichroism. The 260 C annealing of 16 monolayers of Mn deposited on Ge(111)c(2×8) resulted in a uniform film with intense threefold split √3×√3 LEED spots and Moiré patterns in the STM images. This ultrathin film shows a clear ferromagnetism with a Curie temperature of ∼250 K. High-resolution Ge 3d CLS spectra were recorded with photon energies between 50 and 90 eV at normal and 60 emission angle. To achieve a consistent fit over the energy and angular range three components were used in the line-shape analysis. The low temperature (260 C) annealed film shows significant differences in terms of electronic structure and magnetism in contrast to the high temperature (330 C or above) annealed ones. Our results indicate that the annealing temperature and the Mn coverage play important roles in the formation of a thin magnetic Mn germanide film.

  • 28681.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics. CMM, Characterization and modeling of materials.
    Holleboom, Thijs
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Band splitting of quantum wells of thin Ag films on Sn/Si(111)√3×√32017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 4, p. 041402-1-041402-6Article in journal (Refereed)
    Abstract [en]

    High-resolution valence band spectra of ultrathin Ag films on Sn/Si(111)√3×√3 show intrinsic splitting of the quantum-well states (QWSs). Especially at low coverages, the QWSs of such a system display delicate coupling characters with the bulk bands from the substrate. The observed QWS splitting agrees well with the result of the theoretical calculation. We found that the splitting originates from an interface with a finite thickness. In addition, the interface also causes a large sp band splitting due to the Umklapp scattering in the Γ−M direction of the Ag(111) surface Brillouin zone.

  • 28682.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Jemander, S. T.
    Lin, N.
    Hansson, G. V.
    Uhrberg, R. I. G.
    Origin of 3x3 diffraction on the Sn1-xSix /Si(111)sqrt3xsqrt3 surface2003In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 531, no 1, p. 21-28Article in journal (Refereed)
  • 28683.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Johansson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Electronic structure of PTCDA on Sn/Si(111)-2√3×2√32014In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 439, p. 71-78Article in journal (Refereed)
    Abstract [en]

    The electronic structures of PTCDA on the Sn/Si(111)-2√3×2√3 surface have been thoroughly studied by high-resolution photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS). Upon deposition of PTCDA, there is an unusual charge transfer from the Sn/Si(111)-2√3×2√3 surface to the molecules. This is clearly shown by a new component in the Sn 4d core-level spectra that shifts towards higher binding energy. In contrast to the literature, the charge provided by Sn is donated to the carbonyl C instead of the O atoms. This is revealed by a new component in the C 1s core-level spectra that shifts towards lower binding energy. The charge transfer causes a splitting of the HOMO level in the valence band spectra. As indicated in the NEXAFS spectra, it also induces a splitting of the LUMO level of the molecules. For thick films the NEXAFS results suggest a layer by layer growth mode.

  • 28684.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    STM study of PTCDA on Sn/Si(111)-2 root 3 x 2 root 32016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, no 12, article id 124701Article in journal (Refereed)
    Abstract [en]

    The electronic structures of perylene tetracarboxylic dianhydride on Sn/Si(111)-2 root 3 x 2 root 3 have been studied by scanning tunneling microscopy and spectroscopy. Individual molecules have been investigated at 0.15 ML, while at 0.3 ML molecules formed short rods. At 0.6 ML, the molecular rods interacted with each other, coupling with the substrate and forming a new 4 root 3 x 2 root 3 super structure. At 0.9 ML, the surface was further reconstructed and consisted of strips with two and three rods of molecules. We found that these surface structures are strongly modified by the molecule/substrate and the intermolecular interactions. As a result, the HOMO-LUMO gaps of these molecules change with respect to the phases and the thickness. For a single molecular layer of the 4 root 3 x 2 root 3 phase, the HOMO-LUMO levels were split with a gap of approximately 2.1 eV, which is caused by charge transfer from the substrate to the molecules. (C) 2016 AIP Publishing LLC.

  • 28685.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Sakamoto,, K.
    Uhrberg,, R. I. G.
    Comprehensive study of the metal/semiconductor character of adatom-induced Ag/Si(111) reconstructions2001In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Phys. Rev. B 64, 245421 (2001), Vol. 64, no 24Article in journal (Refereed)
  • 28686.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Sakamoto, K.
    Uhrberg, R. I. G.
    High temperature annealing and surface photovoltage shift on Si(111)7x72008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 3Article in journal (Refereed)
  • 28687.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Sakamoto, K.
    Uhrberg, R. I. G.
    Semiconductor-Metal-Semiconductor Transition: Valence Band Photoemission Study of Ag/Si(111) Surfaces2001Conference paper (Refereed)
  • 28688.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Sakamoto, K.
    Uhrberg, R. I. G.
    Semiconductor-metal-semiconductor transition: valence band photoemission study of Ag/Si(111) surfaces2002In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 190, no 1-4, p. 103-107Article in journal (Refereed)
  • 28689.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Sakamoto, K.
    Uhrberg, R. I. G.
    Surface electronic structure of K and Cs-induced sqrt21xsqrt21 phases on Ag/Si(111)sqrt3xsqrt32004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 24Article in journal (Refereed)
  • 28690.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Sakamoto, K.
    Uhrberg,, R. I. G.
    Surface electronic structures of Au-induced reconstructions on the Ag/Ge(111)-sqrt3xsqrt3 surface2002Conference paper (Refereed)
  • 28691.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Sakamoto, K.
    Uhrberg,, R. I. G.
    Surface electronic structures of Au-induced reconstructions on the Ag/Ge(111)sqrt3xsqrt3 surface2003In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 934, p. 532-535Article in journal (Refereed)
  • 28692.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Sakamoto, Kazuyuki
    Hansson, G.V.
    Uhrberg, R.I.G.
    High temperature annealing and surface photovoltage shifts on Si(111)7x72008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 3Article in journal (Refereed)
  • 28693.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Uhrberg, R. I. G.
    Ag/Si(111)sqrt(3)×sqrt(3): Surface band splitting and the IET-model2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 19-15Article in journal (Refereed)
  • 28694.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Uhrberg,, R. I. G.
    Atomic structures of Ag/Ge(111)sqrt39xsqrt39 and 6x6 surfaces studied by STM: observations of bias dependent reconstruction transformations2003In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Appl. Surf. Sci., 212-213, 353 (2003), Vol. 212-213, p. 353-359Article in journal (Refereed)
  • 28695.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Uhrberg, R. I. G.
    Reinvestigation of the surface state band splitting on Ag/Si(111)sqrt3xsqrt32005Conference paper (Refereed)
  • 28696.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Uhrberg,, R. I. G.
    Surface reconstruction manipulation by STM2004Conference paper (Refereed)
  • 28697.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Uhrberg, R.I.G.
    Direct Manipulation of Surface Reconstructions by STM2002Conference paper (Refereed)
  • 28698.
    Zhang, Hanmin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Uhrberg, R.I.G.
    Scanning Tunneling Microscopy Study of Ag/Ge(111): Observation of Surface Reconstruction Transformations2003In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 546, no 1-2, p. L789-L796Article in journal (Refereed)
  • 28699.
    Zhang, Ke
    Karlstad University, Faculty of Economic Sciences, Communication and IT.
    The Self-identification and Media Literacy Of Middle Class through Media in China: An Empirical Study in Beijing2013Independent thesis Advanced level (degree of Master (Two Years)), 80 credits / 120 HE creditsStudent thesis
  • 28700.
    Zhang, Xiaojing
    et al.
    ABB Corporate Research.
    Lindberg, Therese
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Svensson, Krister
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Vyatkin, Valeriy
    Department of Computer Science, Electrical and Space Engineering at LuleåUniversity of Technology, Sweden and the Department of Electrical Engineering and Automation, Aalto University, Finland.
    Mousavi, Arash
    Department of Computer Science, Electrical and Space Engineering at LuleåUniversity of Technology, Sweden.
    Power Consumption Modeling of Data Center IT Room with Distributed Air Flow2016In: International Journal of Modeling and Optimization, ISSN 2010-3697, Vol. 6, no 1, p. 33-38Article in journal (Refereed)
    Abstract [en]

    Modern data centers are characterized by large sizes, high energy consumption and complexity involving IT, power supply, ventilation and cooling. Data center energy efficiency is a major concern for data center design and operation. To improve data center energy efficiency through efficient cooling and ventilation, advanced process control and optimization, process models to describe the process power consumption are required. In this work, data center power consumption models are investigated. A concept of distributed air flow control is presented. The objective is to develop a comprehensive data center power consumption model to describe IT room, computer room air handling (CRAH), data center ventilation and cooling characteristics as well as distributed air flow control. Data center operation scenarios with uneven IT load are simulated. Results show that the distributed air flow control can save the cooling energy significantly.

571572573574575576577 28651 - 28700 of 29271
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf