680,204 research outputs found
Parton recombination effect in polarized parton distributions
Parton recombination corrections to the standard spin-dependent
Altarelli-Parisi evolution equation are considered in a nonlinear evolution
equation. The properties of this recombination equation and its relation with
the spin-averaged form are discussed.Comment: 25 pages, 1 figure, to be published in Nucl. Phys. B. Appendix is
correcte
Precision Crystal Calorimetry in High Energy Physics
Crystal Calorimetry is widely used in high energy physics because of its
precision. Recent development in crystal technology identified two key issues
to reach and maintain crystal precision: light response uniformity and
calibration in situ. Crystal radiation damage is understood. While the damage
in alkali halides is found to be caused by the oxygen/hydroxyl contamination,
it is the structure defects, such as oxygen vacancies, cause damage in oxides.Comment: 8 pages with 13 eps Figures, RevTe
Game Theory Meets Network Security: A Tutorial at ACM CCS
The increasingly pervasive connectivity of today's information systems brings
up new challenges to security. Traditional security has accomplished a long way
toward protecting well-defined goals such as confidentiality, integrity,
availability, and authenticity. However, with the growing sophistication of the
attacks and the complexity of the system, the protection using traditional
methods could be cost-prohibitive. A new perspective and a new theoretical
foundation are needed to understand security from a strategic and
decision-making perspective. Game theory provides a natural framework to
capture the adversarial and defensive interactions between an attacker and a
defender. It provides a quantitative assessment of security, prediction of
security outcomes, and a mechanism design tool that can enable
security-by-design and reverse the attacker's advantage. This tutorial provides
an overview of diverse methodologies from game theory that includes games of
incomplete information, dynamic games, mechanism design theory to offer a
modern theoretic underpinning of a science of cybersecurity. The tutorial will
also discuss open problems and research challenges that the CCS community can
address and contribute with an objective to build a multidisciplinary bridge
between cybersecurity, economics, game and decision theory
Electrochemical growth of three-dimensionally ordered macroporous metals as photonic crystals
Over the last two decades three dimensionally ordered macroporous (3-DOM) materials have turned out to be very promising in many applications ranging from optics, plasmonics, to catalyst scaffolds. The thesis presents a systematic study on formation and characterisation of 3-DOM metals as photonic crystals. Metals are nearly perfect reflectors with low adsorption at microwave or millimetre wavelengths. Meanwhile they generally absorb visible light because of their negative imaginary part of the dielectric constant that could destroy the band gap in the visible though they. Howevers, for noble metals such as gold, silver and copper, considering the Drude-like behaviour, the adsorption will be small enough to achieve a complete photonic band gap for optical or even shorter wavelengths, with silver performing the best.
In order to fabricate the 3-DOM metallic nanostructures, template-directed electrochemical deposition has been employed in which, initially a highly ordered film of submircon sized colloidal spheres is deposited on to electronically conducting substrates, for instance, indium-tin oxide (ITO) coated glass substrate, through evaporation-induced self-assembly; and subsequently it is infiltrated with metallic elements electrochemically reduced from corresponding electrolytes; fiannly removal of the colloidal templating film reveals a metallic film comprised of periodically arranged spherical voids. Field Emission Gun Scanning Electron Microscopy (FEGSEM) was used to examine the surface morphology and periodicity of the 3-DOM metallic films. It revealed that highly ordered structures are homogenous and uniform over a large scale for both the original colloidal templates and
metallic inverse structures. However for silver electroplated from either silver thiosulfate or silver chlorate bath, voids in the template are fully infiltrated, including both the interstitial spaces between the colloidal spheres and any cracks between film domains, forming a complete solid network over large length scales; for copper the filling factors are strongly dependent on the bath chemistry and in copper sulfate bath isolated macroporous domains can be formed due to those in the cracks will be dissolved back to the solution while those reduced from copper glycerol bath resulted in fully infiltrated structures. Moreover, angle-resolved reflectance spectroscopy has further confirmed the three-dimensional periodicity and indicated the inverse structures have stop band properties in the visible wavelength region, consistent with variation in the effective refractive index of the films.
In addition, surface enhanced Raman scattering (SERS) spectroscopy has been used to evaluate applications of the inverse metals as SERS-active substrates. SERS has nearly exclusively been associated with three noble metals copper, silver (by far the most important) and gold. The 3-DOM metallic thin films possess excellent features for SERS detection arising from their long range periodical void geometry, which gives significant enhancement to Raman intensity. Preliminary measurements have demonstrated the 3-DOM metallic structures are well suited for SERS enhancement. Series spectra from different points of each specimen have given reproducible intensities. Variables associated with Raman intensity such as pore size, dye concentration, and film thickness, have been tuned to achieve maximal enhancement for visible and near-IR wavelengths
Coherence scale of coupled Anderson impurities
For two coupled Anderson impurities, two energy scales are present to
characterize the evolution from local moment state of the impurities to either
of the inter-impurity singlet or the Kondo singlet ground states. The high
energy scale is found to deviate from the single-ion Kondo temperature and
rather scales as Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction when it
becomes dominant. We find that the scaling behavior and the associated physical
properties of this scale are consistent with those of a coherence scale defined
in heavy fermion systems.Comment: 10 pages, 7 figures, extended versio
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