248,735 research outputs found
Shot-noise in transport and beam experiments
Consider two Fermi gases with the same {\it average} currents: a transport
gas, as in solid-state experiments where the chemical potentials of terminal 1
is and of terminal 2 and 3 is , and a beam, i.e., electrons
entering only from terminal 1 having energies between and . By
expressing the current noise as a sum over single-particle transitions we show
that the temporal current fluctuations are very different: The beam is noisier
due to allowed single-particle transitions into empty states below .
Surprisingly, the correlations between terminals 2 and 3 are the same.Comment: 4 pages, 2 figure
Epistemic Foundation of Stable Model Semantics
Stable model semantics has become a very popular approach for the management
of negation in logic programming. This approach relies mainly on the closed
world assumption to complete the available knowledge and its formulation has
its basis in the so-called Gelfond-Lifschitz transformation.
The primary goal of this work is to present an alternative and
epistemic-based characterization of stable model semantics, to the
Gelfond-Lifschitz transformation. In particular, we show that stable model
semantics can be defined entirely as an extension of the Kripke-Kleene
semantics. Indeed, we show that the closed world assumption can be seen as an
additional source of `falsehood' to be added cumulatively to the Kripke-Kleene
semantics. Our approach is purely algebraic and can abstract from the
particular formalism of choice as it is based on monotone operators (under the
knowledge order) over bilattices only.Comment: 41 pages. To appear in Theory and Practice of Logic Programming
(TPLP
Role of structural relaxations and vibrational excitations in the high-frequency dynamics of liquids and glasses
We present theoretical investigation on the high-frequency collective
dynamics in liquids and glasses at microscopic length scales and terahertz
frequency region based on the mode-coupling theory for ideal liquid-glass
transition. We focus on recently investigated issues from
inelastic-X-ray-scattering and computer-simulation studies for dynamic
structure factors and longitudinal and transversal current spectra: the
anomalous dispersion of the high-frequency sound velocity and the nature of the
low-frequency excitation called the boson peak. It will be discussed how the
sound mode interferes with other low-lying modes present in the system.
Thereby, we provide a systematic explanation of the anomalous sound-velocity
dispersion in systems -- ranging from high temperature liquid down to deep
inside the glass state -- in terms of the contributions from the
structural-relaxation processes and from vibrational excitations called the
anomalous-oscillation peak (AOP). A possibility of observing negative
dispersion -- the {\em decrease} of the sound velocity upon increase of the
wave number -- is argued when the sound-velocity dispersion is dominated by the
contribution from the vibrational dynamics. We also show that the low-frequency
excitation, observable in both of the glass-state longitudinal and transversal
current spectra at the same resonance frequency, is the manifestation of the
AOP. As a consequence of the presence of the AOP in the transversal current
spectra, it is predicted that the transversal sound velocity also exhibits the
anomalous dispersion. These results of the theory are demonstrated for a model
of the Lennard-Jones system.Comment: 25 pages, 22 figure
Pembuatan detektor Sinar-X Isisan Gas jenis proporsional Tipe Jendela samping
Telah dibuat dan diteliti detektor proporsional tripe jendela samping dengan gas isian argon dan metana Tekanan total gas isian adalah 400 mmHg dengan perbandingan tekanan 95 : 5. Katoda terbuat clari stainless steel berdiameter 24,2 mm dengan panjang 100mm dan anoda dari tungsten berdiameter 0,08 mm. Jendela terbuat dari berilium, dengan panjang 24 mm dan lebar 12 mm.
Dari pengujian detektor diperoleh bahwa tegangan ambang 2200 volt, plats 125 volt, slope 2,3%/100 volt, resolusi energi 11,66 % dan efisiensi 8,57 % terhadap sinar-X dengan somber Fels pada jarak 0 mm. A side window proportional counter has been made and observed. Argon and methane with the total pressure of 400 mmHg and the pressure ratio of 95 ; 5 are used as a filled gas. The cathode with diameter of 24,2 mm, length of 100 mm and anode with diameter of 0,08 mm made of stainless steel and tungsten respectively are used in this experiment. Beryllium with length of 24 mm and width of 12 mm is used as a window.
The performance test of this detector shows that the treshold voltage , plateau, slope, energy resolution and efficiency for X-ray with Fe55 as a radiation source at 0 mm are 2200 volt, 125 volt, 2,3%/100 volt, 11,66 % and 8,57 % respectively
One antimatter --- two possible thermodynamics
Conventional thermodynamics, which is formulated for our world populated by
radiation and matter, can be extended to describe physical properties of
antimatter in two mutually exclusive ways: CP-invariant or CPT-invariant. Here
we refer to invariance of physical laws under charge (C), parity (P) and time
reversal (T) transformations. While in quantum field theory CPT invariance is a
theorem confirmed by experiments, the symmetry principles applied to
macroscopic phenomena or to the whole of the Universe represent only
hypotheses. Since both versions of thermodynamics are different only in their
treatment of antimatter, but are the same in describing our world dominated by
matter, making a clear experimentally justified choice between CP invariance
and CPT invariance in context of thermodynamics is not possible at present.
This work investigates the comparative properties of the CP- and CPT-invariant
extensions of thermodynamics (focusing on the latter, which is less
conventional than the former) and examines conditions under which these
extensions can be experimentally tested.Comment: 20 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1209.198
Yano-Koonin-Podgoretskii Parametrisation of the Hanbury Brown-Twiss Correlator
The Yano-Koonin-Podgoretskii (YKP) parametrisation of Hanbury Brown-Twiss
(HBT) two-particle correlation functions opens new strategies for extracting
the emission duration and testing the longitudinal expansion in heavy-ion
collisions. Based on the recently derived model-independent expressions, we
present a detailed parameter study of the YKP parameters for a finite,
hydrodynamically expanding source model of heavy-ion collisions. For the class
of models studied here, we show that the three YKP radius parameters have an
interpretation as longitudinal extension, transverse extension and emission
duration of the source in the YKP frame. This frame is specified by the fourth
fit parameter, the Yano-Koonin velocity which describes to a good approximation
the velocity of the fluid element with highest emissivity and allows to test
for the longitudinal expansion of the source. Deviations from this
interpretation of the YKP parameters are discussed quantitatively.Comment: 38 pages, REVTeX, 11 PS-figures, to be published in Z.Phys.
Finite-size scaling of helix-coil transitions in poly-alanine studied by multicanonical simulations
We report results from multicanonical simulations of poly-alanine.
Homopolymers of up to 30 amino acids were considered and various thermodynamic
quantities as a function of temperature calculated. We study the nature of the
observed helix-coil transition and present estimates for critical exponents.Comment: to appear in J.Chem.Phys. (Jan 99
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