251 research outputs found
Backflow and dissipation during the quantum decay of a metastable Fermi liquid
The particle current in a metastable Fermi liquid against a first-order phase
transition is calculated at zero temperature. During fluctuations of a droplet
of the stable phase, in accordance with the conservation law, not only does an
unperturbed current arise from the continuity at the boundary, but a backflow
is induced by the density response. Quasiparticles carrying these currents are
scattered by the boundary, yielding a dissipative backflow around the droplet.
An energy of the hydrodynamic mass flow of the liquid and a friction force
exerted on the droplet by the quasiparticles have been obtained in terms of a
potential of their interaction with the droplet.Comment: 5 pages (REVTeX), to be published in Phys. Rev.
Renormalization of hole-hole interaction at decreasing Drude conductivity
The diffusion contribution of the hole-hole interaction to the conductivity
is analyzed in gated GaAs/InGaAs/GaAs heterostructures. We show
that the change of the interaction correction to the conductivity with the
decreasing Drude conductivity results both from the compensation of the singlet
and triplet channels and from the arising prefactor in the
conventional expression for the interaction correction.Comment: 6 pages, 5 figure
A Damping of the de Haas-van Alphen Oscillations in the superconducting state
Deploying a recently developed semiclassical theory of quasiparticles in the
superconducting state we study the de Haas-van Alphen effect. We find that the
oscillations have the same frequency as in the normal state but their amplitude
is reduced. We find an analytic formulae for this damping which is due to
tunnelling between semiclassical quasiparticle orbits comprising both
particle-like and hole-like segments. The quantitative predictions of the
theory are consistent with the available data.Comment: 7 pages, 5 figure
Spin and Charge Correlations in Quantum Dots: An Exact Solution
The inclusion of charging and spin-exchange interactions within the Universal
Hamiltonian description of quantum dots is challenging as it leads to a
non-Abelian action. Here we present an {\it exact} analytical solution of the
probem, in particular, in the vicinity of the Stoner instabilty point. We
calculate several observables, including the tunneling density of states (TDOS)
and the spin susceptibility. Near the instability point the TDOS exhibits a
non-monotonous behavior as function of the tunneling energy, even at
temperatures higher than the exchange energy. Our approach is generalizable to
a broad set of observables, including the a.c. susceptibility and the
absorption spectrum for anisotropic spin interaction. Our results could be
tested in nearly ferromagnetic materials.Comment: JETPL class, 6 pages, 2 figure
Out-of-Equilibrium Admittance of Single Electron Box Under Strong Coulomb Blockade
We study admittance and energy dissipation in an out-of-equlibrium single
electron box. The system consists of a small metallic island coupled to a
massive reservoir via single tunneling junction. The potential of electrons in
the island is controlled by an additional gate electrode. The energy
dissipation is caused by an AC gate voltage. The case of a strong Coulomb
blockade is considered. We focus on the regime when electron coherence can be
neglected but quantum fluctuations of charge are strong due to Coulomb
interaction. We obtain the admittance under the specified conditions. It turns
out that the energy dissipation rate can be expressed via charge relaxation
resistance and renormalized gate capacitance even out of equilibrium. We
suggest the admittance as a tool for a measurement of the bosonic distribution
corresponding collective excitations in the system
The problem of "macroscopic charge quantization" in single-electron devices
In a recent Letter by the authors [I.S. Burmistrov and A.M.M. Pruisken, Phys.
Rev. Lett. 101, 056801 (2008)] it was shown that single-electron devices
(single electron transistor or SET) display "macroscopic charge quantization"
which is completely analogous to the quantum Hall effect observed on very
different electron systems. In this investigation we present more detail on
these new findings. Based on the Ambegaokar-Eckern-Schoen (AES) theory of the
Coulomb blockade we introduce a general response theory that probes the
sensitivity of SET to changes in the boundary conditions. This response theory
defines a new set of physical observables and we establish the contact with the
standard results obtained from ordinary linear response theory. The response
parameters generally define the renormalization behavior of the SET in the
entire regime from weak coupling with large values of the tunneling conductance
all the way down to the strong coupling phase where the system displays the
Coulomb blockade. We introduce a general criterion for charge quantization that
is analogous to the Thouless criterion for Anderson localization. We present
the results of detailed computations on the weak coupling side of the theory,
i.e. both perturbative and non-perturbative (instantons). Based on an effective
theory in terms of quantum spins we study the quantum critical behavior of the
AES model on the strong coupling side. Consequently, a unifying scaling diagram
of the SET is obtained. This diagram displays all the super universal
topological features of the theta-angle concept that previously arose in the
theory of the quantum Hall effect.Comment: RevTex, 22 pages, 10 figure
Charge relaxation resistance in the Coulomb blockade problem
We study the dissipation in a system consisting of a small metallic island
coupled to a gate electrode and to a massive reservoir via single tunneling
junction. The dissipation of energy is caused by a slowly oscillating gate
voltage. We compute it in the regimes of weak and strong Coulomb blockade. We
focus on the regime of not very low temperatures when electron coherence can be
neglected but quantum fluctuations of charge are strong due to Coulomb
interaction. The answers assume a particularly transparent form while expressed
in terms of specially chosen physical observables. We discovered that the
dissipation rate is given by a universal expression in both limiting cases.Comment: 21 pages, 12 figure
Two-dimensional electron liquid with disorder in a weak magnetic field
We present the effective theory for low energy dynamics of a two-dimensional
interacting electrons in the presence of a weak short-range disorder and a weak
perpendicular magnetic field, the filling factor . We investigate
the exchange enhancement of the -factor, the effective mass and the decay
rate of the simplest spin wave excitations at . We obtain the
enhancement of the field-induced gap in the tunneling density of states and
dependence of the tunneling conductivity on the applied bias.Comment: 17 pages, no figure
СИНТЕЗ ТА АНТИБАКТЕРІАЛЬНІ ВЛАСТИВОСТІ 4-АМІНОФЕНІЛСУЛЬФОНАМІДУ, ІММОБІЛІЗОВАНОГО НА ПОЛІМЕРНОМУ НОСІЇ
The aim of the study. Today the immobilization of drugs to the polymeric carriers is increasingly important, due to the requirements to reduce the toxicity and prolongation of action of drugs. It is known the immobilization of the Sulfonamides on the Stiromali, methacrylate polymer matrices, wherein the pharmacologically active sulfanilamide easily remove from the polymer upon the application, by the acid hydrolysis. At the same time it is noted that immobilized sulfonamides derived from aminomethylated Styrene-divinylbenzene copolymer, although hydrolytic stability, maintain the antibacterial properties. In order to expand the examples of covalent immobilization of sulfonamides we synthesized 4-aminophenylsulfonamide on pellet and brous forms of styrene and divinylbenzene with SO2 as a bridging group.Materials and Methods. As a raw materials, we used the pellet macroporous sulfonated Styrene-divinylbenzene copolymer and copolymers Polypropylene and Styrene. Sulfochlorination of these copolymers the polymeric sulfonyl chlorides were obtained. This compounds were used in the reaction with 4-aminophenilsulfonamidom. Antibacterial properties of the material were studied by determining the growth inhibition zones of test E. coli K12 microorganism in a nutrient medium.Results and Discussion. The structure of synthesized immobilized 4-aminophenylsulfonamide proven by IR spectroscopy. It is shown that such materials exhibit a relatively pronounced antibacterial properties test culture of microorganisms E. coli K-12, in spite of their resistance to hydrolysis. Сonclusions. It is suggested that the hydrolysis of the materials takes place at a specic enzymatic catalysis in the medium with the release of 4-aminophenylsulfonamide.Мета роботи. У сучасних умовах іммобілізація лікарських засобів на полімерних носіях набуває все більшого значення, що пов’язане з вимогами до зменшення токсичності та пролонгації дії препаратів. Відома іммобілізація сульфаніламідних препаратів на стиромалі, метакрилатних полімерних матрицях, де фармакологічно активний сульфаніламід легко вивільняється з полімеру при застосуванні, в результаті кислотного гідролізу. Разом з тим спостерігається, що іммобілізовані сульфаніламіди, отримані на основі амінометильованого співполімеру стиролу з дивінілбензолом, незважаючи на стійкість до гідролізу, зберігають антибактеріальні властивості. З метою розширення прикладів ковалентної іммобілізації сульфаніламідів нами синтезовані 4-амінофенілсульфонаміди на гранульній і волокнистій формах співполімерів стиролу з дивінілбензолом через місткову групу SO2.Матеріали і методи. Як вихідну сировину використано макропористий гранульний співполімер стиролу з дивінілбензолом і сульфовані волокнисті форми прищепленого до поліпропіленової нитки співполімеру стиролу з дивінілбензолом. Сульфохлоруванням цих співполімерів отримано полімерні сульфохлориди, які використовували в реакції з 4-амінофенілсульфонамідом. Антибактеріальні властивості матеріалу досліджені за визначенням зон пригнічення росту тест-мікроорганізмів E.coli К-12 на поживному середовищі.Результати й обговорення. Будову синтезованих іммобілізованих 4-амінофенілсульфонамідів доведено методом ІЧ спектроскопії. Показано, що такі матеріали проявляють виражені антибактеріальні властивості щодо тест-культури мікроорганізмів E. coli К-12, незважаючи на їхню стійкість до гідролізу.Висновки. Зроблено припущення, що гідроліз матеріалів перебігає при специфічному ферментативному каталізі на поживному середовищі виділенням 4-амінофенілсульфонаміду
Cavitation pressure in liquid helium
Recent experiments have suggested that, at low enough temperature, the
homogeneous nucleation of bubbles occurs in liquid helium near the calculated
spinodal limit. This was done in pure superfluid helium 4 and in pure normal
liquid helium 3. However, in such experiments, where the negative pressure is
produced by focusing an acoustic wave in the bulk liquid, the local amplitude
of the instantaneous pressure or density is not directly measurable. In this
article, we present a series of measurements as a function of the static
pressure in the experimental cell. They allowed us to obtain an upper bound for
the cavitation pressure P_cav (at low temperature, P_cav < -2.4 bar in helium
3, P_cav < -8.0 bar in helium 4). From a more precise study of the acoustic
transducer characteristics, we also obtained a lower bound (at low temperature,
P_cav > -3.0 bar in helium 3, P_cav > - 10.4 bar in helium 4). In this article
we thus present quantitative evidence that cavitation occurs at low temperature
near the calculated spinodal limit (-3.1 bar in helium 3 and -9.5 bar in helium
4). Further information is also obtained on the comparison between the two
helium isotopes. We finally discuss the magnitude of nonlinear effects in the
focusing of a sound wave in liquid helium, where the pressure dependence of the
compressibility is large.Comment: 11 pages, 9 figure
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