10,423 research outputs found
Sharp increase of the effective mass near the critical density in a metallic 2D electron system
We find that at intermediate temperatures, the metallic temperature
dependence of the conductivity \sigma(T) of 2D electrons in silicon is
described well by a recent interaction-based theory of Zala et al. (Phys. Rev.
B 64, 214204 (2001)). The tendency of the slope d\sigma/dT to diverge near the
critical electron density is in agreement with the previously suggested
ferromagnetic instability in this electron system. Unexpectedly, it is found to
originate from the sharp enhancement of the effective mass, while the effective
Lande g factor remains nearly constant and close to its value in bulk silicon
Flow diagram of the metal-insulator transition in two dimensions
The discovery of the metal-insulator transition (MIT) in two-dimensional (2D)
electron systems challenged the veracity of one of the most influential
conjectures in the physics of disordered electrons, which states that `in two
dimensions, there is no true metallic behaviour'; no matter how weak the
disorder, electrons would be trapped and unable to conduct a current. However,
that theory did not account for interactions between the electrons. Here we
investigate the interplay between the electron-electron interactions and
disorder near the MIT using simultaneous measurements of electrical resistivity
and magnetoconductance. We show that both the resistance and interaction
amplitude exhibit a fan-like spread as the MIT is crossed. From these data we
construct a resistance-interaction flow diagram of the MIT that clearly reveals
a quantum critical point, as predicted by the two-parameter scaling theory
(Punnoose and Finkel'stein, Science 310, 289 (2005)). The metallic side of this
diagram is accurately described by the renormalization group theory without any
fitting parameters. In particular, the metallic temperature dependence of the
resistance sets in when the interaction amplitude reaches gamma_2 = 0.45 - a
value in remarkable agreement with the one predicted by the theory.Comment: as publishe
Metal-insulator transition in a 2D electron gas: Equivalence of two approaches for determining the critical point
The critical electron density for the metal-insulator transition in a
two-dimensional electron gas can be determined by two distinct methods: (i) a
sign change of the temperature derivative of the resistance, and (ii) vanishing
activation energy and vanishing nonlinearity of current-voltage characteristics
as extrapolated from the insulating side. We find that in zero magnetic field
(but not in the presence of a parallel magnetic field), both methods give
equivalent results, adding support to the existence of a true zero-field
metal-insulator transition.Comment: As publishe
A Droplet State in an Interacting Two-Dimensional Electron System
It is well known that the dielectric constant of two-dimensional (2D)
electron system goes negative at low electron densities. A consequence of the
negative dielectric constant could be the formation of the droplet state. The
droplet state is a two-phase coexistence region of high density liquid and low
density "gas". In this paper, we carry out energetic calculations to study the
stability of the droplet ground state. The possible relevance of the droplet
state to recently observed 2D metal-insulator transition is also discussed.Comment: 4 pages, 4 figures. To appear in Phys. Rev. B (Rapid Communications
Ground state properties of the 2D disordered Hubbard model
We study the ground state of the two-dimensional (2D) disordered Hubbard
model by means of the projector quantum Monte Carlo (PQMC) method. This
approach allows us to investigate the ground state properties of this model for
lattice sizes up to , at quarter filling, for a broad range of
interaction and disorder strengths. Our results show that the ground state of
this system of spin-1/2 fermions remains localised in the presence of the
short-ranged Hubbard interaction.Comment: 7 pages, 9 figure
Development of a food antioxidant complex of plant origin
Розроблено антиоксидантний комплекс для використання в оліях, жирах та продуктах харчування, що потребують збагачення біологічно активними речовинами рослинного походження. Досліджено раціональні умови одержан- ня водно-етанольних екстрактів із рослинної сировини: кори дубу, листя евкаліпту та листя зеленого чаю. Отримано антиоксидант, що здатен запобігати окисненню жировмісних продуктів, зберігаючи їх високу поживну цінність. Антиоксидантні речовини природного походження дозволять створювати збалансовані за складом продукти з підвищеним строком придатності із збереженням початкового природного складу та структури компонентів. Також розроблений антиоксидант є додатковим джерелом речовин, що допомагають організму боротися з вільними радикалами, що утворюються внаслідок фізичних та психічних навантажень. До складу антиоксидантів рослинного походжен- ня входять антиоксидантні вітаміни (токофероли та аскорбінова кислота), рослинні феноли та тиолові антиоксиданти (глутатіон, ліпоєва кислота), мікроелементи. Ці складові беруть участь у процесах гальмування окиснення. Також до таких антиоксидантів входять селен, цинк,
фолати та інші речовини. Для планування експериментальних досліджень для кожного виду рослинної сировини стосовно антиоксидантної активності виділених речовин використано повний факторний експеримент першого порядку. Виявлено синергізм дії антиоксидантних речовин при одночасному використанні екстрактів з кори дубу, листя евкаліпта, листя зеленого чаю. Розроблений антиоксидант підвищує період індукції модельної речовини (олії соняшникової) у 2,7 рази, тоді як під час використання антиоксидантів окремо з кожного виду рослин найкращий показник збільшення періоду індукції склав 1,9.
Отже, розроблений антиоксидант здатен сприяти збереженню якості і безпечності жировмісних продуктів харчування. Використання даного антиоксиданту може бути запропоновано для продуктів харчування людей, що потребують додаткового введення антиоксидантів та біологічно активних речовин до раціону харчування. Зокрема, це важливо для спортсменів
Sex and Age Differences in Lipoprotein Metabolism Proatherogenic Changes under the Experimental Metabolic Syndrome in Hamsters
The unbalanced high-calorie diet can be the cause of a number of pathological states, including metabolic syndrome (MS). It is well known that the risk of MS increases with age, but gender differences in age-related lipid metabolism changes under this pathology are not fully understood
IceCube-Plus: An Ultra-High Energy Neutrino Telescope
While the first kilometer-scale neutrino telescope, IceCube, is under
construction, alternative plans exist to build even larger detectors that will,
however, b e limited by a much higher neutrino energy threshold of 10 PeV or
higher rather than 10 to 100 GeV. These future projects detect radio and
acoustic pulses as w ell as air showers initiated by ultra-high energy
neutrinos. As an alternative, we here propose an expansion of IceCube, using
the same strings, placed on a gri d with a spacing of order 500 m. Unlike other
proposals, the expanded detector uses methods that are understood and
calibrated on atmospheric neutrinos. Atmosp heric neutrinos represent the only
background at the energies under consideratio n and is totally negligible.
Also, the cost of such a detector is understood. We conclude that supplementing
the 81 IceCube strings with a modest number of addi tional strings spaced at
large distances can almost double the effective volume of the detector.
Doubling the number of strings on a 800 m grid can deliver a d etector that
this a factor of 5 larger for horizontal muons at modest cost.Comment: Version to be published in JCA
On Lebesgue measure of integral self-affine sets
Let be an expanding integer matrix and be a finite subset
of . The self-affine set is the unique compact set satisfying
the equality . We present an effective algorithm to
compute the Lebesgue measure of the self-affine set , the measure of
intersection for , and the measure of intersection of
self-affine sets for different sets .Comment: 5 pages, 1 figur
Indication of the ferromagnetic instability in a dilute two-dimensional electron system
The magnetic field B_c, in which the electrons become fully spin-polarized,
is found to be proportional to the deviation of the electron density from the
zero-field metal-insulator transition in a two-dimensional electron system in
silicon. The tendency of B_c to vanish at a finite electron density suggests a
ferromagnetic instability in this strongly correlated electron system.Comment: 4 pages, postscript figures included. Revised versio
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