2,016 research outputs found
Magnetism of mixed quaternary Heusler alloys: (Ni,T)MnSn (T=Cu,Pd) as a case study
The electronic properties, exchange interactions, finite-temperature
magnetism, and transport properties of random quaternary Heusler NiMnSn
alloys doped with Cu- and Pd-atoms are studied theoretically by means of {\it
ab initio} calculations over the entire range of dopant concentrations. While
the magnetic moments are only weakly dependent on the alloy composition, the
Curie temperatures exhibit strongly non-linear behavior with respect to
Cu-doping in contrast with an almost linear concentration dependence in the
case of Pd-doping. The present parameter-free theory agrees qualitatively and
also reasonably well quantitatively with the available experimental results. An
analysis of exchange interactions is provided for a deeper understanding of the
problem. The dopant atoms perturb electronic structure close to the Fermi
energy only weakly and the residual resistivity thus obeys a simple Nordheim
rule. The dominating contribution to the temperature-dependent resistivity is
due to thermodynamical fluctuations originating from the spin-disorder, which,
according to our calculations, can be described successfully via the disordered
local moments model. Results based on this model agree fairly well with the
measured values of spin-disorder induced resistivity.Comment: 13 pages, 13 figure
Magnetism of 3d transition metal atoms on W(001): submonolayer films
We have investigated random submonolayer films of 3d transition metals on
W(001). The tight-binding linear muffin-tin orbital method combined with the
coherent potential approximation was employed to calculate the electronic
structure of the films. We have estimated local magnetic moments and the
stability of different magnetic structures, namely the ferromagnetic order, the
disordered local moments and the non-magnetic state, by comparing the total
energies of the corresponding systems. It has been found that the magnetic
moments of V and Cr decrease and eventually disappear with decreasing coverage.
On the other hand, Fe retains approximately the same magnetic moment throughout
the whole concentration range from a single impurity to the monolayer coverage.
Mn is an intermediate case between Cr and Fe since it is non-magnetic at very
low coverages and ferromagnetic otherwise.Comment: 5 pages, 3 figures in 6 files; presented at ICN&T 2006, Basel,
Switzerlan
ΠΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΡ ΠΈΠΎΠ½ΠΈΠ·Π°ΡΠΈΠΈ Π² Π³ΠΎΡΡΡΠ΅ΠΉ ΠΏΠ»ΠΎΡΠΊΠΎΠΉ Π΄ΠΈΡΠΊΠΎΠΎΠ±ΡΠ°Π·Π½ΠΎΠΉ ΠΏΠΎΠ»ΠΎΡΡΠΈ
Hot cavity ion sources of different kinds are widely used in nuclear and mass spectroscopy, especially in on-line isotope separation devices attracting attention of scientists and engineers looking for high ionization efficiency, robustness and beam purity. In the paper a new type of hot ionizer cavity is proposed: namely cavity having the shape of a flat disc, which may be especially suitable for short-lived nuclides to be ionized. A numerical model of the ion source is presented in the paper. The particle tracking code takes into account ionization at hot surfaces and enables modeling of both flat disc cavity and standard elongated cavity ionizers. The code enables calculation of total ionization efficiency and is suitable for stable and long-lived nuclides. Influence of the flat disc cavity geometry (thickness and radius) and its temperature on total ionization efficiency was considered β it was shown that the efficiency increases with cavity radius due to the growing number of particle-wall collisions. This effect may be important in the case of the hard-to-ionize nuclides. The optimal ionizer geometry is characterized by 90 % efficiency, even for substances with rather low ionization coefficient (of order 0.05). The role played by the size of the extraction opening is explained β it is demonstrated that the ionization efficiency increases due to the opening radius reduction. It is also proven that extraction voltage of 1β2 kV is sufficient to maintain optimal ionizer efficiency
Rhythmic Leptin Is Required for Weight Gain from Circadian Desynchronized Feeding in the Mouse
The neuroendocrine and metabolic effects of leptin have been extensively researched since the discovery, and the later identification, of the leptin gene mutated within the ob/ob mouse. Leptin is required for optimal health in a number of physiological systems (e.g. fertility, bone density, body weight regulation). Despite the extensive leptin literature and many observations of leptinβs cyclical pattern over the 24-hour day, few studies have specifically examined how the circadian rhythm of leptin may be essential to leptin signaling and health. Here we present data indicating that a rhythmic leptin profile (e.g. 1 peak every 24 hours) leads to excessive weight gain during desynchronized feeding whereas non-rhythmic leptin provided in a continuous manner does not lead to excessive body weight gain under similar feeding conditions. This study suggests that feeding time can interact with leptinβs endogenous rhythm to influence metabolic signals, specifically leading to excessive body weight gains during βwronglyβ timed feeding
Circadian Disruption and Metabolic Disease: Findings from Animal Models
Social opportunities and work demands have caused humans to become increasingly active during the late evening hours, leading to a shift from the predominantly diurnal lifestyle of our ancestors to a more nocturnal one. This voluntarily decision to stay awake long into the evening hours leads to circadian disruption at the system, tissue, and cellular levels. These derangements are in turn associated with clinical impairments in metabolic processes and physiology. The use of animal models for circadian disruption provides an important opportunity to determine mechanisms by which disorganization in the circadian system can lead to metabolic dysfunction in response to genetic, environmental, and behavioral perturbations. Here we review recent key animal studies involving circadian disruption and discuss the possible translational implications of these studies for human health and particularly for the development of metabolic disease
ΠΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΡ ΠΈΠΎΠ½ΠΈΠ·Π°ΡΠΈΠΈ Π² Π³ΠΎΡΡΡΠ΅ΠΉ ΠΏΠ»ΠΎΡΠΊΠΎΠΉ Π΄ΠΈΡΠΊΠΎΠΎΠ±ΡΠ°Π·Π½ΠΎΠΉ ΠΏΠΎΠ»ΠΎΡΡΠΈ
Hot cavity ion sources of different kinds are widely used in nuclear and mass spectroscopy, especially in on-line isotope separation devices attracting attention of scientists and engineers looking for high ionization efficiency, robustness and beam purity. In the paper a new type of hot ionizer cavity is proposed: namely cavity having the shape of a flat disc, which may be especially suitable for short-lived nuclides to be ionized.A numerical model of the ion source is presented in the paper. The particle tracking code takes into account ionization at hot surfaces and enables modeling of both flat disc cavity and standard elongated cavity ionizers. The code enables calculation of total ionization efficiency and is suitable for stable and long-lived nuclides.Influence of the flat disc cavity geometry (thickness and radius) and its temperature on total ionization efficiency was considered β it was shown that the efficiency increases with cavity radius due to the growing number of particle-wall collisions. This effect may be important in the case of the hard-to-ionize nuclides.The optimal ionizer geometry is characterized by 90 % efficiency, even for substances with rather low ionization coefficient (of order 0.05). The role played by the size of the extraction opening is explained β it is demonstrated that the ionization efficiency increases due to the opening radius reduction. It is also proven that extraction voltage of 1β2 kV is sufficient to maintain optimal ionizer efficiency.Β Β ΠΠΎΠ½ΠΈΠ·Π°ΡΠΎΡΡ Ρ Π³ΠΎΡΡΡΠ΅ΠΉ ΠΏΠΎΠ»ΠΎΡΡΡΡ ΡΠ°Π·Π»ΠΈΡΠ½ΠΎΠ³ΠΎ ΡΠΈΠΏΠ° Π½Π°Ρ
ΠΎΠ΄ΡΡ ΡΠΈΡΠΎΠΊΠΎΠ΅ ΠΏΡΠΈΠΌΠ΅Π½Π΅Π½ΠΈΠ΅ Π² Π°ΡΠΎΠΌΠ½ΠΎΠΉ ΠΈ ΠΌΠ°ΡΡΡΠΏΠ΅ΠΊΡΡΠΎΡΠΊΠΎΠΏΠΈΠΈ, Π² ΡΠ°ΡΡΠ½ΠΎΡΡΠΈ, Π² ΡΡΡΡΠΎΠΉΡΡΠ²Π°Ρ
Π΄Π»Ρ ΡΠ°Π·Π΄Π΅Π»Π΅Π½ΠΈΡ ΠΈΠ·ΠΎΡΠΎΠΏΠΎΠ² Π² ΡΠ΅ΠΆΠΈΠΌΠ΅ ΠΎΠ½Π»Π°ΠΉΠ½, ΠΏΡΠ΅Π΄ΡΡΠ°Π²Π»ΡΡΡ Π±ΠΎΠ»ΡΡΠΎΠΉ ΠΈΠ½ΡΠ΅ΡΠ΅Ρ Π΄Π»Ρ ΡΡΡΠ½ΡΡ
ΠΈ ΠΈΠ½ΠΆΠ΅Π½Π΅ΡΠΎΠ² Π²ΡΠ»Π΅Π΄ΡΡΠ²ΠΈΠ΅ Π²ΡΡΠΎΠΊΠΎΠΉ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΠΈ ΠΈΠΎΠ½ΠΈΠ·Π°ΡΠΈΠΈ, Π½Π°Π΄ΡΠΆΠ½ΠΎΡΡΠΈ ΠΈ ΡΠΈΡΡΠΎΡΡ Π»ΡΡΠ°. Π ΡΠ°Π±ΠΎΡΠ΅ ΠΏΡΠ΅Π΄Π»ΠΎΠΆΠ΅Π½ Π½ΠΎΠ²ΡΠΉ ΡΠΈΠΏ Π³ΠΎΡΡΡΠ΅ΠΉ ΠΈΠΎΠ½ΠΈΠ·Π°ΡΠΈΠΎΠ½Π½ΠΎΠΉ ΠΏΠΎΠ»ΠΎΡΡΠΈ, Π° ΠΈΠΌΠ΅Π½Π½ΠΎ ΠΏΠΎΠ»ΠΎΡΡΠΈ Π² ΡΠΎΡΠΌΠ΅ ΠΏΠ»ΠΎΡΠΊΠΎΠ³ΠΎ Π΄ΠΈΡΠΊΠ°, ΠΎΡΠΎΠ±Π΅Π½Π½ΠΎ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΠΉ Π΄Π»Ρ ΠΈΠΎΠ½ΠΈΠ·Π°ΡΠΈΠΈ ΠΊΠΎΡΠΎΡΠΊΠΎΠΆΠΈΠ²ΡΡΠΈΡ
Π½ΡΠΊΠ»ΠΈΠ΄ΠΎΠ². ΠΡΠ΅Π΄ΡΡΠ°Π²Π»Π΅Π½Π° ΡΠΈΡΠ»Π΅Π½Π½Π°Ρ ΠΌΠΎΠ΄Π΅Π»Ρ ΠΈΠΎΠ½Π½ΠΎΠ³ΠΎ ΠΈΡΡΠΎΡΠ½ΠΈΠΊΠ°. ΠΠΎΠ΄Π΅Π»Ρ ΠΎΡΡΠ»Π΅ΠΆΠΈΠ²Π°Π½ΠΈΡ ΡΠ°ΡΡΠΈΡ ΡΡΠΈΡΡΠ²Π°Π΅Ρ ΠΈΠΎΠ½ΠΈΠ·Π°ΡΠΈΡ Π½Π° Π³ΠΎΡΡΡΠΈΡ
ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΡΡ
ΠΈ ΠΏΠΎΠ·Π²ΠΎΠ»ΡΠ΅Ρ ΠΌΠΎΠ΄Π΅Π»ΠΈΡΠΎΠ²Π°ΡΡ ΠΊΠ°ΠΊ ΠΏΠΎΠ»ΠΎΡΡΡ ΠΏΠ»ΠΎΡΠΊΠΎΠ³ΠΎ Π΄ΠΈΡΠΊΠ°, ΡΠ°ΠΊ ΠΈ ΡΡΠ°Π½Π΄Π°ΡΡΠ½ΡΠ΅ ΠΈΠΎΠ½ΠΈΠ·Π°ΡΠΎΡΡ Ρ ΡΠ΄Π»ΠΈΠ½ΡΠ½Π½ΠΎΠΉ ΠΏΠΎΠ»ΠΎΡΡΡΡ. ΠΠΎΠ΄Π΅Π»Ρ ΠΏΠΎΠ·Π²ΠΎΠ»ΡΠ΅Ρ Π²ΡΠΏΠΎΠ»Π½ΡΡΡ ΡΠ°ΡΡΡΡ ΠΎΠ±ΡΠ΅ΠΉ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΠΈ ΠΈΠΎΠ½ΠΈΠ·Π°ΡΠΈΠΈ ΠΈ ΠΏΡΠΈΠΌΠ΅Π½ΠΈΠΌΠ° ΠΊ ΡΡΠ°Π±ΠΈΠ»ΡΠ½ΡΠΌ ΠΈ Π΄ΠΎΠ»Π³ΠΎΠΆΠΈΠ²ΡΡΠΈΠΌ Π½ΡΠΊΠ»ΠΈΠ΄Π°ΠΌ.Π Π°ΡΡΠΌΠΎΡΡΠ΅Π½ΠΎ Π²Π»ΠΈΡΠ½ΠΈΠ΅ Π³Π΅ΠΎΠΌΠ΅ΡΡΠΈΠΈ ΠΏΠΎΠ»ΠΎΡΡΠΈ ΠΏΠ»ΠΎΡΠΊΠΎΠ³ΠΎ Π΄ΠΈΡΠΊΠ° (ΡΠΎΠ»ΡΠΈΠ½Π° ΠΈ ΡΠ°Π΄ΠΈΡΡ) ΠΈ Π΅Π³ΠΎ ΡΠ΅ΠΌΠΏΠ΅ΡΠ°ΡΡΡΡ Π½Π° ΠΎΠ±ΡΡΡ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΡ ΠΈΠΎΠ½ΠΈΠ·Π°ΡΠΈΠΈ β ΠΏΠΎΠΊΠ°Π·Π°Π½ΠΎ, ΡΡΠΎ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΡ ΡΠ²Π΅Π»ΠΈΡΠΈΠ²Π°Π΅ΡΡΡ Ρ ΡΠ°Π΄ΠΈΡΡΠΎΠΌ ΠΏΠΎΠ»ΠΎΡΡΠΈ ΠΈΠ·-Π·Π° ΡΠ°ΡΡΡΡΠ΅Π³ΠΎ ΡΠΈΡΠ»Π° ΡΡΠΎΠ»ΠΊΠ½ΠΎΠ²Π΅Π½ΠΈΠΉ ΡΠ°ΡΡΠΈΡ ΡΠΎ ΡΡΠ΅Π½ΠΊΠ°ΠΌΠΈ. ΠΠ°Π½Π½ΡΠΉ ΡΡΡΠ΅ΠΊΡ ΠΌΠΎΠΆΠ΅Ρ ΠΎΠΊΠ°Π·Π°ΡΡΡΡ Π²Π°ΠΆΠ΅Π½ Π΄Π»Ρ ΡΡΡΠ΄Π½ΠΎΠΈΠΎΠ½ΠΈΠ·ΠΈΡΡΠ΅ΠΌΡΡ
Π½ΡΠΊΠ»ΠΈΠ΄ΠΎΠ².ΠΠΏΡΠΈΠΌΠ°Π»ΡΠ½Π°Ρ Π³Π΅ΠΎΠΌΠ΅ΡΡΠΈΡ ΠΈΠΎΠ½ΠΈΠ·Π°ΡΠΎΡΠ° Ρ
Π°ΡΠ°ΠΊΡΠ΅ΡΠΈΠ·ΡΠ΅ΡΡΡ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΡΡ 90 % Π΄Π°ΠΆΠ΅ Π΄Π»Ρ ΡΡΡΠ΄Π½ΠΎΠΈΠΎΠ½ΠΈΠ·ΠΈΡΡΠ΅ΠΌΡΡ
Π²Π΅ΡΠ΅ΡΡΠ² Ρ ΠΊΠΎΡΡΡΠΈΡΠΈΠ΅Π½ΡΠΎΠΌ ΠΈΠΎΠ½ΠΈΠ·Π°ΡΠΈΠΈ ΠΏΠΎΡΡΠ΄ΠΊΠ° 0,05. ΠΠ±ΡΡΡΠ½ΡΠ΅ΡΡΡ ΡΠΎΠ»Ρ, ΠΊΠΎΡΠΎΡΡΡ ΠΈΠ³ΡΠ°Π΅Ρ ΡΠ°Π·ΠΌΠ΅Ρ ΡΠΊΡΡΡΠ°ΠΊΡΠΈΠΎΠ½Π½ΠΎΠ³ΠΎ ΠΎΡΠ²Π΅ΡΡΡΠΈΡ β ΠΏΠΎΠΊΠ°Π·Π°Π½ΠΎ, ΡΡΠΎ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΡ ΠΈΠΎΠ½ΠΈΠ·Π°ΡΠΈΠΈ ΡΠ²Π΅Π»ΠΈΡΠΈΠ²Π°Π΅ΡΡΡ ΠΈΠ·-Π·Π° ΡΠΌΠ΅Π½ΡΡΠ΅Π½ΠΈΡ ΡΠ°Π΄ΠΈΡΡΠ° ΠΎΡΠ²Π΅ΡΡΡΠΈΡ. Π’Π°ΠΊΠΆΠ΅ Π΄ΠΎΠΊΠ°Π·Π°Π½ΠΎ, ΡΡΠΎ Π²ΡΡ
ΠΎΠ΄Π½ΠΎΠ΅ Π½Π°ΠΏΡΡΠΆΠ΅Π½ΠΈΠ΅ 1β2 ΠΊΠ Π΄ΠΎΡΡΠ°ΡΠΎΡΠ½ΠΎ Π΄Π»Ρ ΠΏΠΎΠ΄Π΄Π΅ΡΠΆΠ°Π½ΠΈΡ ΠΎΠΏΡΠΈΠΌΠ°Π»ΡΠ½ΠΎΠΉ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΠΈ
Advantages of nonclassical pointer states in postselected weak measurements
We investigate, within the weak measurement theory, the advantages of
non-classical pointer states over semi-classical ones for coherent, squeezed
vacuum, and Schr\"{o}inger cat states. These states are utilized as pointer
state for the system operator with property ,
where represents the identity operator. We calculate the ratio
between the signal-to-noise ratio (SNR) of non-postselected and postselected
weak measurements. The latter is used to find the quantum Fisher information
for the above pointer states. The average shifts for those pointer states with
arbitrary interaction strength are investigated in detail. One key result is
that we find the postselected weak measurement scheme for non-classical pointer
states to be superior to semi-classical ones. This can improve the precision of
measurement process.Comment: 8 pages, 5 figure
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