734 research outputs found
Effect of thermal fluctuations on spin degrees of freedom in spinor Bose-Einstein condensates
We consider the effect of thermal fluctuations on rotating spinor F=1
condensates in axially-symmetric vortex phases, when all the three hyperfine
states are populated. We show that the relative phase among different
components of the order parameter can fluctuate strongly due to the weakness of
the interaction in the spin channel. These fluctuations can be significant even
at low temperatures. Fluctuations of relative phase lead to significant
fluctuations of the local transverse magnetization of the condensate. We
demonstrate that these fluctuations are much more pronounced for the
antiferromagnetic state than for the ferromagnetic one.Comment: 5 pages, 2 figures; final version, accepted for publication in Phys.
Rev.
Dynamic analysis of groundwater discharge and partial-area contribution to Pukemanga Stream, New Zealand
The proportion and origin of groundwater contribution to streamflow from agricultural catchments is relevant to estimation of the effects of nitrate leached from the soil on the quality of surface waters. This study addresses the partitioning of streamflow contributions from near-surface runoff and from groundwater, each with different contributing land area, on a steep pastoral hillslope in a humid climate. The 3 ha headwater catchment of the perennial Pukemanga Stream, in the North Island of New Zealand, was instrumented for continuous observation of climatic data, streamflow and groundwater level. The dynamics of groundwater levels and groundwater contribution to streamflow were analysed by means of a one-parameter, eigenvalue-eigenfunction description of a 1-D aquifer model. Model results for seven years of daily data predict that 36–44% of the topographical catchment contributes groundwater to the stream. The remaining groundwater generated within the catchment contributes to streamflow outside the catchment. Groundwater was calculated to be 58–83% of observed annual streamflow from the topographical catchment. When the smaller groundwater catchment is taken into account, the groundwater contribution to streamflow is 78–93% on a unit area basis. Concurrent hourly data for streamflow and groundwater levels at two sites indicate the dynamic behaviour of a local groundwater system. Groundwater flow dynamics that support the perennial nature of this headwater stream are consistent with the size of the groundwater body, porosity of the subsurface material, and hydraulic conductivity derived from partitioning of streamflow contributions
Vortex structure in spinor F=2 Bose-Einstein condensates
Extended Gross-Pitaevskii equations for the rotating F=2 condensate in a
harmonic trap are solved both numerically and variationally using trial
functions for each component of the wave function. Axially-symmetric vortex
solutions are analyzed and energies of polar and cyclic states are calculated.
The equilibrium transitions between different phases with changing of the
magnetization are studied. We show that at high magnetization the ground state
of the system is determined by interaction in "density" channel, and at low
magnetization spin interactions play a dominant role. Although there are five
hyperfine states, all the particles are always condensed in one, two or three
states. Two novel types of vortex structures are also discussed.Comment: 6 pages, 3 figure
Ultra-precise measurement of optical frequency ratios
We developed a novel technique for frequency measurement and synthesis, based
on the operation of a femtosecond comb generator as transfer oscillator. The
technique can be used to measure frequency ratios of any optical signals
throughout the visible and near-infrared part of the spectrum. Relative
uncertainties of for averaging times of 100 s are possible. Using a
Nd:YAG laser in combination with a nonlinear crystal we measured the frequency
ratio of the second harmonic at 532 nm to the fundamental at
1064 nm, .Comment: 4 pages, 4 figure
A New Option for a Search for Alpha Variation: Narrow Transitions with Enhanced Sensitivity
We consider several transitions between narrow lines that have an enhanced
sensitivity to a possible variation of the fine structure constant, alpha. This
enhancement may allow a search to be performed with an effective suppression of
the systematic sources of uncertainty that are unavoidable in conventional
high-resolution spectroscopic measurements. In the future this may provide the
strongest laboratory constraints on alpha variation
Korringa ratio of ferromagnetically correlated impure metals
The Korringa ratio, , obtained by taking an appropriate combination
of the Knight shift and nuclear spin-lattice relaxation time, is calculated at
finite temperature, , in the three-dimensional electron gas model, including
the electron-electron interaction, , and non-magnetic impurity scatterings.
varies in a simple way with respect to and ; it decreases as
is increased but increases as is raised. However, varies in a
slightly more complicated way with respect to the impurity scatterings; as the
scattering rate is increased, increases for small and low , but
decreases for large or high regime. This calls for a more careful
analysis when one attempts to estimate the Stoner factor from .Comment: 7 pages including 3 figures. To be published in Phys. Rev. B, Dec.
Search for gamma-rays from M31 and other extragalactic objects
Although the existence of fluxes of gamma-rays of energies 10 to the 12th power eV is now established for galactic sources, the detection of such gamma-rays from extragalactic sources has yet to be independently confirmed in any case. The detection and confirmation of such energetic photons is of great astrophysical importance in the study of production mechanisms for cosmic rays, and other high energy processes in extragalactic objects. Observations of m31 are discussed. It is reported as a 10 to the 12th power eV gamma-ray source. Flux limits on a number of other extragalactic objects chosen for study are given
Variability in the high energy gamma ray emission from Cyg X-3 over a two-year period (1983 - 1984) at E 4 x 10(11) eV
Cygnus X-3 is observed to emit gamma rays with energies in excess of 4 x 10 to the 11th power eV during two out of 9 observational categories over an 18 month time span. The emissions are observed at the 0.6 phase of the characteristic 4.8 hr light curve for this binary system. We estimate a peak flux at phase 0.6 of 5 x 10 to the minus 10th power photons cm-2s-1 at a software threshold of 8 x 10 to the 11th power eV for Oct/Nov 1983. A flux for the June 84 effect cannot be reliably calculated at present due to lack of Monte Carlo simulations for the energy range and spectral region. For the other 7 observational categories the observations are consistent with zero source emission. The light curve would appear to be variable on a time scale of a couple of weeks at these categories. Selection of compact images in accordance with Monte Carlo simulations combined with empirical optimization techniques have led to an enriched gamma ray light curve for the Oct/Nov 1983 data. Selection on the basis of shower orientation, however, has not led to any notable enhancement of the gamma ray content. Individual Cherenko images can be reliably sorted on an event by event basis into either proton-induced or photon-induced showers
ORIGINAL ARTICLES Can’t Shake that Feeling: Event-Related fMRI Assessment of Sustained Amygdala Activity in Response to Emotional Information in Depressed Individuals
individuals engage in prolonged elaborative processing of emotional information. A computational neural network model of emotional information processing suggests this process involves sustained amygdala activity in response to processing negative features of information. This study examined whether brain activity in response to emotional stimuli was sustained in depressed individuals, even following subsequent distracting stimuli. Methods: Seven depressed and 10 never-depressed individuals were studied using event-related functional magnetic resonance imaging during alternating 15-sec emotional processing (valence identification) and nonemotional processing (Sternberg memory) trials. Amygdala regions were traced on high-resolution structural scans and coregistered to the functional data. The time course of activity in these areas during emotional and nonemotional processing trials was examined. Results: During emotional processing trials, never-depressed individuals displayed amygdalar responses to all stimuli, which decayed within 10 sec. In contrast, depressed individuals displayed sustained amygdala responses to negative words that lasted throughout the following nonemotional processing trials (25 sec later). The difference in sustained amygdala activity to negative and positive words was moderately related to self-reported rumination. Conclusions: Results suggest that depression is associated with sustained activity in brain areas responsible for coding emotional features. Biol Psychiatry 2002;51
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