10,445 research outputs found
Relativistic BCS-BEC crossover in a boson-fermion model
We investigate the crossover from Bardeen-Cooper-Schrieffer (BCS) pairing to
a Bose-Einstein condensate (BEC) in a relativistic superfluid within a
boson-fermion model. The model includes, besides the fermions, separate bosonic
degrees of freedom, accounting for the bosonic nature of the Cooper pairs. The
crossover is realized by tuning the difference between the boson mass and boson
chemical potential as a free parameter. The model yields populations of
condensed and uncondensed bosons as well as gapped and ungapped fermions
throughout the crossover region for arbitrary temperatures. Moreover, we
observe the appearance of antiparticles for sufficiently large values of the
crossover parameter. As an application, we study pairing of fermions with
imbalanced populations. The model can potentially be applied to color
superconductivity in dense quark matter at strong couplings.Comment: ReVTex4, 19 pages, 10 figures; new chapter added about the case of
imbalanced fermion populations; minor modifications to main part; references
adde
Aging is associated with an earlier arrival of reflected waves without a distal shift in reflection sites
Background-Despite pronounced increases in central pulse wave velocity (PWV) with aging, reflected wave transit time (RWTT), traditionally defined as the timing of the inflection point (T-INF) in the central pressure waveform, does not appreciably decrease, leading to the controversial proposition of a "distal-shift" of reflection sites. T-INF, however, is exceptionally prone to measurement error and is also affected by ejection pattern and not only by wave reflection. We assessed whether RWTT, assessed by advanced pressure-flow analysis, demonstrates the expected decline with aging. Methods and Results-We studied a sample of unselected adults without cardiovascular disease (n=48; median age 48 years) and a clinical population of older adults with suspected/established cardiovascular disease (n=164; 61 years). We measured central pressure and flow with carotid tonometry and phase-contrast MRI, respectively. We assessed RWTT using wave-separation analysis (RWTTWSA) and partially distributed tube-load (TL) modeling (RWTTTL). Consistent with previous reports, T-INF did not appreciably decrease with age despite pronounced increases in PWV in both populations. However, aging was associated with pronounced decreases in RWTTWSA (general population -15.0 ms/decade, P<0.001; clinical population -9.07 ms/decade, P=0.003) and RWTTTL (general -15.8 ms/decade, P<0.001; clinical -11.8 ms/decade, P<0.001). There was no evidence of an increased effective reflecting distance by either method. TINF was shown to reliably represent RWTT only under highly unrealistic assumptions about input impedance. Conclusions-RWTT declines with age in parallel with increased PWV, with earlier effects of wave reflections and without a distal shift in reflecting sites. These findings have important implications for our understanding of the role of wave reflections with aging
MOIRCS Deep Survey IV: Evolution of Galaxy Stellar Mass Function Back to z ~ 3
We use very deep near-infrared (NIR) imaging data obtained in MOIRCS Deep
Survey (MODS) to investigate the evolution of the galaxy stellar mass function
back to z~3. The MODS data reach J=24.2, H=23.1, K=23.1 (5sigma, Vega
magnitude) over 103 arcmin^2 (wide) and J=25.1, H=23.7, K=24.1 over 28 arcmin^2
(deep) in the GOODS-North region. The wide and very deep NIR data allow us to
measure the number density of galaxies down to low stellar mass (10^9-10^10
Msun) even at high redshift with high statistical accuracy. The normalization
of the mass function decreases with redshift and the integrated stellar mass
density becomes ~ 8-18% of the local value at z~2 and ~ 4-9% at z~3, which are
consistent with results of previous studies in general fields. Furthermore, we
found that the low-mass slope becomes steeper with redshift from alpha ~- 1.3
at z~1 to alpha ~- 1.6 at z~3, and that the evolution of the number density of
low-mass (10^9-10^10 Msun) galaxies is weaker than that of M* (~10^11 Msun)
galaxies. This indicates that the contribution of low-mass galaxies to the
total stellar mass density has been significant at high redshift. The
steepening of the low-mass slope with redshift is opposite trend expected from
the stellar mass dependence of the specific star formation rate reported in
previous studies. The present result suggests that the hierarchical merging
process overwhelmed the effect of the stellar mass growth by star formation and
was very important for the stellar mass assembly of these galaxies at 1<~z<~3.Comment: 21 pages, 18 figures, accepted for publication in Ap
The Average Physical Properties and Star Formation Histories of the UV-Brightest Star-Forming Galaxies at z~3.7
[Abridged] We investigate the average physical properties and star formation
histories of the most UV-luminous star-forming galaxies at z~3.7. Our results
are derived from analyses of the average spectral energy distributions (SEDs),
constructed from stacked optical to infrared photometry, of a sample of the
1,902 most UV-luminous star-forming galaxies found in 5.3 square degrees of the
NOAO Deep Wide-Field Survey. We bin the sample according to UV luminosity, and
find that the shape of the average SED in the rest-frame optical and infrared
is fairly constant with UV luminosity: i.e., more UV luminous galaxies are, on
average, also more luminous at longer wavelengths. In the rest-UV, however, the
spectral slope (measured at 0.13-0.28 um) rises steeply with the median UV
luminosity from -1.8 at L L* to -1.2 in the brightest bin (L~4-5L*). We use
population synthesis analyses to derive the average physical properties of
these galaxies and find that: (1) L_UV, and thus star formation rates (SFRs),
scale closely with stellar mass such that more UV-luminous galaxies are also
more massive; (2) The median ages indicate that the stellar populations are
relatively young (200-400 Myr) and show little correlation with UV luminosity;
and (3) More UV-luminous galaxies are dustier than their less-luminous
counterparts, such that L~4-5L* galaxies are extincted up to A(1600)=2 mag
while L L* galaxies have A(1600)=0.7-1.5 mag. Based on these observations, we
argue that the average star formation histories of UV-luminous galaxies are
better described by models in which SFR increases with time in order to
simultaneously reproduce the tight correlation between the observed SFR and
stellar mass, and the universally young ages of these galaxies. We demonstrate
the potential of measurements of the SFR-M* relation at multiple redshifts to
discriminate between simple models of star formation histories.Comment: 14 pages, 7 figures. Accepted for publication in Astrophysical
Journa
Vacuumless topological defects in Lyra geometry
Few years ago, Cho and Vilenkin have proposed that topological defects can
arise in symmetry breaking models without having degenerate vacua. These types
of defects are known as vacuumless defects. In the present work, the
gravitational field of a vacuumless global string and global monopole have been
investigated in the context of Lyra geometry. We find the metric of the
vacuumless global string and global monopole in the weak field approximations.
It has been shown that the vacuumless global string can have repulsive whereas
global monopole exerts attractive gravitational effects on a test particle. It
is dissimilar to the case studied in general relativity.Comment: 14 pages, 9 figures. To appear in Astrophys.Space.Sc
Photons in gapless color-flavor-locked quark matter
We calculate the Debye and Meissner masses of a gauge boson in a material
consisting of two species of massless fermions that form a condensate of Cooper
pairs. We perform the calculation as a function of temperature, for the cases
of neutral Cooper pairs and charged Cooper pairs, and for a range of parameters
including gapped quaisparticles, and ungapped quasiparticles with both
quadratic and linear dispersion relations at low energy.
Our results are relevant to the behavior of photons and gluons in the gapless
color-flavor-locked phase of quark matter. We find that the photon's Meissner
mass vanishes, and the Debye mass shows a non-monotonic temperature dependence,
and at temperatures of order the pairing gap it drops to a minimum value of
order sqrt(alpha) times the quark chemical potential. We confirm previous
claims that at zero temperature an imaginary Meissner mass can arise from a
charged gapless condensate, and we find that at finite temperature this can
also occur for a gapped condensate.Comment: 22 pages, LaTeX; expanded discussion of temperature dependenc
Analysis and quantification of the diversities of aerosol life cycles within AeroCom
Simulation results of global aerosol models have been assembled in the framework of the AeroCom intercomparison exercise. In this paper, we analyze the life cycles of dust, sea salt, sulfate, black carbon and particulate organic matter as simulated by sixteen global aerosol models. The diversities among the models for the sources and sinks, burdens, particle sizes, water uptakes, and spatial dispersals have been established. These diversities have large consequences for the calculated radiative forcing and the aerosol concentrations at the surface.
The AeroCom all-models-average emissions are dominated by the mass of sea salt (SS), followed by dust (DU), sulfate (SO_4), particulate organic matter (POM), and finally black carbon (BC). Interactive parameterizations of the emissions and contrasting particles sizes of SS and DU lead generally to higher diversities of these species, and for total aerosol. The lower diversity of the emissions of the fine aerosols, BC, POM, and SO_4, is due to the use of similar emission inventories, and does therefore not necessarily indicate a better understanding of their sources. The diversity of SO_4-sources is mainly caused by the disagreement on depositional loss of precursor gases and on chemical production. The diversities of the emissions are passed on to the burdens, but the latter are also strongly affected by the model-specific treatments of transport and aerosol processes. The burdens of dry masses decrease from largest to smallest: DU, SS, SO_4, POM, and BC.
The all-models-average residence time is shortest for SS with about half a day, followed by S_O4 and DU with four days, and POM and BC with six and seven days, respectively. The wet deposition rate is controlled by the solubility and increases from DU, BC, POM to SO_4 and SS. It is the dominant sink for SO_4, BC, and POM, and contributes about one third to the total removal rate coefficients of SS and DU species. For SS and DU we find high diversities for the removal rate coefficients and deposition pathways. Models do neither agree on the split between wet and dry deposition, nor on that between sedimentation and turbulent dry Deposition. We diagnose an extremely high diversity for the uptake of ambient water vapor that influences the particle size and thus the sink rate coefficients. Furthermore, we find little agreement among the model results for the partitioning of wet removal into scavenging by convective and stratiform rain.
Large differences exist for aerosol dispersal both in the vertical and in the horizontal direction. In some models, a minimum of total aerosol concentration is simulated at the surface. Aerosol dispersal is most pronounced for SO4 and BC and lowest for SS. Diversities are higher for meridional than for vertical dispersal, they are similar for a given species and highest for SS and DU. For these two components we do not find a correlation between vertical and meridional aerosol dispersal. In addition the degree of dispersals of SS and DU is not related to their residence times. SO_4, BC, and POM, however, show increased meridional dispersal in models with larger vertical dispersal, and dispersal is larger for longer simulated residence times
Competition of ferromagnetic and antiferromagnetic spin ordering in nuclear matter
In the framework of a Fermi liquid theory it is considered the possibility of
ferromagnetic and antiferromagnetic phase transitions in symmetric nuclear
matter with Skyrme effective interaction. The zero temperature dependence of
ferromagnetic and antiferromagnetic spin polarization parameters as functions
of density is found for SkM, SGII effective forces. It is shown that in the
density domain, where both type of solutions of self--consistent equations
exist, ferromagnetic spin state is more preferable than antiferromagnetic one.Comment: 9p., 3 figure
Theory of noise suppression in {\Lambda}-type quantum memories by means of a cavity
Quantum memories, capable of storing single photons or other quantum states
of light, to be retrieved on-demand, offer a route to large-scale quantum
information processing with light. A promising class of memories is based on
far-off-resonant Raman absorption in ensembles of -type atoms. However
at room temperature these systems exhibit unwanted four-wave mixing, which is
prohibitive for applications at the single-photon level. Here we show how this
noise can be suppressed by placing the storage medium inside a moderate-finesse
optical cavity, thereby removing the main roadblock hindering this approach to
quantum memory.Comment: 10 pages, 3 figures. This paper provides the theoretical background
to our recent experimental demonstration of noise suppression in a
cavity-enhanced Raman-type memory ( arXiv:1510.04625 ). See also the related
paper arXiv:1511.05448, which describes numerical modelling of an atom-filled
cavity. Comments welcom
Contact force sensing in ablation of ventricular arrhythmias using a 56-hole open-irrigation catheter: a propensity-matched analysis.
PURPOSE: The effect of adding contact force (CF) sensing to 56-hole tip irrigation in ventricular arrhythmia (VA) ablation has not been previously studied. We aimed to compare outcomes with and without CF sensing in VA ablation using a 56-hole radiofrequency (RF) catheter. METHODS: A total of 164 patients who underwent first-time VA ablation using Thermocool SmartTouch Surround Flow (TC-STSF) catheter (Biosense-Webster, Diamond Bar, CA, USA) were propensity-matched in a 1:1 fashion to 164 patients who had first-time ablation using Thermocool Surround Flow (TC-SF) catheter. Patients were matched for age, gender, cardiac aetiology, ejection fraction and approach. Acute success, complications and long-term follow-up were compared. RESULTS: There was no difference between procedures utilising either TC-SF or TC-STSF in acute success (TC-SF: 134/164 (82%), TC-STSF: 141/164 (86%), p = 0.3), complications (TC-SF: 11/164 (6.7%), TC-STSF: 11/164 (6.7%), p = 1.0) or VA-free survival (TC-SF: mean arrhythmia-free survival time = 5.9 years, 95% CI = 5.4-6.4, TC-STSF: mean = 3.2 years, 95% CI = 3-3.5, log-rank p = 0.74). Fluoroscopy time was longer in normal hearts with TC-SF (19 min, IQR: 14-30) than TC-STSF (14 min, IQR: 8-25; p = 0.04). CONCLUSION: Both TC-SF and TC-STSF catheters are safe and effective in treating VAs. The use of CF sensing catheters did not improve safety or acute and long-term outcomes, but reduced fluoroscopy time in normal heart VA
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