20,187 research outputs found
Partial spin freezing in the quasi-two-dimensional La2(Cu,Li)O4
In conventional spin glasses, the magnetic interaction is not strongly
anisotropic and the entire spin system freezes at low temperature. In
La2(Cu,Li)O4, for which the in-plane exchange interaction dominates the
interplane one, only a fraction of spins with antiferromagnetic correlations
extending to neighboring planes become spin-glass. The remaining spins with
only in-plane antiferromagnetic correlations remain spin-liquid at low
temperature. Such a novel partial spin freezing out of a spin-liquid observed
in this cold neutron scattering study is likely due to a delicate balance
between disorder and quantum fluctuations in the quasi-two dimensional S=1/2
Heisenberg system.Comment: 4 pages, 4 figure
Two--Electron Atoms in Short Intense Laser Pulses
We discuss a method of solving the time dependent Schrodinger equation for
atoms with two active electrons in a strong laser field, which we used in a
previous paper [A. Scrinzi and B. Piraux, Phys. Rev. A 56, R13 (1997)] to
calculate ionization, double excitation and harmonic generation in Helium by
short laser pulses. The method employs complex scaling and an expansion in an
explicitly correlated basis. Convergence of the calculations is documented and
error estimates are provided. The results for Helium at peak intensities up to
10^15 W/cm^2 and wave length 248 nm are accurate to at least 10 %. Similarly
accurate calculations are presented for electron detachment and double
excitation of the negative hydrogen ion.Comment: 14 pages, including figure
Quasiparticles in the 111 state and its compressible ancestors
We investigate the relationship of the spontaneously inter-layer coherent
``111''state of quantum Hall bilayers at total filling factor \nu=1 to
``mutual'' composite fermions, in which vortices in one layer are bound to
electrons in the other. Pairing of the mutual composite fermions leads to the
low-energy properties of the 111 state, as we explicitly demonstrate using
field-theoretic techniques. Interpreting this relationship as a mechanism for
inter-layer coherence leads naturally to two candidate states with
non-quantized Hall conductance: the mutual composite Fermi liquid, and an
inter-layer coherent charge e Wigner crystal. The experimental behavior of the
interlayer tunneling conductance and resistivity tensors are discussed for
these states.Comment: 4 Pages, RevTe
Dual neutral variables and knot solitons in triplet superconductors
In this paper we derive a dual presentation of free energy functional for
spin-triplet superconductors in terms of gauge-invariant variables. The
resulting equivalent model in ferromagnetic phase has a form of a version of
the Faddeev model. This allows one in particular to conclude that spin-triplet
superconductors allow formation of stable finite-length closed vortices (the
knotted solitons).Comment: Replaced with version published in PRL (added a discussion of the
effect of the coupling of the fields {\vec s} and {\vec C} on knot
stability). Latest updates of the paper and miscellaneous links related to
knotted solitons are also available at the homepage of the author
http://www.teorfys.uu.se/PEOPLE/egor/ . Animations of knotted solitons by
Hietarinta and Salo are available at
http://users.utu.fi/h/hietarin/knots/c45_p2.mp
Betel quid chewing as a risk factor for hepatocellular carcinoma: a case-control study
The role of betel quid chewing in the aetiology of hepatocellular carcinoma (HCC) was evaluated in a case–control study including 263 pairs of age- and sex-matched HCC patients and healthy controls. Serum hepatitis B surface antigen (HBsAg), and antibodies to hepatitis C virus (anti-HCV) were determined, and standardized personal interview conducted using a structured questionnaire. Multivariate analysis indicated that betel quid chewing (odds ratio (OR), 3.49; 95% confidence interval (CI), 1.74–6.96), HBsAg (OR, 16.69; 95% CI, 9.92–28.07), anti-HCV (OR, 38.57; 95% CI, 18.15–81.96), and educational duration of less than 10 years (OR, 1.71; 95% CI, 1.05–2.78) are independent risk factors of HCC. In addition, there was an additive interaction between betel quid chewing and chronic infection with either hepatitis B virus (synergy index, 5.37) or hepatitis C virus (synergy index, 1.66). Moreover, risk on HCC increased as duration of betel quid chewing increased, or amount of betel quid consumed (each P for trend < 0.0001). © 2001 Cancer Research Campaign http://www.bjcancer.co
KK6 from M2 in BLG
We study the possibility that the Kaluza-Klein monopole (KK6) world-volume
action may be obtained from the multiple membranes (M2) action which is
described by BLG theory. We first point out that the infinite dimensional Lie
3-algebra based on the Nambu-Poisson structure could not only provide three
dimensional manifolds to allow M5 from M2, which was studied by previous
authors, but also provide five dimensional manifolds to allow KK6 from M2. We
next present a possible way that the U(1) field on KK6 world-volume action
could be produced form the gauge potential in BLG theory.Comment: Latex, 15 pages. V3: Add theorem 2 to complete proof. V4: Detail
physical interpretations and calculations in section
Respondents of health survey powered by the innovative NURO app exhibit correlations between exercise frequencies and diet habits, and between stress levels and sleep wellness
Nurosene's NURO app (nurosene.com) is an innovative smartphone application that gathers and analyzes active self-report metrics from users, empowering them with data-driven health machine intelligence. We present the data collected and analyzed from the initial round of participants who responded to a 12-question survey on their life-style and health status. Exploratory results using a variational autoencoder (VAE) suggested that much of the variability of the 12 dimensional data could be accounted for by two approximately uncorrelated latent variables: one pertaining to stress and sleep, and the other pertaining to exercise and diet. Subsequent modeling of the data using exploratory and confirmatory factor analyses (EFAs and CFAs) found that optimal data fits consisted of four factors, namely exercise, diet, stress, and sleep. Covariance values were high between exercise and diet, and between stress and sleep, but much lower between other pairings of non-identical factors. Both EFAs and CFAs provided extra contexts to and quantified the more preliminary VAE observations. Overall, our results significantly reduce the apparent complexity of the response data. This reduction allows for more efficient future stratification and analyses of participants based on simpler latent variables. Our discovery of novel relationships between stress and sleep, and between exercise and diet suggests the possibility of applying predictive analytics in future efforts
Exploring the Thermodynamics of a Universal Fermi Gas
From sand piles to electrons in metals, one of the greatest challenges in
modern physics is to understand the behavior of an ensemble of strongly
interacting particles. A class of quantum many-body systems such as neutron
matter and cold Fermi gases share the same universal thermodynamic properties
when interactions reach the maximum effective value allowed by quantum
mechanics, the so-called unitary limit [1,2]. It is then possible to simulate
some astrophysical phenomena inside the highly controlled environment of an
atomic physics laboratory. Previous work on the thermodynamics of a
two-component Fermi gas led to thermodynamic quantities averaged over the trap
[3-5], making it difficult to compare with many-body theories developed for
uniform gases. Here we develop a general method that provides for the first
time the equation of state of a uniform gas, as well as a detailed comparison
with existing theories [6,14]. The precision of our equation of state leads to
new physical insights on the unitary gas. For the unpolarized gas, we prove
that the low-temperature thermodynamics of the strongly interacting normal
phase is well described by Fermi liquid theory and we localize the superfluid
transition. For a spin-polarized system, our equation of state at zero
temperature has a 2% accuracy and it extends the work of [15] on the phase
diagram to a new regime of precision. We show in particular that, despite
strong correlations, the normal phase behaves as a mixture of two ideal gases:
a Fermi gas of bare majority atoms and a non-interacting gas of dressed
quasi-particles, the fermionic polarons [10,16-18].Comment: 8 pages, 5 figure
Multi-indexed (q-)Racah Polynomials
As the second stage of the project multi-indexed orthogonal polynomials, we
present, in the framework of `discrete quantum mechanics' with real shifts in
one dimension, the multi-indexed (q-)Racah polynomials. They are obtained from
the (q-)Racah polynomials by multiple application of the discrete analogue of
the Darboux transformations or the Crum-Krein-Adler deletion of `virtual state'
vectors, in a similar way to the multi-indexed Laguerre and Jacobi polynomials
reported earlier. The virtual state vectors are the `solutions' of the matrix
Schr\"odinger equation with negative `eigenvalues', except for one of the two
boundary points.Comment: 29 pages. The type II (q-)Racah polynomials are deleted because they
can be obtained from the type I polynomials. To appear in J.Phys.
A ROSAT HRI survey of bright nearby galaxies
We use the extensive public archive of ROSAT High Resolution Imager (HRI)
observations to carry out a statistical investigation of the X-ray properties
of nearby galaxies. Specifically we focus on the sample of 486 bright (B_T <
12.5) northern galaxies studied by Ho, Filippenko and Sargent (HFS) in the
context of their exploration of the optical spectroscopic properties of nearby
galactic nuclei. Over 20% of HFS galaxies are encompassed in ROSAT HRI fields
of reasonable (> 10ks) exposure. The X-ray sources detected within the optical
extent of each galaxy are categorised as either nuclear or non-nuclear
depending on whether the source is positioned within or outside of a 25
arcsecond radius circle centred on the optical nucleus. A nuclear X-ray source
is detected in over 70% of the galaxies harbouring either a Seyfert or LINER
nucleus compared to a detection rate of only ~40% in less active systems. The
correlation of the H alpha luminosity with nuclear X-ray luminosity previously
observed in QSOs and bright Seyfert 1 galaxies appears to extend down into the
regime of ultra-low luminosity (L(x)~10^38 - 10^40 erg/s) active galactic
nuclei (AGN). The inferred accretion rates for this sample of low-luminosity
AGN are significantly sub-Eddington. In total 142 non-nuclear sources were
detected. In combination with published data for M31 this leads to a luminosity
distribution (normalised to an optical blue luminosity of L(B) = 10^10
L(solar)) for the discrete X-ray source population in spiral galaxies of the
form dN/dL38 = 1.0 +/- 0.2 L38^-1.8, where L38 is the X-ray luminosity in units
of 10^38 erg/s. The implied L(x)/L(B) ratio is ~1.1 x 10^39 erg/s/(10^10
L(solar)). The nature of the substantial number of ``super-luminous''
non-nuclear objects detected in the survey is discussed.Comment: 20 pages, 7 figures, accepted for publication in MNRAS. Also
available from http://www.star.le.ac.uk/~tro/papers/xhfs.p
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