3,150 research outputs found
Quantum kinetic theory model of a continuous atom laser
We investigate the feasible limits for realising a continuously evaporated
atom laser with high-temperature sources. A plausible scheme for realising a
truly continuous atom laser is to outcouple atoms from a partially condensed
Bose gas, whilst continuously reloading the system with non-condensed thermal
atoms and performing evaporative cooling. Here we use quantum kinetic theory to
model this system and estimate feasible limits for the operation of such a
scheme. For sufficiently high temperatures, the figure of merit for the source
is shown to be the phase-space flux. The dominant process limiting the usage of
sources with low phase-space flux is the three-body loss of the condensed gas.
We conclude that certain double-magneto-optical trap (MOT) sources may produce
substantial mean condensate numbers through continuous evaporation, and provide
an atom laser source with a narrow linewidth and reasonable flux.Comment: 28 pages, 5 figure
Resonance fluorescence in a band gap material: Direct numerical simulation of non-Markovian evolution
A numerical method of calculating the non-Markovian evolution of a driven
atom radiating into a structured continuum is developed. The formal solution
for the atomic reduced density matrix is written as a Markovian algorithm by
introducing a set of additional, virtual density matrices which follow, to the
level of approximation of the algorithm, all the possible trajectories of the
photons in the electromagnetic field. The technique is perturbative in the
sense that more virtual density matrices are required as the product of the
effective memory time and the effective coupling strength become larger. The
number of density matrices required is given by where is the number
of timesteps per memory time. The technique is applied to the problem of a
driven two-level atom radiating close to a photonic band gap and the
steady-state correlation function of the atom is calculated.Comment: 14 pages, 9 figure
High prevalence of scrapie in a dairy goat herd: tissue distribution of disease-associated PrP and effect of PRNP genotype and age
Following a severe outbreak of clinical scrapie in 2006–2007, a
large dairy goat herd was culled
and 200 animals were selected for post-mortem examinations in order to
ascertain the prevalence of infection,
the effect of age, breed and PRNP genotype on the susceptibility to scrapie,
the tissue distribution of diseaseassociated
PrP (PrP), and the comparative efficiency of different diagnostic methods.
As determined by immunohistochemical (IHC) examinations with Bar224 PrP antibody, the
prevalence of preclinical infection
was very high (72/200; 36.0%), with most infected animals being positive
for PrP in lymphoreticular system
(LRS) tissues (68/72; 94.4%) compared to those that were positive in
brain samples (38/72; 52.8%). The
retropharyngeal lymph node and the palatine tonsil showed the highest
frequency of PrP accumulation (87.3%
and 84.5%, respectively), while the recto-anal mucosa-associated lymphoid
tissue (RAMALT) was positive in
only 30 (41.7%) of the infected goats. However, the efficiency of rectal
and palatine tonsil biopsies taken
shortly before necropsy was similar. The probability of brain and RAMALT
being positive directly
correlated with the spread of PrP within the LRS. The prevalence of
infection was influenced by PRNP
genetics at codon 142 and by the age of the goats: methionine carriers older
than 60 months showed a much
lower prevalence of infection (12/78; 15.4%) than those younger than 60 months (20/42; 47.6%); these last
showed prevalence values similar to isoleucine homozygotes of any age
(40/80; 50.0%). Two of seven goats
with definite signs of scrapie were negative for PrP in brain but positive
in LRS tissues, and one goat showed
biochemical and IHC features of PrP different from all other infected
goats. The results of this study have
implications for surveillance and control policies for scrapie in goats
Rotons and Quantum Evaporation from Superfluid 4He
The probability of evaporation induced by and rotons at the
surface of superfluid helium is calculated using time dependent density
functional theory. We consider excitation energies and incident angles such
that phonons do not take part in the scattering process. We predict sizable
evaporation rates, which originate entirely from quantum effects. Results for
the atomic reflectivity and for the probability of the roton change-mode
reflection are also presented.Comment: 11 pages, REVTEX, 3 figures available upon request or at
http://anubis.science.unitn.it/~dalfovo/papers/papers.htm
The steady state quantum statistics of a non-Markovian atom laser
We present a fully quantum mechanical treatment of a single-mode atomic
cavity with a pumping mechanism and an output coupling to a continuum of
external modes. This system is a schematic description of an atom laser. In the
dilute limit where atom-atom interactions are negligible, we have been able to
solve this model without making the Born and Markov approximations. When
coupling into free space, it is shown that for reasonable parameters there is a
bound state which does not disperse, which means that there is no steady state.
This bound state does not exist when gravity is included, and in that case the
system reaches a steady state. We develop equations of motion for the two-time
correlation in the presence of pumping and gravity in the output modes. We then
calculate the steady-state output energy flux from the laser.Comment: 14 pages (twocloumn), 6 figure
Pharmacodynamics of Posaconazole in Experimental Invasive Pulmonary Aspergillosis: Utility of Serum Galactomannan as a Dynamic Endpoint of Antifungal Efficacy
Background. Aspergillus galactomannan antigenemia is an accepted tool for the diagnosis of invasive pulmonary aspergillosis (IPA) in neutropenic patients. Little is known, however, about the utility of this biomarker to assess the efficacy of antifungal therapies. /
Methods. The pharmacokinetics and pharmacodynamics (PK/PD) of posaconazole in treatment and prophylaxis were investigated in the persistently neutropenic rabbit model of Aspergillus fumigatus IPA at doses between 2 and 20 mg/kg and day. Sparse plasma sampling was used to obtain PK data at steady state, and the serum galactomannan index (GMI), as a dynamic endpoint of antifungal response, was obtained every other day in addition to conventional outcome parameters including survival and fungal tissue burden. Nonparametric PK/PD model building was performed using the Pmetrics Package in R. /
Results. A one-compartment model with linear elimination best described the PK of posaconazole. The PD effect of posaconazole exposure in plasma on the GMI in serum was best described by a dynamic Hill-functions reflecting growth and kill of the fungus. Through calculations of the AUC0-24h at steady state, the exposure-response relationship between posaconazole and the GMI for treatment followed a sigmoidal function with an asymptote forming above an AUC0-24h of 30 mg*h/L. All prophylactic doses were able to control the fungal burden. /
Conclusions. A nonparametric population PK/PD model adequately described the effect of posaconazole in prophylaxis and treatment of experimental IPA. An AUC0-24h greater than 30 mg*h/L was associated with adequate resolution of the GMI, which is well in support of previously suggested exposure-response relationships in humans
Effects of interatomic collisions on atom laser outcoupling
We present a computational approach to the outcoupling in a simple
one-dimensional atom laser model, the objective being to circumvent
mathematical difficulties arising from the breakdown of the Born and Markov
approximations. The approach relies on the discretization of the continuum
representing the reservoir of output modes, which allows the treatment of
arbitrary forms of outcoupling as well as the incorporation of non-linear terms
in the Hamiltonian, associated with interatomic collisions. By considering a
single-mode trapped condensate, we study the influence of elastic collisions
between trapped and free atoms on the quasi steady-state population of the
trap, as well as the energy distribution and the coherence of the outcoupled
atoms.Comment: 25 pages, 11 figures, to appear in J. Phys.
Phase dynamics in a binary-collisions atom laser scheme
Various aspects of the phase dynamics of an atom laser scheme based on binary
collisions are investigated. Analytical estimates of the influence of elastic
atom-atom collisions on the laser linewidth are given, and linewidths
achievable in a recently proposed atom laser scheme [Phys. Rev. A 56, 2989
(1997)] are evaluated explicitly. The extent to which a relative phase can be
established between two interfering atom lasers, as well as the properties of
that phase, are also investigated.Comment: Revtex, 10 pages, 6 figure
Ranking Objections to Christian Theism: A Survey of Subjective Declarations and their Correlations with Expert Opinions
There have been numerous books written on the top objections to Christianity—sometimes stated as “common,” “major,” “frequent,” “every day,” “cultural,” “tough,” “difficult” objections. However, there is a dearth of behavioral studies in the literature that show how and given population ranks objections to Christianity. As such, the apologist has had to rely on expert opinions from the books that have been authored. These expert opinions are based on familiarity with the literature in the field and contact with laity from university, church, and other speaking engagements. The purpose of this study is to document trends in how people report the relative strength of objections to Christian theism.[1] We analyze whether these trends correlate with popular works of Christian apologists—our baseline for expert opinion. Further, we determine whether there are any statistically significant relationships between reported demographics, rankings, and attitudes.
Summary of Results and Analysis. Subjective declarations of respondents of the questionnaire showed that most participants were either 18-24 (marginally more than 55-64 and 65-74), male (marginally more than female), had some college (marginally more than bachelor’s, master’s degrees), lived in a suburban community, or lived in the South. In comparing the expert opinion baseline with the aggregate survey ranking results, we see similar rankings between the objection that “God is unloving/immoral” and that the “Bible is not inerrant” (ranked by both as 1st and 2nd, respectively) at the higher end of the spectrum. We found that those identified as agnostic seem to have the closest potential correlation to expert opinion (baseline). The mean of their rankings produced four objections that closely approximated the baseline, one objection that was about one rank removed from the baseline, and three objections that were about two ranks from the baseline. For demographics and rankings, we found statistically significant relationships between religious identification and the objection “God does not exist” with those who identified as atheists, giving it an average ranking of 3.74 (on a scale of 1-13; 1 = highest, 13 = lowest). For demographics and attitudes, we found statistically significant relationships between religious identification and age, religious discussion importance, and attitude toward Christian theism. (See “Analysis” section.)
[1] The study was done under the School of Divinity Department at Liberty University in compliance with Liberty University’s Internal Review Board (Research Ethics Office). IRB-FY21-22-12. Policy: Post-2018 Rule. Submitted 07-06-2021. Last approved 09-07-2021, no expiration date applicable
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