918 research outputs found
Quantum catastrophe of slow light
Catastrophes are at the heart of many fascinating optical phenomena. The
rainbow, for example, is a ray catastrophe where light rays become infinitely
intense. The wave nature of light resolves the infinities of ray catastrophes
while drawing delicate interference patterns such as the supernumerary arcs of
the rainbow. Black holes cause wave singularities. Waves oscillate with
infinitely small wave lengths at the event horizon where time stands still. The
quantum nature of light avoids this higher level of catastrophic behaviour
while producing a quantum phenomenon known as Hawking radiation. As this letter
describes, light brought to a standstill in laboratory experiments can suffer a
similar wave singularity caused by a parabolic profile of the group velocity.
In turn, the quantum vacuum is forced to create photon pairs with a
characteristic spectrum. The idea may initiate a theory of quantum
catastrophes, in addition to classical catastrophe theory, and the proposed
experiment may lead to the first direct observation of a phenomenon related to
Hawking radiation.Comment: Published as "A laboratory analogue of the event horizon using slow
light in an atomic medium
Mechanisms of gap gene expression canalization in the Drosophila blastoderm
<p>Abstract</p> <p>Background</p> <p>Extensive variation in early gap gene expression in the <it>Drosophila </it>blastoderm is reduced over time because of gap gene cross regulation. This phenomenon is a manifestation of canalization, the ability of an organism to produce a consistent phenotype despite variations in genotype or environment. The canalization of gap gene expression can be understood as arising from the actions of attractors in the gap gene dynamical system.</p> <p>Results</p> <p>In order to better understand the processes of developmental robustness and canalization in the early <it>Drosophila </it>embryo, we investigated the dynamical effects of varying spatial profiles of Bicoid protein concentration on the formation of the expression border of the gap gene <it>hunchback</it>. At several positions on the anterior-posterior axis of the embryo, we analyzed attractors and their basins of attraction in a dynamical model describing expression of four gap genes with the Bicoid concentration profile accounted as a given input in the model equations. This model was tested against a family of Bicoid gradients obtained from individual embryos. These gradients were normalized by two independent methods, which are based on distinct biological hypotheses and provide different magnitudes for Bicoid spatial variability. We showed how the border formation is dictated by the biological initial conditions (the concentration gradient of maternal Hunchback protein) being attracted to specific attracting sets in a local vicinity of the border. Different types of these attracting sets (point attractors or one dimensional attracting manifolds) define several possible mechanisms of border formation. The <it>hunchback </it>border formation is associated with intersection of the spatial gradient of the maternal Hunchback protein and a boundary between the attraction basins of two different point attractors. We demonstrated how the positional variability for <it>hunchback </it>is related to the corresponding variability of the basin boundaries. The observed reduction in variability of the <it>hunchback </it>gene expression can be accounted for by specific geometrical properties of the basin boundaries.</p> <p>Conclusion</p> <p>We clarified the mechanisms of gap gene expression canalization in early <it>Drosophila </it>embryos. These mechanisms were specified in the case of <it>hunchback </it>in well defined terms of the dynamical system theory.</p
Description and evaluation of an EBM curriculum using a block rotation
BACKGROUND: While previous authors have emphasized the importance of integrating and reinforcing evidence-based medicine (EBM) skills in residency, there are few published examples of such curricula. We designed an EBM curriculum to train family practice interns in essential EBM skills for information mastery using clinical questions generated by the family practice inpatient service. We sought to evaluate the impact of this curriculum on interns, residents, and faculty. METHODS: Interns (n = 13) were asked to self-assess their level of confidence in basic EBM skills before and after their 2-week EBM rotation. Residents (n = 21) and faculty (n = 12) were asked to assess how often the answers provided by the EBM intern to the inpatient service changed medical care. In addition, residents were asked to report how often they used their EBM skills and how often EBM concepts and tools were used in teaching by senior residents and faculty. Faculty were asked if the EBM curriculum had increased their use of EBM in practice and in teaching. RESULTS: Interns significantly increased their confidence over the course of the rotation. Residents and faculty felt that the answers provided by the EBM intern provided useful information and led to changes in patient care. Faculty reported incorporating EBM into their teaching (92%) and practice (75%). Residents reported applying the EBM skills they learned to patient care (86%) and that these skills were reinforced in the teaching they received outside of the rotation (81%). All residents and 11 of 12 faculty felt that the EBM curriculum had improved patient care. CONCLUSIONS: To our knowledge, this is the first published EBM curriculum using an individual block rotation format. As such, it may provide an alternative model for teaching and incorporating EBM into a residency program
Prevalence, evaluation and management of overactive bladder in primary care
<p>Abstract</p> <p>Background</p> <p>Patients with overactive bladder (OAB) are under-diagnosed in the primary care setting. Primary care physicians (PCP) approach to the patient and appropriate patient disclosure may contribute to under-diagnosis.</p> <p>Methods</p> <p>An outpatient primary care setting was used to determine the prevalence and characteristics of OAB. Patients who visited the family medicine outpatient clinic were invited to answer a self-administered questionnaire. It included questions on evidence of lower urinary tract symptoms (modified Overactive Bladder-Validated 8-question Screener [OAB-V8]), relevant medical and surgical history, and demographic data. Relationship between OAB and other independent variables were analyzed using chi-square and risk ratio (RR) analysis.</p> <p>Results</p> <p>Of 325 questionnaires distributed, 311 were returned completed. Patients ranged from 18 to 97 years, the majority women (74.0%) and African American (74.3%). OAB was present in 60.5% of men and 48.3% of women (<it>p </it>= 0.058). OAB was significantly associated with obesity (BMI > = 30) in women (<it>p </it>= 0.018, RR = 1.72), specifically obese premenopausal women (age < 55 years) (<it>p </it>= 0.011, RR = 1.98).</p> <p>Conclusion</p> <p>OAB prevalence is more than double and higher in men than previously reported. The relative risk for OAB is significantly greater in obese premenopausal women.</p
Search for time-dependent B0s - B0s-bar oscillations using a vertex charge dipole technique
We report a search for B0s - B0s-bar oscillations using a sample of 400,000
hadronic Z0 decays collected by the SLD experiment. The analysis takes
advantage of the electron beam polarization as well as information from the
hemisphere opposite that of the reconstructed B decay to tag the B production
flavor. The excellent resolution provided by the pixel CCD vertex detector is
exploited to cleanly reconstruct both B and cascade D decay vertices, and tag
the B decay flavor from the charge difference between them. We exclude the
following values of the B0s - B0s-bar oscillation frequency: Delta m_s < 4.9
ps-1 and 7.9 < Delta m_s < 10.3 ps-1 at the 95% confidence level.Comment: 18 pages, 3 figures, replaced by version accepted for publication in
Phys.Rev.D; results differ slightly from first versio
Predicting the development of stress urinary incontinence 3Â years after hysterectomy
We aimed to develop a prediction rule to predict the individual risk to develop stress urinary incontinence (SUI) after hysterectomy. Prospective observational study with 3-year follow-up among women who underwent abdominal or vaginal hysterectomy for benign conditions, excluding vaginal prolapse, and who did not report SUI before surgery (n = 183). The presence of SUI was assessed using a validated questionnaire. Significant prognostic factors for de novo SUI were BMI (OR 1.1 per kg/m(2), 95% CI 1.0-1.2), younger age at time of hysterectomy (OR 0.9 per year, 95% CI 0.8-1.0) and vaginal hysterectomy (OR 2.3, 95% CI 1.0-5.2). Using these variables, we developed the following rule to predict the risk of developing SUI: 32 + BMI-age + (7.5 × route of surgery). We defined a prediction rule that can be used to counsel patients about their individual risk on developing SUI following hysterectom
Canalization of Gene Expression and Domain Shifts in the Drosophila Blastoderm by Dynamical Attractors
The variation in the expression patterns of the gap genes in the blastoderm of
the fruit fly Drosophila melanogaster reduces over time as a
result of cross regulation between these genes, a fact that we have demonstrated
in an accompanying article in PLoS Biology (see Manu et al.,
doi:10.1371/journal.pbio.1000049). This biologically essential process is an
example of the phenomenon known as canalization. It has been suggested that the
developmental trajectory of a wild-type organism is inherently stable, and that
canalization is a manifestation of this property. Although the role of gap genes
in the canalization process was established by correctly predicting the response
of the system to particular perturbations, the stability of the developmental
trajectory remains to be investigated. For many years, it has been speculated
that stability against perturbations during development can be described by
dynamical systems having attracting sets that drive reductions of volume in
phase space. In this paper, we show that both the reduction in variability of
gap gene expression as well as shifts in the position of posterior gap gene
domains are the result of the actions of attractors in the gap gene dynamical
system. Two biologically distinct dynamical regions exist in the early embryo,
separated by a bifurcation at 53% egg length. In the anterior region,
reduction in variation occurs because of stability induced by point attractors,
while in the posterior, the stability of the developmental trajectory arises
from a one-dimensional attracting manifold. This manifold also controls a
previously characterized anterior shift of posterior region gap domains. Our
analysis shows that the complex phenomena of canalization and pattern formation
in the Drosophila blastoderm can be understood in terms of the
qualitative features of the dynamical system. The result confirms the idea that
attractors are important for developmental stability and shows a richer variety
of dynamical attractors in developmental systems than has been previously
recognized
Clinical significance of serological biomarkers and neuropsychological performances in patients with temporal lobe epilepsy
<p>Abstract</p> <p>Background</p> <p>Temporal lobe epilepsy (TLE) is a common form of focal epilepsy. Serum biomarkers to predict cognitive performance in TLE patients without psychiatric comorbidities and the link with gray matter (GM) atrophy have not been fully explored.</p> <p>Methods</p> <p>Thirty-four patients with TLE and 34 sex - and age-matched controls were enrolled for standardized cognitive tests, neuroimaging studies as well as measurements of serum levels of heat shock protein 70 (HSP70), S100ß protein (S100ßP), neuronal specific enolase (NSE), plasma nuclear and mitochondrial DNA levels.</p> <p>Results</p> <p>Compared with the controls, the patients with TLE had poorer cognitive performances and higher HSP70 and S100ßP levels (<it>p </it>< 0.01). The patients with higher frequencies of seizures had higher levels of HSP70, NSE and S100ßP (<it>p </it>< 0.01). Serum HSP70 level correlated positively with duration of epilepsy (σ = 0.413, <it>p </it>< 0.01), and inversely with memory scores in the late registration (σ = −0.276, <it>p </it>= 0.01) and early recall score (σ = −0.304, <it>p </it>= 0.007). Compared with the controls, gray matter atrophy in the hippocampal and parahippocampal areas, putamen, thalamus and supplementary motor areas were found in the patient group. The HSP70 levels showed an inverse correlation with hippocampal volume (R square = 0.22, <it>p </it>= 0.007) after controlling for the effect of age.</p> <p>Conclusions</p> <p>Our results suggest that serum biomarkers were predictive of higher frequencies of seizures in the TLE group. HSP70 may be considered to be a stress biomarker in patients with TLE in that it correlated inversely with memory scores and hippocampal volume. In addition, the symmetric extratemporal atrophic patterns may be related to damage of neuronal networks and epileptogenesis in TLE.</p
Study of the reaction e^{+}e^{-} -->J/psi\pi^{+}\pi^{-} via initial-state radiation at BaBar
We study the process with
initial-state-radiation events produced at the PEP-II asymmetric-energy
collider. The data were recorded with the BaBar detector at center-of-mass
energies 10.58 and 10.54 GeV, and correspond to an integrated luminosity of 454
. We investigate the mass
distribution in the region from 3.5 to 5.5 . Below 3.7
the signal dominates, and above 4
there is a significant peak due to the Y(4260). A fit to
the data in the range 3.74 -- 5.50 yields a mass value
(stat) (syst) and a width value (stat)(syst) for this state. We do not
confirm the report from the Belle collaboration of a broad structure at 4.01
. In addition, we investigate the system
which results from Y(4260) decay
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