749 research outputs found
Band splitting and Modal Dispersion induced by Symmetry braking in Coupled-Resonator Slow-Light Waveguide Structures
We study the dispersion relations in slow-light waveguide structures
consisting of coupled microdisk resonators. A group theoretical analysis of the
symmetry properties of the propagating modes reveals an interesting phenomenon:
The degeneracy of the CW and CCW rotating modes is removed, giving rise to two
distinct transmission bands. This effect induces symmetry-based dispersion
which may limit usable bandwidth of such structures. The properties of this
band splitting and its impact on CROW performance for optical communications
are studied in detail
Transmission of Slow Light through Photonic Crystal Waveguide Bends
The spectral dependence of a bending loss of cascaded 60-degree bends in
photonic crystal (PhC) waveguides is explored in a slab-type
silicon-on-insulator system. Ultra-low bending loss of (0.05+/-0.03)dB/bend is
measured at wavelengths corresponding to the nearly dispersionless transmission
regime. In contrast, the PhC bend is found to become completely opaque for
wavelengths range corresponding to the slow light regime. A general strategy is
presented and experimentally verified to optimize the bend design for improved
slow light transmission.Comment: 4 pages, 3 figures; submitted to Optics Letter
Stopping Light All-Optically
We show that light pulses can be stopped and stored all-optically, with a
process that involves an adiabatic and reversible pulse bandwidth compression
occurring entirely in the optical domain. Such a process overcomes the
fundamental bandwidth-delay constraint in optics, and can generate arbitrarily
small group velocities for light pulses with a given bandwidth, without the use
of any coherent or resonant light-matter interactions. We exhibit this process
in optical resonator systems, where the pulse bandwidth compression is
accomplished only by small refractive index modulations performed at moderate
speeds. (Accepted for publication in Phys. Rev. Lett. Submitted on Sept. 10th
2003)Comment: 18 pages including 3 figures. Accepted for publication in Phys. Rev.
Let
The Leu34Phe ProCART Mutation Leads to Cocaine- and Amphetamine-Regulated Transcript (CART) Deficiency: A Possible Cause for Obesity in Humans
Cocaine- and amphetamine-regulated transcript (CART) is an anorexigenic neuropeptide synthesized in the hypothalamus. A Leu34Phe missense mutation in proCART has been found in an obese family in humans. Here we show that humans bearing the Leu34Phe mutation in proCART have severely diminished levels of bioactive CART, but elevated amounts of partially processed proCART in their serum. Expression of wild-type proCART in AtT-20 cells showed that it was sorted to the regulated secretory pathway, a necessity for proper processing to bioactive CART. However, expressed Leu34Phe proCART was missorted, poorly processed, and secreted constitutively. The defective intracellular sorting of Leu34Phe proCART would account for the reduced levels of bioactive CART in affected humans. These results suggest that the obesity observed in humans bearing the Leu34Phe mutation could be due to a putative deficiency in hypothalamic bioactive CART
An analysis of inpatient pediatric sickle cell disease: Incidence, costs, and outcomes
ObjectiveTo identify characteristics of pediatric sickle cell disease (SCD) hospitalizations and to examine admission demographics and medical expenditures.MethodsAdmissions with SCD were identified from the 2009 and 2012 releases of the Healthcare and Cost Utilization Project’s Kids Inpatient Database. Diseaseâ specific secondary diagnoses including acute chest syndrome (ACS), vasoâ occlusive pain crisis (VOC), splenic sequestration, and stroke/transient ischemic attack were analyzed for patient and hospital demographics. Analytical endpoints included total healthcare expenditures and mortality.ResultsWe reviewed 75,234 inpatient hospitalizations with a diagnosis of SCD. Over 18,956), behind ACS ($22,631). A high proportion of Caucasian patients died during hospitalization for VOC (0.4% vs. 0.1%, P = 0.014) and ACS (4% vs. 0.2%, P < 0.001) when compared to nonâ Caucasians.ConclusionInpatient hospitalizations for secondary manifestations of pediatric SCD were associated with significant healthcare expenditures. Patients with an increased statistical risk for death during hospitalization included Caucasians with SCD complications of ACS and VOC, and patients <1â yearâ old with ACS. Further research is needed to substantiate the associated clinical significance of these findings.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140014/1/pbc26758.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/140014/2/pbc26758_am.pd
Observation of a stronger-than-adiabatic change of light trapped in an ultrafast switched GaAs-AlAs microcavity
We study the time-resolved reflectivity spectrum of a switched planar
GaAs-AlAs microcavity. Between 5 and 40 ps after the switching (pump) pulse we
observe a strong excess probe reflectivity and a change of the frequency of
light trapped in the cavity up to 5 linewidths away from the cavity resonance.
This frequency change does not adiabatically follow the fast-changing cavity
resonance. The frequency change is attributed to an accumulated phase change
due to the time-dependent refractive index. An analytical model predicts
dynamics in qualitative agreement with the experiments, and points to crucial
parameters that control future applications.Comment: Discussed effect of probe bandwidth. Included functional forms of
n(z) and R(z
Recent cancer incidence trends in an observational clinical cohort of HIV-infected patients in the US, 2000 to 2011
Abstract Background In HIV-infected populations in developed countries, the most recent published cancer incidence trend analyses are only updated through 2008. We assessed changes in the distribution of cancer types and incidence trends among HIV-infected patients in North Carolina up until 2011. Methods We linked the University of North Carolina Center for AIDS Research HIV Clinical Cohort, an observational clinical cohort of 3141 HIV-infected patients, with the North Carolina Cancer registry. Cancer incidence rates were estimated across calendar years from 2000 to 2011. The distribution of cancer types was described. Incidence trends were assessed with linear regression. Results Across 15,022 person-years of follow-up, 202 cancers were identified (incidence rate per 100,000 person-years [IR]: 1345; 95% confidence interval [CI]: 1166, 1544). The majority of cancers were virus-related (61%), including Kaposi sarcoma (N = 32) (IR: 213; 95%CI: 146, 301), non-Hodgkin lymphoma (N = 34) (IR: 226; 95%CI: 157, 316), and anal cancer (N = 16) (IR: 107; 95%CI: 61, 173). Non-Hodgkin lymphoma was observed to decrease from 2000 to 2011 (decline of 15 cases per 100,000 person-years per calendar year, 95%CI: -27, -3). No other changes in incidence or changes in incidence trends were observed for other cancers (all P > 0.20). Conclusions We observed a substantial burden of a variety of cancers in this population in the last decade. Kaposi sarcoma and non-Hodgkin lymphoma were consistently two of the greatest contributors to cancer burden across calendar time. Cancer rates appeared stable across calendar years, except for non-Hodgkin lymphoma, which appeared to decrease throughout the study period
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The most reactive amide as a transition-state mimic for cis-trans interconversion.
1-Azatricyclo[3.3.1.1(3,7)]decan-2-one (3), the parent compound of a rare class of 90°-twisted amides, has finally been synthesized, using an unprecedented transformation. These compounds are of special interest as transition-state mimics for the enzyme-catalyzed cis-trans rotamer interconversion of amides involved in peptide and protein folding and function. The stabilization of the amide group in its high energy, perpendicular conformation common to both systems is shown for the rigid tricyclic system to depend, as predicted by calculation, on its methyl group substitution pattern, making 3 by some way the most reactive known "amide".Financial assistance from Enamine Ltd. (www.enamine.net) is
gratefully acknowledged. We also thank Dr. V. Stepanenko for
valuable advice and encouragement which helped to find the
nonstandard solutions to the synthetic problems, and Vitaliy
Bilenko for drawing our attention to the instructive EI mass
spectrum of compound 8.This is the final published version of the article, originally published in the Journal of the American Chemical Society, 2015, 137 (2), pp 926–93, DOI: 10.1021/ja511460
The Sagnac effect in Coupled-Resonator Slow-Light Waveguide Structures
We study the effect of rotation on the propagation of electromagnetic waves
in slow-light waveguide structures consisting of coupled micro-ring resonators.
We show that such configurations exhibit new a type of the Sagnac effect which
can be used for the realization of highly-compact integrated rotation sensors
and gyroscopes
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