383 research outputs found
High Power Solid State Retrofit Lamp Thermal Characterization and Modeling
Thermal and thermo-mechanical modeling and characterization of solid state lightening (SSL) retrofit LED lamp are presented in this paper. Paramount importance is to design SSL lamps for reliability, in which thermal and thermo-mechanical aspects are key points. The main goal is to get a precise 3D thermal lamp model for further thermal optimization. Simulations are performed with ANSYS and CoventorWare software tools to compere different simulation approaches. Simulated thermal distribution has been validated with thermal measurement on a commercial 8W LED lamp. Materials parametric study has been carried out to discover problematic parts for heat transfer from power LEDs to ambient and future solutions are proposed. The objectives are to predict the thermal management by simulation of LED lamp, get more understanding in the effect of lamp shape and used materials in order to design more effective LED lamps and predict light quality, life time and reliability
Local recovery of cardiac calcium‐induced calcium release interrogated by ultra‐effective, two‐photon uncaging of calcium
KEY POINTS: In cardiac myocytes, subcellular local calcium release signals, calcium sparks, are recruited to form each cellular calcium transient and activate the contractile machinery. Abnormal timing of recovery of sparks after their termination may contribute to arrhythmias. We developed a method to interrogate recovery of calcium spark trigger probabilities and their amplitude over time using two‐photon photolysis of a new ultra‐effective caged calcium compound. The findings confirm the utility of the technique to define an elevated sensitivity of the calcium release mechanism in situ and to follow hastened recovery of spark trigger probabilities in a mouse model of an inherited cardiac arrhythmia, which was used for validation. Analogous methods are likely to be applicable to investigate other microscopic subcellular signalling systems in a variety of cell types. ABSTRACT: In cardiac myocytes Ca(2+)‐induced Ca(2+) release (CICR) from the sarcoplasmic reticulum (SR) through ryanodine receptors (RyRs) governs activation of contraction. Ca(2+) release occurs via subcellular Ca(2+) signalling events, Ca(2+) sparks. Local recovery of Ca(2+) release depends on both SR refilling and restoration of Ca(2+) sensitivity of the RyRs. We used two‐photon (2P) photolysis of the ultra‐effective caged Ca(2+) compound BIST‐2EGTA and laser‐scanning confocal Ca(2+) imaging to probe refractoriness of local Ca(2+) release in control conditions and in the presence of cAMP or low‐dose caffeine (to stimulate CICR) or cyclopiazonic acid (CPA; to slow SR refilling). Permeabilized cardiomyocytes were loaded with BIST‐2EGTA and rhod‐2. Pairs of short 2P photolytic pulses (1 ms, 810 nm) were applied with different intervals to test Ca(2+) release amplitude recovery and trigger probability for the second spark in a pair. Photolytic and biological events were distinguished by classification with a self‐learning support vector machine (SVM) algorithm. In permeabilized myocytes data recorded in the presence of CPA showed a lower probability of triggering a second spark compared to control or cAMP conditions. Cardiomyocytes from a mouse model harbouring the arrhythmogenic RyR(R420Q) mutation were used for further validation and revealed a higher Ca(2+) sensitivity of CICR. This new 2P approach provides composite information of Ca(2+) release amplitude and trigger probability recovery reflecting both SR refilling and restoration of CICR and RyR Ca(2+) sensitivity. It can be used to measure the kinetics of local CICR recovery, alterations of which may be related to premature heart beats and arrhythmias
Strain Modulation of Graphene by Nanoscale Substrate Curvatures: A Molecular View
Spatially nonuniform strain is important for engineering the pseudomagnetic
field and band structure of graphene. Despite the wide interest in strain
engineering, there is still a lack of control on device-compatible strain
patterns due to the limited understanding of the structure-strain relationship.
Here, we study the effect of substrate corrugation and curvature on the strain
profiles of graphene via combined experimental and theoretical studies of a
model system: graphene on closely packed SiO2 nanospheres with different
diameters (20-200 nm). Experimentally, via quantitative Raman analysis, we
observe partial adhesion and wrinkle features and find that smaller nanospheres
induce larger tensile strain in graphene, theoretically, molecular dynamics
simulations confirm the same microscopic structure and size dependence of
strain and reveal that a larger strain is caused by a stronger, inhomogeneous
interaction force between smaller nanospheres and graphene. This
molecular-level understanding of the strain mechanism is important for strain
engineering of graphene and other two-dimensional materials.Comment: Nano Letters (2018
Observation of the Dynamic Beta Effect at CESR with CLEO
Using the silicon strip detector of the CLEO experiment operating at the
Cornell Electron-positron Storage Ring (CESR), we have observed that the
horizontal size of the luminous region decreases in the presence of the
beam-beam interaction from what is expected without the beam-beam interaction.
The dependence on the bunch current agrees with the prediction of the dynamic
beta effect. This is the first direct observation of the effect.Comment: 9 page uuencoded postscript file, postscritp file also available
through http://w4.lns.cornell.edu/public/CLNS, submitted to Phys. Rev.
First Observation of
We report on a study of exclusive radiative decays of the Upsilon(1S)
resonance collected with the CLEO-II detector operating at CESR. We present the
first observation of the radiative decays Upsilon(1S)->gamma pi+pi- and
Upsilon(1S)->gamma pi0pi0. For the dipion mass regime m(pipi)>1.0 GeV, we
obtain Br(Upsilon(1S)->gamma pi+pi-=(6.3+/-1.2+/-1.3) x 10^(-5), and
Br(Upsilon(1S)->gamma pi0pi0=(1.7+/-0.6+/-0.3) x 10^(-5). The observed gamma
pipi events are consistent with the hypothesis Upsilon(1S)->gamma f2(1270).Comment: 9 pages, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
Flavor-Specific Inclusive B Decays to Charm
We have measured the branching fractions for B -> D_bar X, B -> D X, and B ->
D_bar X \ell^+ \nu, where ``B'' is an average over B^0 and B^+, ``D'' is a sum
over D^0 and D^+, and``D_bar'' is a sum over D^0_bar and D^-. From these
results and some previously measured branching fractions, we obtain Br(b -> c
c_bar s) = (21.9 3.7)%, Br(b -> s g) K^-
\pi^+) = (3.69 0.20)%. Implications for the ``B semileptonic decay
problem'' (measured branching fraction being below theoretical expectations)
are discussed. The increase in the value of Br(b -> c c_bar s) due to eliminates 40% of the discrepancy.Comment: 12 page postscript file, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
Radiative Decay Modes of the Meson
Using data recorded by the CLEO-II detector at CESR we have searched for four
radiative decay modes of the meson: ,
, , and . We
obtain 90% CL upper limits on the branching ratios of these modes of , , and
respectively.Comment: 15 page postscript file, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
Tau Neutrino Helicity from Energy Correlations
We report a measurement of the magnitude of the tau neutrino helicity from
tau-pair events taken with the CLEO detector at the CESR electron-positron
storage ring. Events in which each tau undergoes the decay tau -> h nu, with h
a charged pion or kaon, are analyzed for energy correlations between the
daughter hadrons, yielding |xi| = 2*|h_nu| = 1.03 +/- 0.06 +/- 0.04, with the
first error statistical and the second systematic.Comment: 11 pages, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
Measurement of using Partila Reconstruction of
We present a measurement of the absolute branching fraction for using the reconstruction of the decay chain , where only the lepton and the low-momentum pion from
the are detected. With data collected by the CLEO II detector at the
Cornell Electron Storage Ring, we have determined .Comment: 10 page postscript file, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
Limit on the Two-Photon Production of the Glueball Candidate at CLEO
We use the CLEO detector at the Cornell electron-positron storage ring, CESR,
to search for the two-photon production of the glueball candidate f_J(2220) in
its decay to K_s K_s. We present a restrictive upper limit on the product of
the two-photon partial width and the K_s K_s branching fraction. We use this
limit to calculate a lower limit on the stickiness, which is a measure of the
two-gluon coupling relative to the two-photon coupling. This limit on
stickiness indicates that the f_J(2220) has substantial glueball content.Comment: 9 page postscript file, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
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