Vertical InGaN Light-Emitting Diode with Hybrid Distributed Bragg Reflectors.

A vertical-type InGaN light-emitting diode with a resonant cavity was demonstrated with a 9 μm aperture size and a short cavity formed by hybrid distributed Bragg reflectors (DBRs). The approach involved designing epitaxial structures and utilizing an electrochemical etching process to convert heavily doped n-type gallium nitride (n-GaN) layers into porous GaN layers as a porous-GaN DBR structure. Thirteen pairs of the conductive porous-GaN:Si/GaN:Si DBR structure provided a vertical current path in a vertical-type light-emitting diodes (LED) structure.

Anisotropic properties of pipe-GaN distributed Bragg reflectors.

We report here a simple and robust process to convert periodic Si-doped GaN/undoped-GaN epitaxial layers into a porous-GaN/u-GaN distributed Bragg reflector (DBR) structure and demonstrate its material properties in a high-reflectance epitaxial reflector. Directional pipe-GaN layers with anisotropic optical properties were formed from n-GaN : Si layers in a stacked structure through a lateral and doping-selective electrochemical etching process. Central wavelengths of the polarized reflectance spectra were measured to be 473 nm and 457 nm for the pipe-GaN reflector when the direction of the linear polarizer was along and perpendicular to the pipe-GaN structure.

Weak Gravity Conjecture from Unitarity and Causality.

The weak gravity conjecture states that quantum gravity theories have to contain a charged state with a charge-to-mass ratio bigger than unity. By studying unitarity and causality constraints on higher derivative corrections to the charge-to-mass ratio of extremal back holes, we demonstrate that heavy extremal black holes can play the role of the required charged state under several assumptions. In particular, our argument is applicable when the higher-spin states Reggeizing graviton exchange are subdominant in the photon scattering.

Infinite Set of Soft Theorems in Gauge-Gravity Theories as Ward-Takahashi Identities.

We show that the soft photon, gluon, and graviton theorems can be understood as the Ward-Takahashi identities of large gauge transformation, i.e., diffeomorphism that does not fall off at spatial infinity.

Gravitational Waves from Oscillons with Cuspy Potentials.

We study the production of gravitational waves during oscillations of the inflaton around the minimum of a cuspy potential after inflation. We find that a cusp in the potential can trigger copious oscillon formation, which sources a characteristic energy spectrum of gravitational waves with double peaks. The discovery of such a double-peak spectrum could test the underlying inflationary physics.

InGaN Light-Emitting Diodes with an Embedded Nanoporous GaN Distributed Bragg Reflectors.

InGaN light emitting diodes (LED) structure with an embedded 1/4λ-stack nanoporous-GaN/undoped-GaN distributed Bragg reflectors (DBR) structure have been demonstrated. Si-heavily doped GaN epitaxial layers (n(+)-GaN) in the 12-period n(+)-GaN/u-GaN stack structure are transformed into low refractive index nanoporous GaN structure through the doping-selective electrochemical wet etching process. The central wavelength of the nanoporous DBR structure was located at 442.

Widening the Axion Window via Kinetic and Stückelberg Mixings.

We point out that kinetic and Stückelberg mixings that are generically present in the low energy effective action of axions can significantly widen the window of axion decay constants. We show that an effective super-Planckian decay constant can be obtained even when the axion kinetic matrix has only sub-Planckian entries. Our minimal model involves only two axions, a Stückelberg U(1) and a modest rank instanton generating non-Abelian group.

Probing hidden sectors with Stückelberg U(1) gauge fields.

We propose a framework in which visible matter interacts with matter from a hidden sector through mass mixings of Stückelberg U(1) gauge fields. In contrast to other Z(') mediation scenarios, our setup has the added appealing features that (i) the choice of Z(')'s can be significantly broadened without necessarily introducing unwanted exotic matter and (ii) there can be sizable tree-level interactions between the visible and hidden sectors. String theory embeddings of this scenario and their phenomenological features are briefly discussed.

ADI1, a methionine salvage pathway enzyme, is required for Drosophila fecundity.

Background: Methionine, an essential amino acid, is required for protein synthesis and normal cell metabolism. The transmethylation pathway and methionine salvage pathway (MTA cycle) are two major pathways regulating methionine metabolism. Recently, methionine has been reported to play a key role in Drosophila fecundity.

Millicharged dark matter in quantum gravity and string theory.

We examine the millicharged dark matter scenario from a string theory perspective. In this scenario, kinetic and mass mixings of the photon with extra U(1) bosons are claimed to give rise to small electric charges, carried by dark matter particles, whose values are determined by continuous parameters of the theory. This seems to contradict folk theorems of quantum gravity that forbid the existence of irrational charges in theories with a single massless gauge field.

Wavelet-based method for time-domain noise analysis and reduction in a frequency-scan ion trap mass spectrometer.

We adopt an orthogonal wavelet packet decomposition (OWPD) filtering approach to cancel harmonic interference noises arising from an AC power source in time domain and remove the resulting rf voltage interference noise from the mass spectra acquired by using a charge detection frequency-scan quadrupole ion trap mass spectrometer. With the use of a phase lock resampling technique, the transform coefficients of the rf interference in signals become a constant, exhibiting a shift of the baseline in different rf phases. The rf interference is therefore removable by shifting the baselines back to zero in OWPD coefficients.

Probing the geometry of warped string compactifications at the Large Hadron Collider.

Warped string compactifications, characterized by the nonsingular behavior of the metric in the infrared (IR), feature departures from the usual anti-de Sitter warped extra dimensions. We study the implications of the smooth IR cutoff for Randall-Sundrum- (RS-)type models. We find that the phenomenology of the Kaluza-Klein gravitons (including their masses and couplings) depends sensitively on the precise shape of the warp factor in the IR.

Vacuum sampling in the landscape during inflation.

We consider the phenomenological consequences of sampling multiple vacua during inflation motivated by an enormous landscape. A generic consequence of this sampling is the formation of domain walls, characterized by the scale mu of the barriers that partition the accessed vacua. We find that the success of big bang nucleosynthesis (BBN) implies mu > or = 10 TeV, as long as the sampled vacua have a nondegeneracy larger than O(MeV4).

Observing the geometry of warped compactification via cosmic inflation.

Using Dirac-Born-Infeld inflation as an example, we demonstrate that the detailed geometry of warped compactification can leave an imprint on the cosmic microwave background. We compute cosmic microwave background observables for Dirac-Born-Infeld inflation in a generic class of warped throats and find that the results (such as the sign of the tilt of the scalar perturbations and its running) depend sensitively on the precise shape of the warp factor. In particular, we analyze the warped deformed conifold and find that the results can differ from those of other warped geometries, even when these geometries approximate well the exact metric of the warped deformed conifold.

Three-family supersymmetric standardlike models from intersecting brane worlds.

We construct the first three family N = 1 supersymmetric string model with standard model gauge group SU(3)(C) x SU(2)(L) x U(1)(Y) from an orientifold of type IIA theory on T(6)/(Z(2) x Z(2)) and D6-branes intersecting at angles. In addition to the minimal supersymmetric standard model particles, the model contains right-handed neutrinos, a chiral (but anomaly-free) set of exotic multiplets, and extra vectorlike multiplets. We discuss some phenomenological features of this model.

Determination of ginsenosides in plant extracts from Panax ginseng and Panax quinquefolius L. by LC/MS/MS.

An HPLC/MS/MS method has been developed for the characterization and quantification of ginsenosides contained in extracts of the root of Panax ginseng (Korean ginsengs) and Panax quinquefolius L. (American ginsengs). The [M + H]+ and [M + Na]+ ions were observed for ginsenoside standards (Rb1, Rb2, Rc, Rd, Re, Rf, Rg1) and four different ginseng extracts.

Solid-phase extraction-high-performance liquid chromatography determination of verapamil and norverapamil enantiomers in urine.

A simple, rapid, sensitive and selective method has been developed for the stereospecific determination of verapamil and its metabolite, norverapamil in urine. For sample preparation we utilized a membrane-based solid-phase extraction (SPE) disk consisting of a thin, particle-loaded membrane inserted in a plastic syringe-like barrel. The particles, which may be C8 or C18 bonded phase (C8 in this work), are embedded within a matrix of PTFE (Teflon) fibrils.

Resolution of the enantiomers of ibuprofen; comparison study of diastereomeric method and chiral stationary phase method.

In this study, an indirect diastereomeric method and a direct method utilizing a chiral stationary phase (CSP) were investigated for the resolution of ibuprofen enantiomers. In the indirect method, ethylchloroformate (ECF) and 2-ethoxy-1-1-ethoxycarbonyl-1,2-dihydroquinoline (EEDQ) were utilized as first-step derivatizing reagents in acetonitrile or toluene. In the direct CSP method, ibuprofen enantiomers were derivatized to p-nitrobenzyl ureides and then resolved on an (R)-(-)-(1-naphthyl)ethylurea CSP column.

Switching-valve--filter technique for the direct injection and analysis of drugs in plasma using high-performance liquid chromatography.

An automated technique involving switching valves and a filter assembly has been developed and evaluated for the on-line precipitation of proteins and peptides from plasma samples. In the set-up, the proteins were precipitated on-line by injecting the plasma sample into a stream of organic precipitating agent. The precipitates so formed are filtered on-line by a set of filter assemblies consisting of ordinary in-line HPLC solvent filters.

Reduced bioavailability of moisture-exposed carbamazepine resulting in status epilepticus.

A 28-year-old man with seizures well controlled with carbamazepine (CBZ) and valproate (VPA) developed generalized convulsive status epilepticus three days after his CBZ tablets became wet during a rainstorm while he was camping out. He continued the CBZ but avoided ingesting obviously disintegrating tablets. The VPA was not exposed to excessive moisture.

Effects of humidity and temperature on in vitro dissolution of carbamazepine tablets.

The rate and extent of dissolution of various approved marketed carbamazepine (CBZ) tablets exposed to 33, 52, 75, and 97% relative humidities at both room temperature and 40 degrees C, and saturated water vapor at room temperature were compared to fresh unstressed tablets. The dissolution data indicate that exposure of CBZ tablets to high humidity and temperature can have a profound effect on tablet disintegration and dissolution. The dissolution rates of some batches of CBZ products exposed to 97% humidity at 40 degrees C or saturated water vapor at room temperature were drastically reduced in only 6-7 days.

Determination of khellin in serum by gas chromatography.

A rapid gas chromatographic assay has been developed for the separation and determination of khellin in human serum. Using a DB-17 capillary column and a simple chloroform extraction, khellin and an internal standard, trioxsalen, were separated from endogenous substances without further clean-up. Spiked serum samples in the range 0.

In vitro/in vivo correlations in biopharmaceutics: scientific and regulatory implications.

This paper explains the regulatory and scientific reasons for the regulatory authorities employing dissolution as a key variable for regulatory approval of batch to batch bioequivalence assurance, site of manufacture change, formulation changes, and batch size scale-up for immediate release dosage forms. It also explains the scientific and regulatory reasons why either an in vivo/in vitro correlation using USP's Level 'A', 'B' or 'C', or a newly proposed 'mapping' approach will be required for allowing such changes for controlled-release dosage forms.

In vitro release of nitroglycerin from topical products by use of artificial membranes.

An in vitro testing method for measuring the release of nitroglycerin from topical drug products was evaluated. The method involved measuring the amount of nitroglycerin that diffused from ointments and patches through various synthetic membranes into receptor fluid contained in a modified Franz diffusion cell. Plots of the amount of nitroglycerin released against the square root of time for all 10 synthetic membranes were linear.