Quasi-phase-matched grating characterization using minimum-phase functions

Measurement of the second-harmonic power generated by a quasi-phase-matched (QPM) grating as a function of the frequency detuning parameter yields the Fourier transform (FT) magnitude of the complex nonlinear coefficient profile along the QPM device. This FT magnitude can be measured by tuning either the wavelength of the fundamental laser beam or the temperature of the QPM grating. However, the measured magnitude of the FT cannot be unambiguously inverted without the FT phase to uniquely recover the complex nonlinear coefficient profile of the QPM grating. As we demonstrate in this work, this ambiguity can be completely eliminated by placing a stronger and thinner nonlinear sample against the input or output of the QPM device of interest and measuring the detuning curve of this composite structure. By construction, the nonlinear profile of this assembly has a sharp peak due to the thinner sample, followed by the weaker, broader profile of the QPM grating, which essentially constitutes a minimum-phase function. Therefore, its FT phase can be calculated uniquely from its measured FT magnitude, for example by applying to the FT amplitude the logarithmic Hilbert transform or an iterative error-reduction algorithm. This processing then enables the full recovery of the complex nonlinear coefficient profile of the QPM device from its measured detuning curve. In this paper, we demonstrate with numerical examples that this powerful new technique can accurately recover the period, envelope, and chirp parameters of any QPM grating.     

ABC‐type hetero‐arm star terpolymers through “Click” chemistry

Hetero‐arm star ABC‐type terpolymers, poly(methyl methacrylate)‐polystyrene‐poly(tert‐butyl acrylate) (PMMA‐PS‐PtBA) and PMMA‐PS‐poly(ethylene glycol) (PEG), were prepared by using “Click” chemistry strategy. For this, first, PMMA‐b‐PS with alkyne functional group at the junction point was obtained from successive atom transfer radical polymerization (ATRP) and nitroxide‐mediated radical polymerization (NMP) routes. Furthermore, PtBA obtained from ATRP of tBA and commercially available monohydroxyl PEG were efficiently converted to the azide end‐functionalized polymers. As a second step, the alkyne and azide functional polymers were reacted to give the hetero‐arm star polymers in the presence of CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine ( PMDETA) in DMF at room temperature for 24 h. The hetero‐arm star polymers were characterized by ¹H NMR, GPC, and DSC. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5699–5707, 2006     

Chemical modification of silica gel with synthesized new Schiff base derivatives and sorption studies of cobalt (II) and nickel (II)

In this study, three Schiff base ligands and their complexes were synthesized and characterized by infrared spectroscopy (IR), thermogravimetric analyses (TGA), nuclear magnetic resonance (NMR), elemental analysis and magnetic susceptibility apparatuses. Silica gel was respectively modified with Schiff base derivatives, (E)-2-[(2-chloroethylimino)methyl]phenol, (E)-4-[(2-chloroethylimino)methyl]phenol and N,N′-[1,4-phenilendi(E)methylidene]bis(2-chloroethanamine), after silanization of silica gel by (3-aminopropyl)trimethoxysilane (APTS) by using a suitable method. Characterization of the surface modification was also performed with IR, TGA and elemental analysis. The immobilized surfaces were used for Co(II) and Ni(II) sorption from aqueous solutions and values of sorption were detected by atomic absorption spectrometer (AAS).     

Large Buffer Asymptotics for Fluid Queues with Heterogeneous M/G/∞ Weibullian Inputs

In this paper we consider a generalization of the so called M/G/ model where M types of sessions enter a buffer. The instantaneous rates of the sessions are functions of the occupancy of an M/G/ system with Weibullian G distributions. In particular we assume that a session of type i transmits r _i cells per unit time and lasts for a random time with a Weibull distribution given by x) \sim {\text{e}}^{{\text{ - }}\gamma ix^{\alpha i} } $$ " align="middle" border="0"> , where 0< _i <1, _i >0. We show that the complementary buffer occupancy distribution for large buffer size is Weibullian whose parameters can be determined as the solution of a deterministic nonlinear knapsack problem. For _i <0.5, upper and lower bound factors are determined. When specialized to the homogeneous case, i.e., when all the sessions are identical, the result coincides with a lower bound reported in the literature.     

Crystal structure of 2,2-dimethyl succinic acid.

The title compound crystallizes triclinically in space group of P1. The C2-COOH and C3-COOH molecular groups are planar. The crystal structure is stabilized by the formation of intermolecular (O-HO) hydrogen bonds.     

Trends in labor efficiency among American hospital markets

The health care sector is one of the most labor intensive sectors of the economy. As a major player in health service delivery, hospitals must closely examine their largest cost — labor expenses. This study evaluates trends in the efficiency of health care labor among urban hospital markets. More specifically, it assesses the hypothesis that technological changes and market and regulatory pressures have increased aggregate labor efficiency. Using data envelopment analysis (DEA), this study evaluates labor efficiency in 1989 and 1993 in 298 metropolitan statistical areas (MSAs) with two or more hospitals. Results of this study suggest that between 1989 and 1993, hospital markets generally demonstrated higher labor inefficiencies. The U.S. health care system could save approximately $16.6 billion in 1993 by eliminating hospitals' excessive use of health care provider labor.     

Rewritable self-assembled long-period gratings in photonic bandgap fibers using microparticles

We report the demonstration of rewritable self-assembled long-period gratings in air-core photonic bandgap fibers. The long-period gratings are written by filling the air-core region of the fiber with a solution containing polystyrene microspheres. The microspheres are self-assembled into a periodic structure as the liquid inside the fiber evaporates, forming the long-period grating. The formed grating can then be easily erased for rewriting purposes by connecting the end of the fiber to a microfluidic pump through a microfluidic channel and washing out the microparticles with an appropriate liquid. The same microfluidic system can also be used to fine control the writing process of the gratings. This technique creates possibilities for writing various different filtering functions in air-core photonic bandgap fibers by varying the composition and/or the shape of the used microparticles. The presented technique is potentially applicable to solid-core photonic crystal fibers as well.     

Holographic pixel super-resolution in portable lensless on-chip microscopy using a fiber-optic array

We report a portable lensless on-chip microscope that can achieve <1 μm resolution over a wide field-of-view of ～ 24 mm(2) without the use of any mechanical scanning. This compact on-chip microscope weighs ～ 95 g and is based on partially coherent digital in-line holography. Multiple fiber-optic waveguides are butt-coupled to light emitting diodes, which are controlled by a low-cost micro-controller to sequentially illuminate the sample. The resulting lensfree holograms are then captured by a digital sensor-array and are rapidly processed using a pixel super-resolution algorithm to generate much higher resolution holographic images (both phase and amplitude) of the objects. This wide-field and high-resolution on-chip microscope, being compact and light-weight, would be important for global health problems such as diagnosis of infectious diseases in remote locations. Toward this end, we validate the performance of this field-portable microscope by imaging human malaria parasites (Plasmodium falciparum) in thin blood smears. Our results constitute the first-time that a lensfree on-chip microscope has successfully imaged malaria parasites.     

Wide-field lensless fluorescent microscopy using a tapered fiber-optic faceplate on a chip

We demonstrate lensless fluorescent microscopy over a large field-of-view of ~60 mm(2) with a spatial resolution of <4 μm. In this on-chip fluorescent imaging modality, the samples are placed on a fiber-optic faceplate that is tapered such that the density of the fiber-optic waveguides on the top facet is >5 fold larger than the bottom one. Placed on this tapered faceplate, the fluorescent samples are pumped from the side through a glass hemisphere interface. After excitation of the samples, the pump light is rejected through total internal reflection that occurs at the bottom facet of the sample substrate. The fluorescent emission from the sample is then collected by the smaller end of the tapered faceplate and is delivered to an opto-electronic sensor-array to be digitally sampled. Using a compressive sampling algorithm, we decode these raw lensfree images to validate the resolution (<4 μm) of this on-chip fluorescent imaging platform using microparticles as well as labeled Giardia muris cysts. This wide-field lensfree fluorescent microscopy platform, being compact and high-throughput, might provide a valuable tool especially for cytometry, rare cell analysis (involving large area microfluidic systems) as well as for microarray imaging applications.