Log-concavity of characteristic polynomials and the Bergman fan of matroids

In a recent paper, the first author proved the log-concavity of the coefficients of the characteristic polynomial of a matroid realizable over a field of characteristic 0, answering a long-standing conjecture of Read in graph theory. We extend the proof to all realizable matroids, making progress towards a more general conjecture of Rota?CHeron?CWelsh. Our proof follows from an identification of the coefficients of the reduced characteristic polynomial as answers to particular intersection problems on a toric variety. The log-concavity then follows from an inequality of Hodge type.     

Spectroscopic identification of benzyl-type radicals generated by corona discharge of 2-chloro-4-fluorotoluene

By means of a technique of corona excited supersonic expansion coupled with a pinhole-type glass nozzle, we generated vibronically excited but jet-cooled benzyl-type radicals from precursor 2-chloro-4-fluorotoluene seeded in a large amount of inert carrier gas He. From an analysis of the visible vibronic emission spectrum, we found evidence of the formation of the 2-chloro-4-fluorobenzyl and 4-fluorobenzyl radicals. A possible pathway for the formation of these benzyl-type radicals is herein proposed. Also, the electronic energy in the D(1) → D(0) transition and the vibrational mode frequencies of the 2-chloro-4-fluorobenzyl radical in the ground electronic state were accurately determined, for the first time, by comparison with ab initio calculations and the known vibrational data of the precursor.     

Adding visualization functions of DAVIS to Jasp: Mixing two Java-based statistical systems

Summary  Jasp is an experimental general purpose Java-based statistical system which adopts several new computing technologies. It has a function-based and object-oriented language, an advanced user interface, flexible extensibility and a server/client architecture with distributed computing abilities. DAVIS is, on the other hand, a stand-alone Java-based system, and is designed for providing advanced data visualization functions with easy operations by a GUI. In this paper, it is made possible to use tools of DAVIS from within Jasp, in order that the new integrated system can handle not only data filtering and statistical analysis but also data visualization. We develop a mechanism for extending the server/client system of Jasp to realize an efficient collaboration with DAVIS in the client-side. It is shown that the mechanism is straightforward and simple.     

Minimizing flow time in cyclic schedules for identical jobs with acyclic precedence: the bottleneck lower bound

This paper studies minimizing the flow time of a cyclic schedule for repeated identical jobs, where one job is started/completed in each cycle, subject to the schedule achieving maximum throughput. We propose a branch and bound method for a single machine problem, and use this method to derive an improved lower bound for the multiple machine problem.     

Regulation of glutamate level in rat brain through activation of glutamate dehydrogenase by Corydalis ternata

When treated with protopine and alkalized extracts of the tuber of Corydalis ternata for one year, significant decrease in glutamate level and increase in glutamate dehydrogenase (GDH) activity was observed in rat brains. The expression of GDH between the two groups remained unchanged as determined by Western and Northern blot analysis, suggesting a post-translational regulation of GDH activity in alkalized extracts treated rat brains. The stimulatory effects of alkalized extracts and protopine on the GDH activity was further examined in vitro with two types of human GDH isozymes, hGDH1 (house-keeping GDH) and hGDH2 (nerve-specific GDH). Alkalized extracts and protopine activated the human GDH isozymes up to 4.8-fold. hGDH2 (nerve- specific GDH) was more sensitively affected by 1 mM ADP than hGDH1 (house-keeping GDH) on the activation by alkalized extracts. Studies with cassette mutagenesis at ADP-binding site showed that hGDH2 was more sensitively regulated by ADP than hGDH1 on the activation by Corydalis ternata. Our results suggest that prolonged exposure to Corydalis ternata may be one of the ways to regulate glutamate concentration in brain through the activation of GDH.     

Microfluidic cell disruption system employing a magnetically actuated diaphragm

A microfluidic cell lysis chip equipped with a micromixer and SPE unit was developed and used for quantitative analysis of intracellular proteins. This miniaturized sample preparation system can be employed for any purpose where cell disruption is needed to obtain intracellular constituents for the subsequent analysis. This system comprises a magnetically actuated micromixer to disrupt cells, a hydrophobic valve to manipulate the cell lysate, and a packed porous polymerized monolith chamber for SPE and filtering debris from the cell lysate. Using recombinant Escherichia coli expressing intracellular enhanced green fluorescent protein (EGFP) and lipase as model bacteria, we optimized the cell disruption condition with respect to the lysis buffer composition, mixing time, and the frequency of the diaphragm in the micromixer, which was magnetically actuated by an external magnetic stirrer in the micromixer chamber. The lysed sample prepared under the optimal condition was purified by the packed SPE in the microfluidic chip. At a frequency of 1.96 Hz, the final cell lysis efficiency and relative fluorescence intensity of EGFP after the cell disruption process were greater than 90 and 94%, respectively. Thus, this microfluidic cell disruption chip can be used for the efficient lysis of cells for further analysis of intracellular contents in many applications.     

A Dipolar Anthracene Dye: Synthesis,Optical Properties and Two‐photon Tissue Imaging

Two‐photon microscopy is a powerful tool for studying biological systems. In search of novel two‐photon absorbing dyes for bioimaging, we synthesized a new anthracene‐based dipolar dye (anthradan) and evaluated its two‐photon absorbing and imaging properties. The new anthradan, 9,10‐bis(o‐dimethoxy‐phenyl)‐anthradan, absorbs and emits at longer wavelengths than acedan, a well‐known two‐photon absorbing dye. It is also stable under two‐photon excitation conditions and biocompatible, and thus used for two‐photon imaging of mouse organ tissues to show bright, near‐red fluorescence along with negligible autofluorescence. Such an anthradan thus holds promise as a new class of two‐photon absorbing dyes for the development of fluorescent probes and tags for biological systems.     

Polymeric photoacid generators for direct photochemical modification of surface

To achieve easy spin coating and enhanced efficiency in the photolithographic process for the direct photochemical modification of surface, we incorporated photoacid generator (PAG) into polymer backbone. Bis‐(4‐hydroxy‐phenyl)‐(4‐methoxy‐3,5‐dimethyl‐phenyl)‐sulfonium chloride was synthesized as a monomer, and was polymerized with sebacoyl chloride and terephthaloyl chloride. The resulting polymeric PAG in chloride salt form was converted to the p‐toluenesulfonate and 1‐naphthol‐5‐sulfonate forms with ion‐exchange reactions. By the photolithographic process with the polymeric PAG, the protecting groups of the linker molecules self‐assembled onto a glass plate were micropatterned to produce an amine pattern for the microarray of oligonucleotides. The acids generated from the polymeric PAG effectively deprotect the acid‐labile protecting groups of the linker molecules through a chemical amplification process in the exposed region. After the treatment of the patterned amino groups with a fluorescent dye, the pattern profiles were observed with a fluorescence scanner. The fluorescence image reveals a well‐defined pattern at a micro level, which clearly indicates that the polymeric PAGs have a great potential in photochemical surface modification for the microarray of oligonucleotides. Copyright © 2007 John Wiley & Sons, Ltd.