1,093 research outputs found
The tensor reduction and master integrals of the two-loop massless crossed box with light-like legs
The class of the two-loop massless crossed boxes, with light-like external
legs, is the final unresolved issue in the program of computing the scattering
amplitudes of 2 --> 2 massless particles at next-to-next-to-leading order.
In this paper, we describe an algorithm for the tensor reduction of such
diagrams. After connecting tensor integrals to scalar ones with arbitrary
powers of propagators in higher dimensions, we derive recurrence relations from
integration-by-parts and Lorentz-invariance identities, that allow us to write
the scalar integrals as a combination of two master crossed boxes plus
simpler-topology diagrams.
We derive the system of differential equations that the two master integrals
satisfy using two different methods, and we use one of these equations to
express the second master integral as a function of the first one, already
known in the literature. We then give the analytic expansion of the second
master integral as a function of epsilon=(4-D)/2, where D is the space-time
dimension, up to order O(epsilon^0).Comment: 30 pages, 5 figure
Competitive Advantage from the World Wide Web
Research has suggested that organizations implement World Wide Web sites in order to gain competitive advantage. This research-in-progress uses CAPITA, an instrument for measuring competitive advantage, to determine how organizations seek to use the Web for competitive advantage and how well they succeed
Covalently immobilized porphyrins as photooxidation catalysts
Porphyrins covalently linked to aminomethylated Merrifield polymers, by chlorosulfonation activation of the porphyrin nucleus, are able to generate singlet oxygen with an efficiency which is related to the spacer between porphyrin and the polymer backbone. Juglone and ascaridole are efficiently produced in the presence of these supported catalysts.http://www.sciencedirect.com/science/article/B6THR-4NTRT0M-7/1/c9bc37705a3639162941e23c9c85343
Silica grafted polyethylenimine as heterogeneous catalyst for condensation reactions
Primary amine groups were attached to a silica surface by using α,ω-diamines derivatives
and (3-glycidyloxypropyl)-trimethoxysilane activation. The same activation was used to
graft polyethylenimine, which also contains secondary and tertiary amine groups. These
silica aminated structures were tested as heterogeneous catalysts in nitroaldol
condensation with nitromethane, the derivative with the polyethylenimine moiety being
the more active catalyst. This catalyst also showed efficiency in the Knoevenagel
condensation of benzaldehydes with ethyl cyanoacetate under very mild reaction
conditions and showed much the same efficiency when used in consecutive reaction runs.
A reaction mechanism with participation of the several amine groups of the catalysts is
discussed
In Vitro and In Vivo Studies of Triacetone Triperoxide (TATP) Metabolism in Humans
Purpose
Triacetone triperoxide (TATP) is a volatile but powerful explosive that appeals to terrorists due to its ease of synthesis from household items. For this reason, bomb squad, canine (K9) units, and scientists must work with this material to mitigate this threat. However, no information on the metabolism of TATP is available. Methods
In vitro experiments using human liver microsomes and recombinant enzymes were performed on TATP and TATP-OH for metabolite identification and enzyme phenotyping. Enzyme kinetics for TATP hydroxylation were also investigated. Urine from laboratory personnel collected before and after working with TATP was analyzed for TATP and its metabolites. Results
While experiments with flavin monooxygenases were inconclusive, those with recombinant cytochrome P450s (CYPs) strongly suggested that CYP2B6 was the principle enzyme responsible for TATP hydroxylation. TATP-O-glucuronide was also identified and incubations with recombinant uridine diphosphoglucuronosyltransferases (UGTs) indicated that UGT2B7 catalyzes this reaction. Michaelis–Menten kinetics were determined for TATP hydroxylation, with Km = 1.4 µM and Vmax = 8.7 nmol/min/nmol CYP2B6. TATP-O-glucuronide was present in the urine of all three volunteers after being exposed to TATP vapors showing good in vivo correlation to in vitro data. TATP and TATP-OH were not observed. Conclusions
Since scientists working to characterize and detect TATP to prevent terrorist attacks are constantly exposed to this volatile compound, attention should be paid to its metabolism. This paper is the first to elucidate some exposure, metabolism and excretion of TATP in humans and to identify a marker of TATP exposure, TATP-O-glucuronide in urine
Nomenclature of grapevine leafroll-associated putative closteroviruses
Comparative immunoenzymatic (ELISA), immunoelectron microscopic (IEM) and immunoblotting tests were carried out with antisera produced in different laboratories and commercial diagnostic kits on closterolike viruses reported in the literature under the name of grapevine corky bark-associated virus (GCBaV) and grapevine leafroll-associated viruses IIa and IIb (GLRaV IIa and GLRaV IIb). The results of these studies have established that GCBaV is the same as GLRaV IIb and that both viruses are apparently identical to an isolate of GLRaV-2 identified in France, whose designation as the authentic GLRaV 2 is proposed. GLRaV IIa is serologically distinct from all known clostero-like viruses of the grapevine and, therefore, the provisional name of grapevine leafroll-associated Virus 6 (GLRaV-6) is suggested for it
Perturbative QCD at High Energy Colliders
Selected applications of perturbative Quantumchromodynamics (QCD) to
predictions of the Standard Model for processes at high energy colliders are
reviewed with emphasis on past successes and future problems. This is a
personal retrospective is not intended to be a comprehensive review of the
field.Comment: 18 pages, 12 figures, contribution to the Symposium: 50+ Years of
High Energy Physics at UB, University at Buffalo, October 20-21, 2006. Added
references in section
Imaging extrasolar planets by stellar halo suppression in separately-corrected color bands
Extra-solar planets have not been imaged directly with existing ground or
space telescopes because they are too faint to be seen against the halo of the
nearby bright star. Most techniques being explored to suppress the halo are
achromatic, with separate correction of diffraction and wavefront errors.
Residual speckle structure may be subtracted by differencing images taken
through narrowband filters, but photon noise remains and ultimately limits
sensitivity. Here we describe two ways to take advantage of narrow bands to
reduce speckle photon flux and to obtain better control of systematic errors.
Multiple images are formed in separate color bands of 5-10% bandwidth, and
recorded by coronagraphic interferometers equipped with active control of
wavefront phase and/or amplitude. In one method, a single deformable pupil
mirror is used to actively correct both diffraction and wavefront components of
the halo. This yields good diffraction suppression for complex pupil
obscuration, with high throughput over half the focal plane. In a second
method, the coronagraphic interferometer is used as a second stage after
conventional apodization. The halo from uncontrollable residual errors in the
pupil mask or wavefront is removed by destructive interference made directly at
the detector focal plane with an "anti-halo", synthesized by spatial light
modulators in the reference arm of the interferometer. In this way very deep
suppression may be achieved by control elements with greatly relaxed, and thus
achievable, tolerances. In both examples, systematic errors are minimized
because the planet imaging cameras themselves also provide the error sensing
data.Comment: Accepted by ApJ
Influence of feeding regimens on rat gut fluids and colonic metabolism of diclofenac-β-cyclodextrin
Feeding states may affect the performance of colonic prodrugs. The aim is to investigate the influence of feeding regimen in Wistar rats on: (i) distribution and pH contents along the gut and (ii) metabolism of two colonic prodrugs, diclofenac-β-cyclodextrin and a commercially available control, sulfasalazine, within the caecal and colonic contents. Male Wistar rats were subject to four different feeding regimens, the gut contents characterized (mass and pH) and the metabolism of prodrugs investigated.
The feeding regimen affects gut contents (mass and pH), more specifically in the stomach and lower intestine, and affects the rate of metabolism of diclofenac-β-cyclodextrin, but not that of sulfasalazine. The latter's degradation is much faster than that of diclofenac-β-cyclodextrin while the metabolism of both prodrugs is faster in colonic (versus caecal) contents. Fasting results in most rapid degradation of diclofenac-β-cyclodextrin, possibly due to lack of competition (absence of food) for microbial enzymatic activity
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