Biomedical subjects

S Chen

Publications and source records attributed to S Chen.

At least 19 recordsLinked to original sources

PubMed2007

Anaerobic biogasification of undiluted dairy manure in leaching bed reactors.

Dry anaerobic digestion of high solids animal manure is of increasing importance since conventional slurry digestion is not an effective system for these manures. The investment costs for large-size reactors, costs for heating these reactors, handling, dewatering, and the disposal of the digested residue decrease the benefits of conventional slurry anaerobic digestion for high solids animal manure. Even though leaching bed reactors (LBR) constitute a promising option for dry anaerobic biogasification of animal manure, no study is cited in the literature for animal manure, excluding a single study on cattle waste which utilized a similar concept in a different experimental set-up, namely a packed bed digester. Therefore, this work was undertaken to investigate the anaerobic biogasification of undiluted dairy manure in LBRs. To this purpose anaerobic leaching bed reactors (ALBR) packed with a mixture of dairy manure, anaerobic seed and wood powder/chips were operated. The ALBRs were fed with water, and the leachate that was collected from their effluents was subjected to biochemical methane potential (BMP) experiments to determine the biogas production. The results revealed that LBRs can successfully be applied to anaerobic digestion of undiluted dairy manure with around 25% improvement in biogas production relative to conventional (slurry) anaerobic digesters.

Anaerobiosis↗

PubMed2006

Characterization of strong promoters from an environmental Flavobacterium hibernum strain by using a green fluorescent protein-based reporter system.

We developed techniques for the genetic manipulation of Flavobacterium species and used it to characterize several promoters found in these bacteria. Our studies utilized Flavobacterium hibernum strain W22, an environmental strain we isolated from tree hole habitats of mosquito larvae. Plasmids from F. hibernum strain W22 were more efficiently (approximately 1,250-fold) transferred by electroporation into F. hibernum strain W22 than those isolated from Escherichia coli, thus indicating that an efficient restriction barrier exists between these species. The strong promoter, tac, functional in proteobacteria, did not function in Flavobacterium strains. Therefore, a promoter-trap plasmid, pSCH03, containing a promoterless gfpmut3 gene was constructed. A library of 9,000 clones containing chromosomal fragments of F. hibernum strain W22 in pSCH03 was screened for their ability to drive expression of the promoterless gfpmut3 gene. Twenty strong promoters were used for further study. The transcription start points were determined from seven promoter clones by the 5' rapid amplification of cDNA ends technique. Promoter consensus sequences from Flavobacterium were identified as TAnnTTTG and TTG, where n is any nucleotide, centered approximately 7 and 33 bp upstream of the transcription start site, respectively. A putative novel ribosome binding site consensus sequence is proposed as TAAAA by aligning the 20-bp regions upstream of the translational start site in 25 genes. Our primary results demonstrate that at least some promoter and ribosome binding site motifs of Flavobacterium strains are unusual within the bacterial domain and suggest an early evolutionary divergence of this bacterial group. The techniques presented here allow for more detailed genetics-based studies and analyses of Flavobacterium species in the environment.

Base Sequence↗

PubMed2006

Electron imaging with Medipix2 hybrid pixel detector.

The electron imaging performance of Medipix2 is described. Medipix2 is a hybrid pixel detector composed of two layers. It has a sensor layer and a layer of readout electronics, in which each 55 microm x 55 microm pixel has upper and lower energy discrimination and MHz rate counting. The sensor layer consists of a 300 microm slab of pixellated monolithic silicon and this is bonded to the readout chip. Experimental measurement of the detective quantum efficiency, DQE(0) at 120 keV shows that it can reach approximately 85% independent of electron exposure, since the detector has zero noise, and the DQE(Nyquist) can reach approximately 35% of that expected for a perfect detector (4/pi(2)). Experimental measurement of the modulation transfer function (MTF) at Nyquist resolution for 120 keV electrons using a 60 keV lower energy threshold, yields a value that is 50% of that expected for a perfect detector (2/pi). Finally, Monte Carlo simulations of electron tracks and energy deposited in adjacent pixels have been performed and used to calculate expected values for the MTF and DQE as a function of the threshold energy. The good agreement between theory and experiment allows suggestions for further improvements to be made with confidence. The present detector is already very useful for experiments that require a high DQE at very low doses.

Computer Simulation↗

PubMed2006

A facile HPLC method for optical purity and quantitative measurements of phenylalanine from the hydrolyzed aspartame under different pH and temperature after its derivatization with a fluorescent reagent.

In this paper, the artificial sweetener aspartame is deliberately hydrolyzed under different pH and temperature in the matrix, and time period for the hydrolysis. The HPLC analysis is then performed to quantitatively measure the amount and the optical purity of phenylalanine produced as a result of hydrolysis in the matrix after its functionalization with a fluorescent reagent. The results show that the amount of phenylalanine in the matrix is affected by the pH variation during the hydrolysis and found increased in low pH conditions. High temperature or long time periods for the decomposition also increases the amount, which indicates that beverages and foods containing aspartame as a sweetener may not be safe for phenylketonuria patients to consume if they are stored under these conditions. Conversely, the optical purity of phenylalanine, expressed as the percentage of D: -enantiomer, is not affected by pH variations. However, it decreases as the length of time elapsed is increased or surrounding temperature is elevated during the decomposition.

Aspartame↗

PubMed2006

A fluorescent electrophilic reagent, 9-fluorenone-4-carbonyl chloride (FCC), for the enantioresolution of amino acids on a teicoplanin phase under the elution of the methanol-based solvent mixture.

A fluorescent electrophilic reagent, 9-fluorenone-4-carbonyl chloride (FCC), is chosen to functionalize amino acids in alkaline medium before their HPLC resolution. FCC reacts with both primary and secondary amino acids to produce stable and highly fluorescent derivatives suitable for sensitive and efficient chromatographic determination and resolution on a teicoplanin chiral stationary phase (CSP) using the methanol-based solvent mixture as the mobile phase. The detection limit is in the picomole range and approximately 0.01% of the D: -enantiomer in an excess of the L: -enantiomer is detectable. However, the resolution is not reproducible under the elution of either the water- or the acetonitrile-based mobile phase. The increase in solubility of analyte in the mobile phase seems to be responsible. Upon comparison under the optimal chromatographic conditions, the resolution is better than that for the 9-fluorenylmethyl chloroformate (FMOC) or 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) derivatives reported previously.

Amino Acids↗

PubMed2006

Observation of relativistic cross-phase modulation in high-intensity laser-plasma interactions.

A nonlinear optical phenomenon, relativistic cross-phase modulation, is reported. A relativistically intense light beam (I = 1.3 x 10(18) W cm(-2), lambda = 1.05 microm) is experimentally observed to cause phase modulation of a lower intensity, copropagating light beam in a plasma. The latter beam is generated when the former undergoes the stimulated Raman forward scattering instability. The bandwidth of the Raman satellite is found to be broadened from 3.8-100 nm when the pump laser power is increased from 0.45-2.4 TW. A signature of relativistic cross-phase modulation, namely, asymmetric spectral broadening of the Raman signal, is observed at a pump power of 2.4 TW. The experimental cross-phase modulated spectra compared well with theoretical calculations. Applications to generation of high-power single-cycle pulses are also discussed.

Journal Article↗

PubMed2006

Constitutive nitric oxide acting as a possible intercellular signaling molecule in the initiation of radiation-induced DNA double strand breaks in non-irradiated bystander cells.

The initiation and propagation of the early processes of bystander signaling induced by low-dose alpha-particle irradiation are very important for understanding the underlying mechanism of the bystander process. Our previous investigation showed that the medium collected from cell culture exposed to low-dose alpha-particle rapidly induced phosphorylated form of H2AX protein foci formation among the non-irradiated medium receptor cells in a time-dependent manner. Using N(G)-methyl-L-arginine, 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate and N(omega)-nitro-L-arginine (L-NNA) treatment before exposure to 1 cGy alpha-particle, we showed in the present study that nitric oxide (NO(*)) produced in the irradiated cells was important and necessary for the DNA double strand break inducing activity (DIA) of conditioned medium and the generation of NO(*) in irradiated confluent AG1522 cells is in a time-dependent manner and that almost all NO(*) was generated within 15 min post-irradiation. Concurrently, the kinetics of NO(*) production in the medium of irradiated cells after irradiation was rapid and in a time-dependent manner as well, with a maximum yield observed at 10 min after irradiation with electron spin resonance analysis. Furthermore, our results that 7-Nitroindazole and L-NNA, but not aminoguanidine hemisulfate, treatment before exposure to 1 cGy alpha-particle significantly decrease the DIA of the conditioned medium suggested that constitutive NO(*) from the irradiated cells possibly acted as an intercellular signaling molecule to initiate and activate the early process (<or=30 min) of bystander response after low-dose irradiation.

Alpha Particles↗

PubMed2006

Measurement of the N-->Delta(+)(1232) transition at high-momentum transfer by pi(0) electroproduction.

We report a new measurement of the exclusive electroproduction reaction gamma(*)p-->pi(0)p to explore the evolution from soft nonperturbative physics to hard processes via the Q(2) dependence of the magnetic (M(1+)), electric (E(1+)), and scalar (S(1+)) multipoles in the N-->Delta transition. 9000 differential cross section data points cover W from threshold to 1.4 GeV/c(2), 4pi center-of-mass solid angle, and Q(2) from 3 to 6 GeV(2)/c(2), the highest yet achieved. It is found that the magnetic form factor G(M)(*) decreases with Q(2) more steeply than the proton magnetic form factor, the ratio E(1+)/M(1+) is small and negative, indicating strong helicity nonconservation, and the ratio S(1+)/M(1+) is negative, while its magnitude increases with Q(2).

Journal Article↗

PubMed2006

Search for Theta++ pentaquarks in the exclusive reaction gammap-->K+K-p.

The reaction gammap --> pK+K- was studied at Jefferson Lab with photon energies from 1.8 to 3.8 GeV using a tagged photon beam. The goal was to search for a Theta++ pentaquark, a narrow, doubly charged baryon state having strangeness S=+1 and isospin I=1, in the pK+ invariant mass spectrum. No statistically significant evidence of a Theta++ was found. Upper limits on the total and differential cross section for the reaction gammap --> K-Theta++ were obtained in the mass range from 1.5 to 2.0 GeV/c2, with an upper limit for a narrow resonance with a mass M(Theta++) = 1.54 GeV/c2 of about 0.15 nb, 95% C.L.. This result places a stringent upper limit on the Theta++ width Gamma(Theta++) <0.1 MeV/c2.

Journal Article↗

PubMed2006

Phase locking and in-phase supermode selection in monolithic multicore fiber lasers.

We report a compact multicore fiber laser that utilizes an all-fiber approach for phase locking and in-phase supermode selection. By splicing passive coreless fibers of controlled lengths to both ends of an active 19-core fiber, we demonstrate that the fundamental in-phase supermode can be selectively excited with a completely monolithic fiber device, instead of conventional free-space and bulk optics, to achieve phase-locked operation for a multiemitter laser device.

Journal Article↗

PubMed2006

Measurement of deeply virtual compton scattering with a polarized-proton target.

The longitudinal target-spin asymmetry AUL for the exclusive electroproduction of high-energy photons was measured for the first time in ep-->e;'pgamma. The data have been accumulated at JLab with the CLAS spectrometer using 5.7 GeV electrons and a longitudinally polarized NH3 target. A significant azimuthal angular dependence was observed, resulting from the interference of the deeply virtual Compton scattering and Bethe-Heitler processes. The amplitude of the sinvarphi moment is 0.252+/-0.042stat+/-0.020sys. Theoretical calculations are in good agreement with the magnitude and the kinematic dependence of the target-spin asymmetry, which is sensitive to the generalized parton distributions H and H.

Journal Article↗

PubMed2006

Kink formation and motion in carbon nanotubes at high temperatures.

We report that kink motion is a universal plastic deformation mode in all carbon nanotubes when being tensile loaded at high temperatures. The kink motion, observed inside a high-resolution transmission electron microscope, is reminiscent of dislocation motion in crystalline materials: namely, it dissociates and multiplies. The kinks are nucleated from vacancy creation and aggregation, and propagate in either a longitudinal or a spiral path along the nanotube walls. The kink motion is related to dislocation glide and climb influenced by external stress and high temperatures in carbon nanotubes.

Journal Article↗

PubMed2006

Surgical interventions for bilateral congenital cataract.

BACKGROUND: Congenital cataracts are opacities of the lens in one or both eyes of children that cause a reduction in vision severe enough to require surgery. Cataract is the largest treatable cause of visual loss in childhood. Paediatric cataracts provide different challenges to those in adults. Intense inflammation, amblyopia and posterior capsule opacification can affect results of treatment. Two treatments commonly considered for congenital cataract are lensectomy and lens aspiration. OBJECTIVES: The objective of this review was to assess the effects of surgical treatments for bilateral symmetrical congenital cataracts. Success was measured according to the vision attained and occurrence of adverse events. SEARCH STRATEGY: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library, which contains the Cochrane Eyes and Vision Group Trials Register (2005, Issue 2), MEDLINE (1966 to June 2005), EMBASE (1980 to June 2005, week 27), LILACS (6 July 2005), the Science Citation Index and the reference list of the included studies. We also contacted trial investigators and experts in the field for details of further studies. SELECTION CRITERIA: We included all prospective, randomised controlled trials that compared one type of cataract surgery to another, or to no surgery, in children with bilateral congenital cataracts aged 15 years or younger. DATA COLLECTION AND ANALYSIS: Two authors extracted data. No meta-analysis was performed. MAIN RESULTS: Four trials met the inclusion criteria. All trials were concerned with reducing the development of visual axis opacification (VAO). This was achieved with techniques that included an anterior vitrectomy or optic capture. Posterior capsulotomy alone was inadequate except in older children. AUTHORS' CONCLUSIONS: Evidence exists for the care of children with congenital or developmental bilateral cataracts to reduce the occurrence of visual axis opacification. Further randomised trials are required to inform modern practice about other concerns including the timing of surgery, age for implantation of an intraocular lens and development of long-term complications such as glaucoma and retinal detachment.

Cataract↗

PubMed2006

Search for the Theta+ Pentaquark in the gammad--> DeltanK+ reaction measured with the CLAS spectrometer.

For the first time, the reaction gammad-->DeltanK+ has been analyzed in order to search for the exotic pentaquark baryon Theta+(1540). The data were taken at Jefferson Laboratory, using the Hall-B tagged-photon beam of energy between 0.8 and 3.6 GeV and the CEBAF Large Acceptance Spectrometer (CLAS). No statistically significant structures were observed in the nK+ invariant-mass distribution. The upper limit on the gammad-->DeltaTheta+ integrated cross section has been calculated and found to be between 5 and 25 nb, depending on the production model assumed. The upper limit on the differential cross section is also reported.

Journal Article↗

PubMed2006

Characterization of a method for profiling gene expression in cells recovered from intact human prostate tissue using RNA linear amplification.

Coupling array technology to laser capture microdissection (LCM) has the potential to yield gene expression profiles of specific cell populations within tissue. However, remaining problems with linear amplification preclude accurate expression profiling when using the low nanogram amounts of RNA recovered after LCM of human tissue. We describe a novel robust method to reliably amplify RNA after LCM, allowing direct probing of 12K gene arrays. The fidelity of amplification was demonstrated by comparing the ability of amplified RNA (aRNA) versus that of native RNA to identify differentially expressed genes between two different cell lines, demonstrating a 99.3% concordance between observations. Array findings were validated by quantitative polymerase chain reaction analysis of a randomly selected subset of 32 genes. Using LCM to recover normal (N=5 subjects) or cancer (N=3) cell populations from intact human prostate tissue, three differentially expressed genes were identified. Independent investigators have previously identified differential expression of two of these three genes, hepsin and beta-microseminoprotein, in prostate cancer. Taken together, the current study demonstrates that accurate gene expression profiling can readily be performed on specific cell populations present within complex tissue. It also demonstrates that this approach efficiently identifies biologically relevant genes.

Cell Line, Tumor↗

PubMed2006

Search for the Theta+ pentaquark in the reaction gammad --> pK-K+n.

A search for the Theta+ in the reaction gammad --> pK-K+n was completed using the CLAS detector at Jefferson Lab. A study of the same reaction, published earlier, reported the observation of a narrow Theta+ resonance. The present experiment, with more than 30 times the integrated luminosity of our earlier measurement, does not show any evidence for a narrow pentaquark resonance. The angle-integrated upper limit on Theta+ production in the mass range of 1.52-1.56 GeV/c2 for the gammad --> pK-Theta+ reaction is 0.3 nb (95% C.L.). This upper limit depends on assumptions made for the mass and angular distribution of Theta+ production. Using Lambda(1520) production as an empirical measure of rescattering in the deuteron, the cross section upper limit for the elementary gamman --> K-Theta+ reaction is estimated to be a factor of 10 higher, i.e., approximately 3 nb (95% C.L.).

Journal Article↗

PubMed2006

MAPKAPK2 and HSP27 are downstream effectors of p38 MAP kinase-mediated matrix metalloproteinase type 2 activation and cell invasion in human prostate cancer.

Although cell invasion is a necessary early step in cancer metastasis, its regulation is not well understood. We have previously shown, in human prostate cancer, that transforming growth factor beta (TGFbeta)-mediated increases in cell invasion are dependent upon activation of the serine/threonine kinase, p38 MAP kinase. In the current study, downstream effectors of p38 MAP kinase were sought by first screening for proteins phosphorylated after TGFbeta treatment, only in the absence of chemical inhibitors of p38 MAP kinase. This led us to investigate mitogen-activated protein kinase-activated protein kinase 2 (MAPKAPK2), a known substrate of p38 MAP kinase, as well as heat-shock protein 27 (HSP27), a known substrate of MAPKAPK2, in both PC3 and PC3-M human prostate cells. After transient transfection, wild-type MAPKAPK2 and HSP27 both increased TGFbeta-mediated matrix metalloproteinase type 2 (MMP-2) activity, as well as cell invasion, which in turn was inhibited by SB203580, an inhibitor of p38 MAP kinase. Conversely, dominant-negative MAPKAPK2 blocked phosphorylation of HSP27, whereas dominant-negative MAPKAPK2 or mutant, non-phosphorylateable, HSP27 each blocked TGFbeta-mediated increases in MMP-2, as well as cell invasion. Similarly, knock down of MAPKAPK2, HSP27 or both together, by siRNA, also blocked TGFbeta-mediated cell invasion. This study demonstrates that both MAPKAPK2 and HSP27 are necessary for TGFbeta-mediated increases in MMP-2 and cell invasion in human prostate cancer.

Adenocarcinoma↗

PubMed2006

Prediction of human absorption of natural compounds by the non-everted rat intestinal sac model.

A major concern in natural drug research is that many substances with potent biological activity in vitro are unable to generate good activity in vivo owing to their poor water-solubility, poor permeability and/or poor stability. The permeability of drug candidates across the intestinal mucosa is one of the most important factors in defining drug bioavailability and biological activity. In order to screen promising compounds for further investigation, a non-everted rat intestinal sac model has been developed successfully to assay the permeability of natural compounds and to predict their human absorption. In this system, the drug solution was placed in non-everted intestinal sacs (NEIS), which were placed in an acceptor solution and the permeability of drug across intestine walls was determined. The feasibility of this method has been validated and demonstrated for 11 model compounds chosen from currently marketed drugs whose human fraction absorbed (Fa) data have been reported. The results of the studies indicate that a good relationship exists between the permeability of the model drugs and their corresponding Fa data. The permeability of 13 natural compounds was evaluated using this system. Only fraxinellone and vitexin-7-glucoside exhibited high intestinal permeability, and predictive of excellent human absorption, which awaits confirmation from further investigation in vivo. This model provides an alternative method to everted intestinal sacs for the evaluation of in vitro permeability in rats, and for estimating human absorption of drugs. It may therefore hold great promise for oral absorption screening of new drug candidates.

Animals↗