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Biomedical subjects

J Zhang

Publications and source records attributed to J Zhang.

At least 253 records · Page 14Linked to original sources
PubMed2002

Prediction of food thermal process evaluation parameters using neural networks.

Two neural networks (ANN) were developed to predict thermal process evaluation parameters g and f(h)/U (the ratio of heating rate index to the sterilizing value), respectively. The temperature change required for the thermal destruction curve to traverse one log cycle (z), cooling lag factor (j(c)) andf(h)/U were input variables for predicting g and z, while j(c) and g were inputs for predicting f(h)/U. The data used to train and verify the ANN were obtained from reported values. Shrinking of input and output variables using natural logarithm function improved the prediction accuracy. The use of "Wardnets" with three slabs of 14 nodes in each slab, with a learning rate of 0.7 and momentum of 0.9 provided the best predictions. The g (unshrunk values) was predicted with a mean relative error of 1.25 +/- 1.77%, and a mean absolute error of 0.11 +/- 0.16 degrees F. The f(h)/U was predicted with a mean relative error of 1.41 +/- 3.40%, and a mean absolute error of 2.43 +/- 15.97, using 10 nodes in each slab. The process time calculated using the g from the ANN models closely followed the time calculated from the tabulated gvalues (RMS=0.612 min, average absolute error=0.466 min with an S.D. of 0.400 min).

Algorithms↗
PubMed2002

Tissue factor deficiency causes cardiac fibrosis and left ventricular dysfunction.

Exposure of blood to tissue factor (TF) activates the extrinsic (TF:FVIIa) and intrinsic (FVIIIa:FIXa) pathways of coagulation. In this study, we found that mice expressing low levels of human TF ( approximately 1% of wild-type levels) in an mTF(-/-) background had significantly shorter lifespans than wild-type mice, in part, because of spontaneous fatal hemorrhages. All low-TF mice exhibited a selective heart defect that consisted of hemosiderin deposition and fibrosis. Direct intracardiac measurement demonstrated a 30% reduction (P < 0.001) in left ventricular function in 8-month-old low-TF mice compared with age-matched wild-type mice. Mice expressing low levels of murine FVII ( approximately 1% of wild-type levels) exhibited a similar pattern of hemosiderin deposition and fibrosis in their hearts. In contrast, FIX(-/-) mice, a model of hemophilia B, had normal hearts. Cardiac fibrosis in low-TF and low-FVII mice appears to be caused by hemorrhage from cardiac vessels due to impaired hemostasis. We propose that TF expression by cardiac myocytes provides a secondary hemostatic barrier to protect the heart from hemorrhage.

Animals↗
PubMed2002

Effects of delay time on transient Ni-like x-ray lasers.

In transient collisional excitation scheme, a long (nanosecond) prepulse is used to perform and ionize plasmas. After a delay time, a short (sub- or picosecond) intense laser pulse is used to rapidly heat the plasma. This results in transient x-ray lasers with high gain. Effects of delay time on transient collisional excitation nickel-like x-ray lasers are investigated analytically using a simple model. The calculations show that the longer delay time can greatly relax the density gradient. This is very critical for the propagation of x-ray lasers. However, a too long delay will reduce the electron temperature of the plasma before the arrival of the short pulse. Increasing the intensity of the long pulse or extending the pulse duration can keep the temperature required to maintain a high percentage of Ni-like ions while the delay time is longer. Similarly, increasing the intensity of the short pulse or extending the duration can also raise the electron temperature, resulting in higher gain coefficient. Our results indicate that extending the pulse duration is more efficient than that of increasing the intensity.

Journal Article↗
PubMed2002

Use of frozen bagged seed inoculum for secondary metabolite and bioconversion processes at the pilot scale.

Frozen bagged seed inoculum was prepared, thawed and tested for seven cultures. Thawing techniques were developed and other key influences on thawing rate were quantified; seed bag thawing without a water bath rarely required more than 4 to 5 h and was as short as 0.5 to 1 h for lower fill volume bags. Testing included growth of bagged seed as a function of bag fill volume (0.5, 1.0, 2.0, and 3.5 L), comparison of culture age at time of bagging, growth of bagged versus laboratory-prepared seed, productivity of production cultures derived from bagged versus laboratory-prepared seed, growth of bagged seed as a function of volume percent glycerol added at time of bagging, and growth of bagged seed as a function of frozen storage time and temperature. For each culture tested, conditions were developed such that seed tanks inoculated with bagged seed showed only minimal delay in attaining the target oxygen uptake rate (OUR) relative to seed tanks inoculated with laboratory-prepared inoculum. Although the bag fill volume did influence culture growth in some cases, bag fill volumes required were reasonable (typically 2.0 to 3.5 L) compared with laboratory seed inoculum volumes of 2.0 L. In the most remarkable example, frozen bagged seed was prepared from a second-stage seed-tank cultivation of Glarca lozoyensis, then thawed and inoculated into first-stage seed medium. It grew to the desired OUR in a similar timeframe as laboratory-prepared inoculum inoculated into first-stage seed medium. Thus, the frozen bagged seed replaced an existing laboratory inoculum preparation period of 7 days without an appreciable delay in either of the two subsequent seed-tank growth stages. Furthermore, productivities were found to be comparable for bagged-seed-derived and laboratory-seed-derived production cultivations for four different fermentation processes.

Bioreactors↗
PubMed2002

Antibody/antigen affinity behavior in liquid environment with electrical impedance analysis of quartz crystal microbalances.

Electrical impedance analysis has been used to study anti-human immunoglobulin G (anti-h IgG) adsorption and the subsequent human immunoglobulin G (hIgG) or rabbit immunoglobulin G (rIgG) affinity reaction in aqueous liquids on a polystyrene (PS)-modified quartz crystal microbalance (QCM) surface. Time-dependent adsorption data of both the frequency shift and the electrical equivalent parameters (motional resistance, shunt capacitance, quality factor, etc) are monitored. It was found that the motional resistance, R, increases while the resonance frequency, f, decreases during both the anti-h IgG immobilization and the subsequent affinity process. Decreasing f primarily arises from the increased mass loading. Increasing R indicates more power dissipation (increased losses) in the system. The change in motional resistance, delta R, in the affinity reaction is considerably larger than that in anti-h IgG immobilization adsorption process, although the resonant frequency shifts, delta f, are very close in these two processes. Specifically, for a saturated solution, the ratio of delta R/delta f is 9.45 x 10 (-3) Omega/Hz for anti-h IgG adsorption and 28.1 x 10 (-3) omega/Hz for anti-h IgG/hIgG binding respectively, indicating the increased power dissipation with the increasing binding molecules. The shunt capacitance changes little in the hIgG binding process ( approximately 0.01 pF).

Animals↗
PubMed2002

Emission of a hot electron jet from intense femtosecond-laser-cluster interactions.

A directional hot electron jet with energy higher than 100 keV was generated along the laser propagation direction from Ar clusters irradiated with a laser pulse of duration 28 fs and intensity 1 x 10(17) W/cm(2). The hot electron jet was detected only with linearly polarized laser pulses, not with circularly polarized pulses. Channel betatron resonance is believed to be the main accelerating mechanism for this directional hot electron jet.

Journal Article↗
PubMed2002

Zener tunneling between landau orbits in a high-mobility two-dimensional electron gas.

Magnetotransport in a laterally confined two-dimensional electron gas (2DEG) can exhibit modified scattering channels owing to a tilted Hall potential. Transitions of electrons between Landau levels with shifted guiding centers can be accomplished through a Zener tunneling mechanism, and make a significant contribution to the magnetoresistance. A remarkable oscillation effect in weak field magnetoresistance has been observed in high-mobility 2DEGs in GaAs -Al Ga 0.3As (0.7) heterostructures, and can be well explained by the Zener mechanism.

Journal Article↗
PubMed2002

KCl cotransport regulation and protein kinase G in cultured vascular smooth muscle cells.

K-Cl cotransport is activated by vasodilators in erythrocytes and vascular smooth muscle cells and its regulation involves putative kinase/phosphatase cascades. N-ethylmaleimide (NEM) activates the system presumably by inhibiting a protein kinase. Nitrovasodilators relax smooth muscle via cGMP-dependent activation of protein kinase G (PKG), a regulator of membrane channels and transporters. We investigated whether PKG regulates K-Cl cotransport activity or mRNA expression in normal, PKG-deficient-vector-only-transfected (PKG-) and PKG-catalytic-domain-transfected (PKG+) rat aortic smooth muscle cells. K-Cl cotransport was calculated as the Cl-dependent Rb influx, and mRNA was determined by semiquantitative RT-PCR. Baseline K-Cl cotransport was higher in PKG+ than in PKG- cells (p <0.01). At 0.5 mM, NEM stimulated K-Cl cotransport by 5-fold in PKG- but not in PKG+ cells. However, NEM was more potent although less effective to activate K-Cl cotransport in normal (passage 1-3) and PKG+ than in PKG- cells. In PKG- cells, [(dihydroindenyl) oxy] alkanoic acid (300 mM) but not furosemide (1 mM) inhibited K-Cl cotransport. Furthermore, no difference in K-Cl cotransport mRNA expression was observed between these cells. In conclusion, this study shows that manipulation of PKG expression in vascular smooth muscle cells affects K-Cl cotransport activity and its activation by NEM.

Acetates↗
PubMed2002

Characterization of a bioflocculant produced by the marine myxobacterium Nannocystis sp. NU-2.

The marine myxobacterium strain NU-2, which can grow on high concentrations (up to 7%) of NaCl, was isolated from a salt soil sample collected from the coast of the Huanghai Sea, China. Morphological properties and 16S rDNA sequence analysis indicated that the isolate is a novel species related to the genus Nannocystis. Nannocystis sp. NU-2 produced a new kind of flocculating substance in a starch medium with a yield of 14.8 g l(-1). The NU-2 flocculant was composed of 40.3% proteins and 56.5% polysaccharides, of which glucose, mannose and glucuronic acid were the principal constituents in the relative proportions of 5:4:1. The flocculation activity of the NU-2 flocculant depends strongly on cations such as Fe(3+) and Al(3+). When a 30 mg l(-1) FeCl(3) solution is present in kaolin clay suspension, 30 mg l(-1)of the flocculant produced a high flocculating activity value of 90%, which remained unchanged over an extensive pH range (pH 2.0-13.0). The flocculant was tested for its ability to bleach dyeing liquors, and the bleaching activities were 98.2% for acid red in 100 mg l(-1)of the flocculant and 99.0% for direct emerald blue in 50 mg l(-1)of the flocculant under test conditions. Use of the flocculant to bleach basic pink and cation emerald blue liquors was not effective.

Bacterial Proteins↗
PubMed2002

A locust DNA-binding protein involved in gene regulation by juvenile hormone.

Although juvenile hormone (JH) has essential roles in insect development and reproduction, the molecular mechanisms of gene regulation by JH remain an enigma. In Locusta migratoria, the partially palindromic 15-nt sequence, GAGGTTCGAG(A)/(T)CCT(T)/(C), found upstream of a JH-induced gene, jhp21, was designated as a putative juvenile hormone response element (JHRE). When JH-deprived adult female locusts were treated with the active JH analog, methoprene, a fat body nuclear factor that bound specifically to JHRE appeared after 24 h. Binding exhibited a preference for an inverted repeat with GAGGTTC in the left half-site, a single nucleotide spacer, and a right half-site in which some variation is acceptable. Binding to JHRE was abolished by phosphorylation catalyzed by a C-type protein kinase present in the nuclear extracts. The DNA-binding protein is thus believed to be a transcription factor, which is brought to an active state through the action of JH and then participates in the regulation of certain JH-dependent genes.

Animals↗
PubMed2002

Synthesis of sub-micromolar inhibitors of MraY by exploring the region originally occupied by the diazepanone ring in the liposidomycin structure.

The synthesis and inhibitory activity against MraY of a series of simplified analogues of liposidomycins are described. These compounds were mainly obtained by performing parallel synthesis in the 6'-position of a scaffold that gathers key features found necessary for the binding to MraY. Thus, inhibitory activity was improved from 5300 to 140 nM. This improvement was correlated with the length and lipophilicity of substituents, but was found to be independent of the nature of the chemical bond generated. In addition, some of these inhibitors presented encouraging antibacterial activities.

Aminoglycosides↗
PubMed2002

Bilirubin produces apoptosis in cultured bovine brain endothelial cells.

Blood components such as oxyhemoglobin are believed to cause cerebral vasospasm by inducing contraction and cell death in cerebral arteries. We have observed previously that oxyhemoglobin produces apoptotic changes in cultured endothelial cells. This study was undertaken to explore if bilirubin, a bi-product of hemoglobin degradation, will produce similar cytotoxicity in endothelial cells. Cultured bovine brain microvascular endothelial cells were incubated in four concentrations of bilirubin (10, 25, 50, and 100 microM) for varying times (6, 12, and 24 h). Control cells were incubated in saline or vehicle (NaOH solution, <0.01% of 0.01 N) for similar time periods. The cultured cells were then observed microscopically for evidence of cellular alterations. Bilirubin (10-100 microM) produced apoptosis that appeared time-dependent but not clearly concentration-dependent. Biochemical markers for apoptosis such as DNA fragmentation and PARP cleavage were induced by bilirubin. We conclude that endothelial cells may undergo apoptosis after exposure to bilirubin.

Animals↗
PubMed2002

The paradoxical effect of acetaminophen on CYP3A4 activity and content in transfected HepG2 cells.

HepG2 cell lines that constitutively and stably express human CYP3A4 were constructed in order to study enzyme interactions with CYP3A4 as the only P450 present. CYP3A4 activity and content were assessed by the metabolism of fentanyl, a CYP3A substrate, and Western blots. Northern blots were used to examine the effects of acetaminophen (APAP) on CYP3A4-mRNA. The HepG2 cell lines' CYP3A4 activity was stable over time. High concentrations of APAP inhibited CYP3A4 activity. At lower concentrations, APAP produced a dose-dependent increase in CYP3A4 activity and content. No increases in CYP3A4-mRNA were seen. Incubation with cycloheximide caused a decrease in fentanyl metabolism secondary to a decrease in P450 levels that was prevented by the coincubation with APAP. Additionally, human microsomal CYP3A4 was stabilized by APAP against cytosol-mediated degradation. In our models, APAP appears to increase CYP3A4 activity. This increase appears to be via substrate stabilization. This is the first report that APAP can increase CYP3A4 activity and content in transfected HepG2 cells.

Acetaminophen↗
PubMed2002

Stochastic heating and acceleration of electrons in colliding laser fields in plasma.

We propose a mechanism that leads to efficient acceleration of electrons in plasma by two counterpropagating laser pulses. It is triggered by stochastic motion of electrons when the laser fields exceed some threshold amplitudes, as found in single-electron dynamics. It is further confirmed in particle-in-cell simulations. In vacuum or tenuous plasma, electron acceleration in the case with two colliding laser pulses can be much more efficient than with one laser pulse only. In plasma at moderate densities, such as a few percent of the critical density, the amplitude of the Raman-backscattered wave is high enough to serve as the second counterpropagating pulse to trigger the electron stochastic motion. As a result, even with one intense laser pulse only, electrons can be heated up to a temperature much higher than the corresponding laser ponderomotive potential.

Journal Article↗
PubMed2002

Soluble osteopontin inhibits apoptosis of adherent endothelial cells deprived of growth factors.

Osteopontin (OPN) is primarily an extracellular glycosylated phosphoprotein capable of stimulating cell migration and cell attachment, predominantly to mineralized surfaces. Found in moderate levels in plasma, it acts as a cytokine able to modify gene expression via integrins and certain CD44 isoforms. In this work we show that soluble OPN inhibits apoptosis of adherent human umbilical vein endothelial cells incubated in medium lacking critical growth factors and cytokines. In a dose-dependent manner OPN reduced the formation of apoptotic bodies and suppressed DNA fragmentation. OPN also caused an increase in Bcl-X(L) mRNA levels, suppressed the apparent dispersion of Bcl-X(L) throughout the cytoplasm, and slightly enhanced IkappaB-alpha protein degradation. These data suggest that a function of OPN in homeostatic processes is to facilitate the survival of stressed endothelial cells, possibly by occupying unligated integrins and suppressing integrin-mediated death.

Animals↗
PubMed2002

Protein kinase C regulates [3H]D-aspartate release in auditory brain stem nuclei.

We previously found that unilateral cochlear ablation altered transmitter release from glutamatergic synaptic endings in several brain stem auditory nuclei. To determine if this release activity could be regulated by protein kinase C (PKC), which has been associated with regulation of transmitter release, the electrically evoked release of [3H]d-aspartate ([3H]d-Asp) was quantified in vitro as an index of exocytosis from glutamatergic presynaptic endings in the major subdivisions of the cochlear nucleus (CN) and in the main nuclei of the superior olivary complex (SOC). Treating dissected tissues with a PKC activator, such as phorbol 12,13-diacetate (PDA) or phorbol 12,13-dibutyrate (PDBu) (3 microM), elevated the evoked release of [3H]d-Asp by 1.5- to 3.3-fold. The PKC inhibitor Ro31-8220 (50 nM) did not alter the evoked release but blocked the stimulatory effects of PDA and PDBu. These findings suggested that PKC could positively regulate transmitter release from glutamatergic presynaptic endings in brain stem auditory pathways. Seven days after unilateral cochlear ablation, when cochlear nerve endings had degenerated in the ipsilateral CN, PDBu elevated the evoked release bilaterally in each CN subdivision and SOC nucleus, implying that PKC could regulate glutamatergic release in the noncochlear pathways remaining in the ipsilateral CN and in the other pathways after unilateral hearing loss. After 145 postlesion days, Ro31-8220 blocked endogenous elevations in the evoked release in the ipsilateral SOC but did not alter the elevated or upregulated release in the other tissues. This suggested that the elevations of glutamatergic release activity in the ipsilateral SOC that appeared after unilateral cochlear ablation depended on endogenous activation of PKC.

Animals↗
PubMed2002

Metabolic alterations in cerebrospinal fluid from double hemorrhage model of dogs.

OBJECTIVE: Even though cerebral vasospasm after subarachnoid hemorrhage (SAH) causes cerebral ischemia or infarction, the metabolic alterations in cerebrospinal fluids (CSF) after SAH have not been studied. This study was undertaken to measure the levels of glucose, lactate, pyruvate and glutamate in CSF from double hemorrhage dog models. METHOD: Thirty-two mongrel dogs of either sex, weighing 15-30 kg, underwent double hemorrhage by percutaneous needle puncture of the cisterna magna and injection of autologous blood on day 0 and day 2. The dogs were then sacrificed on day 3, 5 and 7, after collecting CSF. In another study, the dogs were treated with mitogen-activated protein kinase (MAPK) inhibitors PD98059 and U0126, and caspase-2 and caspase-3 inhibitors from day 3 to day 6 after initial blood injection. CSF was collected on day 7 before dogs were sacrificed. The concentration of glucose, lactate, pyruvate and glutamate in CSF was measured by photometrical method. RESULTS: Compared with CSF collected on day 0, glucose was decreased on days 5-7, lactate was increased on days 2-7, pyruvate was increased on days 2-7, and glutamate was increased on days 3-7 (P < 0.05). In the groups treated with MAPK or caspase inhibitors, most of the metabolic alterations remained unchanged as compared with CSF from untreated dogs. Clinically, caspase inhibitors-2 and -3, and MAPK inhibitor U0126 all failed to prevent vasospasm. MAPK inhibitor PD98059 partially prevented vasospasm. CONCLUSION: Our data demonstrated a metabolic alteration of glucose, glutamate, lactate and pyruvate in CSF during cerebral vasospasm. This metabolic change is consistent with the time course of cerebral vasospasm. This study suggests that brain energy metabolites and excitative amino acids are altered during cerebral vasospasm.

Analysis of Variance↗