DNA microarray analysis of gene expression in endothelial cells in response to 24-h shear stress

The recently developed DNA microarray technology provides a powerful and efficient tool to rapidly compare the differential expression of a large number of genes. Using the DNA microarray approach, we investigated gene expression profiles in cultured human aortic endothelial cells (HAECs) in response to 24 h of laminar shear stress at 12 dyn/cm(2). This relatively long-term shearing of cultured HAECs led to the modulation of the expression of a number of genes. Several genes related to inflammation and EC proliferation were downregulated, suggesting that 24-h shearing may keep ECs in a relatively noninflammatory and nonproliferative state compared with static cells. Some genes were significantly upregulated by the 24-h shear stress; these includes genes involved in EC survival and angiogenesis (Tie2 and Flk-1) and vascular remodeling (matrix metalloproteinase 1). These results provide information on the profile of gene expression in shear-adapted ECs, which is the case for the native ECs in the straight part of the aorta in vivo.

Determinants of hepato- and spleno-megaly in Hunan, China: cross-sectional survey data from areas endemic for schistosomiasis

In order to understand the determinants of schistosome-related hepato- and spleno-megaly better, 14,002 subjects aged 3-60 years (59% male; mean age = 32 years) were randomly selected from 43 villages, all in Hunan province, China, where schistosomiasis caused by Schistosoma japonicum is endemic. The abdomen of each subject was examined along the mid-sternal (MSL) and mid-clavicular lines, for evidence of current hepato- and/or spleno-megaly, and a questionnaire was used to collect information on the medical history of each individual. Current infections with S. japonicum were detected by stool examination. Almost all (99.8%) of the subjects were ethnically Han by descent and most (77%) were engaged in farming. Although schistosomiasis appeared common (42% of the subjects claiming to have had the disease), only 45% of the subjects said they had received anti-schistosomiasis drugs. Overall, 1982 (14%) of the subjects had S. japonicum infections (as revealed by miracidium-hatching tests and/or Kato-Katz smears) when examined and 22% had palpable hepatomegaly (i.e. enlargement of at least 3 cm along the MSL), although only 2.5% had any form of detectable splenomegaly (i.e. a Hackett's grade of at least 1). Multiple logistic regression revealed that male subjects, fishermen, farmers, subjects aged > or = 25 years, subjects with a history of schistosomiasis, and subjects who had had bloody stools in the previous 2 weeks were all at relatively high risk of hepato- and/or spleno-megaly. In areas moderately endemic for Schistosoma japonicum, occupational exposure and disease history appear to be good predictors of current disease status among older residents. These results reconfirm those reported earlier in the same region.

Efficacy of praziquantel against Schistosoma japonicum: field evaluation in an area with repeated chemotherapy compared with a newly identified endemic focus in Hunan, China

This study conducted in 1999/2000 was designed to evaluate the efficacy of praziquantel against Schistosoma japonicum in an area with repeated chemotherapy (Area A) compared with a newly identified endemic focus (Area B) in Hunan Province, China. The population size was 2015 and 2180 in Areas A and B, respectively, of which 1129 and 1298 subjects received stool examination. A total of 230 subjects were identified by the Kato-Katz technique (4 smears per person) as being infected with S. japonicum, 124 in Area A (prevalence 11%) and 106 in Area B (prevalence 8.2%). They were treated with a single oral dose of praziquantel (40 mg/kg) in the non-transmission season. A follow-up stool examination was made 50 days after treatment. Among the 220 cases followed, 22 were found stool-egg-positive, with an overall cure rate of 90%, and 99% reduction of infection intensity (eggs per gram stool). No significant difference was found in cure rates between the 2 areas (89.7% vs 90.3%). The efficacy of the drug in the area with repeated chemotherapy was not significantly different from that in the newly identified endemic focus. This study, therefore, suggests that the efficacy of praziquantel against S. japonicum has not changed in the Dongting Lake region after more than 14 years of mass chemotherapy, and there is no evidence of tolerance or resistance of S. japonicum against praziquantel.

Effects of morphological patterning on endothelial cell migration

The migration of vascular endothelial cells (ECs) plays an important role in vascular remodeling. Here we studied the effects of cell morphology on the migration of bovine aortic ECs by culturing cells on micropatterned strips of collagen matrix (60-, 30-, and 15-microm wide). The spreading areas of the cells on 15- and 30-microm wide strips were 30% lower than those on 60-microm wide strips and unpatterned collagen. The cells on 15-microm wide strips completely aligned in the direction of the strip, and had significantly lower shape index than those in all other groups. On strips of all widths, ECs tended to migrate in the direction of strips. ECs on 15-microm wide strips had highest speed, particularly in the direction of the strip. Vinculin staining showed that the leading edge of ECs on 15-microm wide strips had focal adhesions that were oriented with their lamellipodial protrusion and the direction of cell migration; this arrangement of the focal adhesions may promote EC migration. The present study provides direct evidence on the role of cell morphology in EC migration, and will help us to understand the mechanisms of EC migration during angiogenesis and wound healing.

Effects of flow patterns on endothelial cell migration into a zone of mechanical denudation

Vascular endothelial cells (ECs) in vivo are subject to different flow conditions due to the variation in vessel geometry. The aim of this study is to elucidate the effects of different flow conditions on EC monolayer migration into a mechanically denuded zone and their underlying mechanisms. Both laminar and disturbed flows significantly enhanced EC migration. EC migration speed was the fastest under laminar flow, which preferentially promoted directional EC migration from the upstream side of the wounded monolayer. C3 exoenzyme (a Rho inhibitor) inhibited EC migration under static and flow conditions, and markedly reduced the effects of flow on EC migration. These results indicate that flow promotes EC migration through the Rho signaling pathway. Genistein (a tyrosine kinase inhibitor) selectively retarded EC migration under disturbed flow, suggesting that tyrosine phosphorylation may play a role in EC migration under disturbed flow. This study has demonstrated that different flow patterns differentially affect EC monolayer migration into the denuded zone involving multiple mechanisms.

[Clinical study on effect of hewei capsule on promoting gastric dynamics]

OBJECTIVE

To investigate the effect of Hewei capsule (HWC) on gastric dynamics.

METHODS

Sixty-two patients with dysmotility-like functional dyspepsia (DFD) were included in the study. The principal symptoms, electrogastrogram (EGG), plasma motilin (MTL), serum gastrin (Gas) and nitric oxide (NO) of the patients were the chief parameters observed before and after treatment.

RESULTS

There were arrhythmia of EGG, deficiency of MTL, Gas and NO in the patients with DFD, and these abnormal changes could be improved significantly by treating with HWC.

CONCLUSION

The abnormal gastric dynamics of the patients with DFD could be improved by HWC through multiple pathways.

Longitudinal follow-up of depressive symptoms among normal versus cognitively impaired elderly

OBJECTIVES

This prospectively designed longitudinal study assesses prevalence, incidence and prognosis of depressive symptoms among cognitively normal elderly volunteers compared with patients with mild cognitive impairment (MCI), dementia of Alzheimer type (DAT), and vascular dementia (VAD). Possible relationships between depressive symptoms, cognitive performance, disease types, and effects of antidepressant treatment were analyzed.

METHODS

Two hundred and ninety four subjects exhibiting different levels of cognitive performance were admitted to this study. Demographics, cardiovascular and neurodegenerative risk factors, together with measures of neuropsychological test performance, were obtained at sequential visits. Depressive symptoms were selectively treated with antidepressant medications.

RESULTS

One hundred and forty six subjects with normal cognition, 19 subjects with MCI, 42 patients with DAT, and 32 patients with VAD were followed for a mean of 3.5 years. With the passage of time, there were trends showing prevalence of depressive symptoms to decrease among DAT and to increase among VAD patients. VAD patients exhibited the highest incidences of new-onset depressive symptoms, followed in incidence by DAT and MCI groups. Depressive symptoms among VAD and MCI patients were more persistent and refractory to antidepressant medications than for DAT patients. Trends suggested that antidepressant treatment might benefit MCI and VAD subjects more than DAT patients. Motivationally related depressive symptoms accounted for major components of elevated Hamilton depression rating scale scores.

CONCLUSIONS

Depressive symptoms among DAT patients have higher rates of spontaneous resolution, without requiring intensive drug treatment, than among VAD patients in whom depressive symptoms are more persistent and refractory to drug treatment. Early depressive symptoms among subjects with MCI may represent a preclinical sign and should be considered as a risk factor for impending DAT or VAD among the elderly.

Verbenachalcone, a novel dimeric dihydrochalcone with potentiating activity on nerve growth factor-action from Verbena littoralis

A novel dimeric dihydrochalcone, verbenachalcone (1), was isolated from the aerial parts of Verbena littoralis. Its structure was elucidated, on the basis of spectral data interpretation, as 4,2',4',2' ",4' "-pentahydroxy-3' '-methoxy-3-O-4' '-tetrahydrobichalcone. This compound caused a significant enhancement of nerve growth factor-mediated neurite outgrowth from PC12D cells.

Potentiation of nerve growth factor-induced elongation of neurites by gelsemiol and 9-hydroxysemperoside aglucone in PC12D cells

In PC12D cells, nerve growth factor (NGF) increased the proportion of neurite-bearing cells and made neurites longer. A methanol extract of Verbena littoralis H. B. K. collected in Paraguay only slightly potentiated the proportion of PC12D cells with neurites but markedly increased the length of neurites in the presence of NGF (2 ng mL(-1)). The methanol extract was partitioned between ethyl acetate and water followed by further extraction of water fraction with n-butanol. The potentiating activity of NGF-action was observed in the ethyl acetate and n-butanol fractions. The n-butanol fraction was separated by silica gel chromatography, monitoring the NGF-potentiating activity to give gelsemiol and 9-hydroxysemperoside aglucone (9-OHSA). Neither compound (30-300 microM) exhibited neurite-inducing activity alone. Gelsemiol (100-300 microM) markedly enhanced an increase in the proportion of neurite-bearing cells and an extension of the neurite length in the presence of NGF (2 ng mL(-1)). Interestingly, in the presence of NGF (2 ng mL(-1)), 9-OHSA (100-300 microM) enhanced the elongation of neurites without affecting the increase in the proportion of cells with neurites. These results suggested that gelsemiol and 9-OHSA were major active components of V. littoralis in the NGF-potentiating action. It was possible that the mechanism of neurite elongation by NGF was different from that of the increase in the proportion of neurite-bearing cells, and that 9-OHSA selectively affected the neurite elongation mechanism.

HLA class II antigens positively and negatively associated with hepatosplenic schistosomiasis in a Chinese population

To identify possible associations between host genetic factors and the onset of liver fibrosis following Schistosoma japonicum infection, the major histocompatibility class II alleles of 84 individuals living on an island (Jishan) endemic for schistosomiasis japonica in the Poyang Lake Region of Southern China were determined. Forty patients exhibiting advanced schistosomiasis, characterised by extensive liver fibrosis, and 44 age and sex-matched control subjects were assessed for the class II haplotypes HLA-DRB1 and HLA-DQB1. Two HLA-DRB1 alleles, HLA-DRB1*0901 (P=0.012) and *1302 (P=0.039), and two HLA-DQB1 alleles, HLA-DQB1*0303 (P=0.012) and *0609 (P=0.037), were found to be significantly associated with susceptibility to fibrosis. These associated DRB1 and DQB1 alleles are in very strong linkage disequilibrium, with DRB1*0901-DQB1*0303 and DRB1*1302-DQB1*0609 found as common haplotypes in this population. In contrast, the alleles HLA-DRB1*1501 (P=0.025) and HLA-DQB1*0601 (P=0.022) were found to be associated with resistance to hepatosplenic disease. Moreover, the alleles DQB1*0303 and DRB1*0901 did not increase susceptibility in the presence of DQB1*0601, indicating that DQB1*0601 is dominant over DQB1*0303 and DRB1*0901. The study has thus identified both positive and negative associations between HLA class II alleles and the risk of individuals developing moderate to severe liver fibrosis following schistosome infection.

Helicobacter pylori infection induced alteration of gene expression in human gastric cells

BACKGROUND

Helicobacter pylori, a human pathogen responsible for many digestive disorders, induces complex changes in patterns of gene expression in infected tissues. cDNA expression arrays provide a useful tool for studying these complex phenomena.

AIM

To identify genes that showed altered expression after H pylori infection of human gastric cells compared with uninfected controls.

METHODS

The gastric adenocarcinoma cell line AGS was cocultivated with H pylori. Growth of infected cells was determined by trypan blue exclusion assay. Complementary DNA probes derived from H pylori treated and untreated cells were hybridised to two identical Atlas human cDNA expression arrays, and those genes with altered expression levels were identified. A real time quantitative reverse transcription-polymerase chain reaction assay was used to better define expression patterns of these genes in endoscopically gastric mucosal biopsies with and without H pylori infection.

RESULTS

Over 24 hours, coincubation with H pylori inhibited AGS cell growth but did not cause a noticeable degree of cell death. H pylori treatment altered the pattern of gene expression in AGS cells. We identified 21 overexpressed genes and 17 suppressed genes from the cDNA expression arrays. The majority of genes were transcription factors such as c-jun, BTEB2, and ETR101. Other genes were involved in signal transduction pathways, such as MAP kinase, interleukin 5, and insulin-like growth factor. Genes involved in cell cycle regulation and differentiation, such as CDC25B and NM23-H2, were also identified. In patients with H pylori infection (n=20), there was a significant difference for ERCC3, Id-2, and NM23-H2 mRNA levels in infected gastric mucosa compared with uninfected gastric mucosa in patients without peptic diseases (n=20) (ERCC3 4.75 molecules/10(4) beta-actin mRNA molecules v 13.65, p<0.001; Id-2 16.1 v 23.4, p<0.05; NM23-H2 17.5 v 45.5, p<0.001). There was no significant difference between mRNA levels of c-jun and CDC25B in H pylori colonised gastric mucosa and uninfected mucosa.

CONCLUSION

We demonstrated that H pylori infection caused alteration of gene expression in AGS cells. The differential hybridisation technique of Atlas human cDNA expression array is a useful method to identify host genes involved in pathogenic mechanisms in H pylori infection.

Validating mini-mental status, cognitive capacity screening and Hamilton depression scales utilizing subjects with vascular headaches

INTRODUCTION

The Mini-Mental State Examination (MMSE) and Cognitive Capacity Screening Examination (CCSE) are easily and rapidly administered tests for quantifying the general cognitive status of young as well as geriatric subjects. Likewise, the Hamilton Depression Rating Scale (HDRS) is a brief instrument for quantifying depression that may confound cognitive test performances. Testing by means of all three scales concurrently provides useful information for longitudinal research among the elderly.

OBJECTIVES

To validate the combined longitudinal use of MMSE, CCSE and HDRS among a specific cohort of normal subjects with vascular headaches characterized by known well-established temporary cognitive decline occurring only during temporary intervals with headache.

METHODS

The MMSE, CCSE and HDRS were serially tested at 3-12 monthly intervals among 196 healthy subjects attending our out-patient headache clinic who suffered from migraine or cluster headaches. Stability and specificity of MMSE, CCSE and HDRS were evaluated by comparing consecutive normative scores during headache-free intervals. Sensitivity of MMSE and CCSE for detecting temporary cognitive decline were evaluated by comparing scores during headache and headache-free intervals.

RESULTS

CCSE, MMSE and HDRS gave stable headache-free normative values over intervals of 3-10 years among 182 subjects. Among 77 subjects during headache intervals, temporary cognitive decline were confirmed by both CCSE and MMSE (p < 0.0001). When cutoff points for both CCSE and MMSE normal scores were placed at >/= 27, specificity for detecting cognitively normal values for CCSE and MMSE when headache-free were 92.2 and 89.6%, respectively (p > 0.05), while sensitivity for detecting cognitively decline during headache intervals were 83.7 and 49%, respectively (p < 0.001). Compared with scoring by a single rater, reliability estimates for all three rating scales were slightly lower when tested by different raters, but these differences were not significant.

CONCLUSIONS

CCSE is reliable and more sensitive than MMSE for detecting cognitive decline.

Response by B cell precursors to pre-B receptor assembly: differences between fetal liver and bone marrow

The expression of different sets of immunoglobulin specificities by fetal and adult B lymphocytes is a longstanding puzzle in immunology. In the past few years it has become clear that production of mu heavy chain and subsequent assembly with surrogate light chain to form the pre-B cell receptor complex is critical to promote development of adult B cell precursors in mouse bone marrow. Recently we found that instead of promoting pre-B cell expansion as in adult bone marrow, this complex inhibits pre-B cell growth in fetal liver, providing a previously unrecognized mechanism for alteration of the B cell repertoire with age. The consequence is very distinct primary repertoires for development of fetal B1 cells and adult bone marrow B2 cells.

Chemical forms of Pb, Zn and Cu in the sediment profiles of the Pearl River Estuary

The chemical forms of heavy metals (Pb, Zn and Cu) in sediment cores of the Pearl River Estuary were studied using a sequential chemical extraction method. The isotope ratios of 206Pb/207Pb in various chemical fractions were also measured to assess the potential Pb sources. Zinc and Cu were mainly associated with the residual fraction. The Fe-Mn oxide and organic/sulphide fractions were the next important phases for Zn and Cu, respectively. For Pb, different chemical partitioning patterns were found among different sediment cores. Most Pb was associated with the residual fraction in the sediments. In some sediment profiles, the major phase of Pb in the top layers was the Fe-Mn oxide fraction. The proportion of Pb in the Fe-Mn oxide fraction decreased significantly with increasing depth. Among the different depths, the 206Pb/207Pb isotope ratios in the residual fraction remained fairly stable, with a mean value of 1.202, which may represent the natural background value. The 206Pb/207Pb ratios in the exchangeable fraction were the lowest among the five fractions, particularly in top sediments, showing the anthropogenic inputs of heavy metals from recent rapid industrial development in the surrounding region. For the other three non-residual fractions, there was a similar trend of increasing 206Pb/207Pb ratios down the profile. Results from this study are useful in assessing both the chemical changes for heavy metals in marine sediments and the potential of heavy metal release into the water environment of an estuary area.

Sulfoglycolipid from the marine brown alga Sargassum hemiphylum

One kinds of glycolipid (SBI) have been isolated from the marine brown alga Sargassum hemiphyllum (Turn.) Ag. The structures of SBI have been determined as the sodium salt of 1-0-acyl-3-0-(6'-sulfo-alpha-D-quinovopyrannosyl) glycerol (acyl: tetradecanoyl, pentadecanoyl, 11-hexadecenoyl, hexadecanoyl, 10,13-octadecadienoyl, 9-octade cenoyl, 15-metylheptadecanoyl and 11-eicosenoyl 17: 1.5: 19: 153: 1: 19: 1: 2) on the basis of chemical and spectral evidence and GC-MS analysis, respectively. Four constituents of the SBI were new compounds [the sodium salt of 1-0-(11"-hexadecenoyl)-3-0-(6'-sulfo-alpha-D-quinovopyrannosyl) glycerol, the sodium salt of 1-0-(10",13"-octadecadienoyl)-3-0-(6'-sulfo-alpha-D-quinovopyrannosyl) glycerol, and the sodium salt of 1-0-(15"-metylhexadecenoyl)-3-0-(6'-sulfo-alpha-D-quinovopyrannosyl) glycerol, and the sodium salt of 1-0-(11"-eicosenoyl)-3-0-(6'-sulfo-alpha-D-quinovopyrannosyl) glycerol]. All compounds were isolated from marine brown alga for the first time.

Interfacial study of benzenesulfinate chemisorbed on silver

The oxidative stability of self-assembled monolayer (SAM) of thiols on silver was examined with matrix-assisted laser desorption ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS). A benzenesulfinate (BS) monolayer on silver was also prepared and investigated with MALDI-TOF-MS and surface-enhanced Raman scattering (SERS). The presence of sulfinate, sulfonate, and thiosulfonate fragment ions reveals that thiolate monolayers oxidize in the air. The relative abundance of C6H5SO2- and C6H5SO3- species in the mass spectra of the monolayer with different air-exposure times provides an estimation of the oxidation progress. In the vibrational spectrum, the large red shift of v(SOO-), combined with the lack of a shift of v(C-S) upon adsorption, indicates its bidentate O-coordination. The orientation of the confined molecules, based on the Raman surface selection rules, was derived from the preferential enhancement of the different functional groups. The benzene ring of BS was found almost normal to the metal surface as a result of the intermolecular forces; that geometry excludes the possibility of the pi-system of the benzene ring from participating as another binding site. The SER spectra of BS obtained via a selective etching process confirms these observations.

Effects of active and negative mutants of Ras on rat arterial neointima formation

BACKGROUND

Ras protein is a key signal transducer in the cause of cell proliferation. We studied the effects of active and negative mutants of the Ras gene on arterial neointimal formation in rats, with the aim of elucidating the molecular mechanisms regulating restenosis following percutaneous transluminal coronary angioplasty.

MATERIALS AND METHODS

AdRasV12 and AdRasN17, the recombinant adenoviruses containing a constitutively active mutant and a dominant negative mutant of Ras, respectively, were used to determine whether Ras is necessary and sufficient to modulate the smooth muscle cell proliferation and neointima formation. Following balloon injury, rat common carotid arteries were treated in their distal half with AdRasV12, AdRasN17, or AdLacZ, with the proximal half used as uninfected control.

RESULTS

In rat arteries subjected to balloon injury, either uninfected or treated with AdLacZ, there were pronounced SMC proliferation and neointima formation. These changes were markedly augmented by AdRasV12 and reduced by AdRasN17.

CONCLUSION

Ras is necessary and sufficient for SMC proliferation and neointima formation and may play a critical role in restenosis following balloon angioplasty.

Surface-enhanced raman spectra of some anti-tubercle bacillus drugs

Surface-enhance Raman (SER) spectra of pyrazinamide (PZA), isoniazid (INAZ), and isonicotiamide (INCT) in silver sols have been studied over a range of solution concentration and pH. A linear calibration curve has been obtained for each of the sample molecules, and the lower limits of detection are estimated to be 5 ng for PZA and INAZ, and 10 ng for INCA. The variation of SER intensity with the sample solution pH is explained in terms of the charge of the sample species and the stability of the sols. The normal Raman and infrared spectra for the pure drug samples have also been collected, from which some vibration assignments for the molecules are given. The absorption behaviors of the molecules on the silver particle surfaces are also suggested.

Biomechanical regulation of matrix metalloproteinase-9 in cultured chondrocytes

Abnormal mechanical loading of joints may induce degeneration of articular cartilage. Shear stress is one mode of mechanical loading that may regulate chondrocyte metabolism. We investigated the mechanism by which shear stress induces the gene encoding matrix metalloproteinase-9, a mediator of the progressive degradation of articular cartilage in osteoarthritis. In vitro experiments using passaged rabbit chondrocytes in monolayer culture subjected to a shear stress of 16 dyn/cm2 (1.6 Pa) in a flow channel showed increased expression of the matrix metalloproteinase-9 gene. The induction of matrix metalloproteinase-9 appeared to depend on a region in the 5' promoter of the gene that contains a 12-0-tetradecanoylphorbol 13-acetate-responsive element. Transfection experiments using a construct containing a luciferase reporter driven by a 12-0-tetradecanoylphorbol 13-acetate-responsive element indicated that shear stress activated a 12-0-tetradecanoylphorbol 13-acetate-responsive element-mediated transcription in chondrocytes. Similar experiments showed that shear stress induced a matrix metalloproteinase-9 promoter construct (matrix metalloproteinase-9-luciferase). Shear stress activated c-Jun NH2-terminal kinase, extracellular signal-regulated kinase, and p38. Transfection of matrix metalloproteinase-9-luciferase together with the dominant negative mutant of c-Jun NH2-terminal kinase, but not with that of extracellular signal-regulated kinase or p38, attenuated the shear-induced matrix metalloproteinase-9 promoter activity. In addition, transfection of constructs encoding dominant negative mutants of Ras, Rac, and Cdc42 attenuated the induction of c-Jun transcriptional activity by shear stress. Thus. shear stimulation of chondrocytes stimulates Ras, Rac, and Cdc42, which subsequently activate c-Jun NH2-terminal kinase to induce a 12-0-tetradecanoylphorbol 13-acetate-responsive element-mediated expression of matrix metalloproteinase-9.

Surface-enhanced raman spectra of dyes and organic acids in silver solutions: chloride ion effect

We have recorded surface-enhanced Raman (SER) spectra of two different classes of compounds, cationic dyes and organic acids, and studied their chloride ion effects on the surface-enhanced Raman scattering (SERS) activities of the silver solution. For the positive charge dyes, rhodamine 6G (R6G) and 1,1'-dimethyl-2,2'-cyanine iodide (DECI), no SERS could be observed without the addition of chloride ions because of lack of the electrostatic interaction between the dye species and the silver particles in the silver solution. The chloride ions served to enlarge silver particles and to contribute the existence of the surface active sites, making the silver solution SERS active to the dye samples. Surface-enhanced resonance Raman scattering (SERRS) intensity of the dye molecules increased with the chloride ion concentration. After reaching a maximum intensity, a Cl- quenching effect on the intensity took place. For the organic acids, benzoic acid and p-aminobenzoic acid (PABA), SERS could be observed without the coexistence of chloride ions. The intensity of the Raman scattering did not vary significantly in the presence of small amount of chloride ion. At high Cl- concentration, quenching SERS intensity began to take effect.

Competition in the presence of a lethal external inhibitor

The study considers two organisms competing for a nutrient in an open system in the presence of an inhibitor (or toxicant). The inhibitor is input at a constant rate and is lethal to one competitor while being taken up by the other without harm. This is in contrast to previous studies, where the inhibitor decreases the reproductive rate of one of the organisms. The mathematical result of the lethal effect, modeled by a mass action term, is that the system cannot be reduced to a monotone dynamical system of one order lower as is common with chemostat-like problems. The model is described by four non-linear, ordinary differential equations and we seek to describe the asymptotic behavior as a function of the parameters of the system. Several global exclusion results are presented with mathematical proofs. However, in the case of coexistence, oscillatory behavior is possible and the study proceeds with numerical examples. The model is relevant to bioremediation problems in nature and to laboratory bio-reactors.