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At least 595 records · Page 33Linked to original sources
PubMed2002

Performances and limits of a parallel oscillator for electrochemical quartz crystal microbalances.

This paper describes a driving circuit for an electrochemical quartz crystal microbalance (EQCM) adapted to a wide range of applications. The oscillator is a Miller-type parallel oscillator using an operational transconductance amplifier (OTA). A theoretical study of the oscillating circuit led to the analytical expression of the microbalance frequency as well as to an overestimation of the error on the mass measurement. The reliability of the EQCM was then experimentally verified through electrochemical copper deposition and dissolution. The limit of operation of the EQCM was also investigated, both analytically and experimentally. This work shows that parallel oscillators using few electronic components allow a very reliable EQCM to be obtained for mass measurements on metallic films, even if they are highly damped.

Journal Article↗
PubMed2002

Rapid, specific determination of iodine and iodide by combined solid-phase extraction/diffuse reflectance spectroscopy.

A new, rapid methodology for trace analysis using solid-phase extraction is described. The two-step methodology is based on the concentration of an analyte onto a membrane disk and on the determination by diffuse reflectance spectroscopy of the amount of analyte extracted on the disk surface. This method, which is adaptable to a wide range of analytes, has been used for monitoring ppm levels of iodine and iodide in spacecraft water. Iodine is used as a biocide in spacecraft water. For these determinations, a water sample is passed through a membrane disk by means of a 10-mL syringe that is attached to a disk holder assembly. The disk, which is a polystyrene-divinylbenzene composite, is impregnated with poly(vinylpyrrolidone) (PVP), which exhaustively concentrates iodine as a yellow iodine-PVP complex. The amount of concentrated iodine is then determined in only 2 s by using a hand-held diffuse reflectance spectrometer by comparing the result with a calibration curve based on the Kubelka-Munk function. The same general procedure can be used to determine iodide levels after its facile and exhaustive oxidation to iodine by peroxymonosulfate (i.e., Oxone reagent). For samples containing both analytes, a two-step procedure can be used in which the iodide concentration is calculated from the difference in iodine levels before and after treatment of the sample with peroxymonosulfate. With this methodology, iodine and iodide levels in the 0.1-5.0 ppm range can be determined with a total workup time of approximately 60 s with a RSD of approximately 6%.

Colorimetry↗
PubMed1976

Purification of proteins from the 50S ribosomal subunit of Escherichia coli by ion-exchange chromatography.

Thirty-three proteins have been isolated from the 50S ribosomal subunit of Escherichia coli by a technique based solely upon ion-exchange chromatography. The procedure can be adapted to a wide range of sample sizes, requires no prefractionation of the subunit proteins, and employs readily regenerated chromatographic media. The molecular weights, purity, and immunological properties of the individual proteins have been characterized. More than 20 of the proteins were judged to be at least 95% pure by electrophoretic analysis; the remaining proteins were generally over 90% pure. Methods for the immunological identification of small amounts of ribosomal proteins are described.

Chromatography, Ion Exchange↗
PubMed2003

HIV-1 vaccine development: constrained peptide immunogens show improved binding to the anti-HIV-1 gp41 MAb.

The human immunodeficiency virus type I (HIV-1) transmembrane glycoprotein gp41 mediates viral entry through fusion of the target cellular and viral membranes. A segment of gp41 containing the sequence Glu-Leu-Asp-Lys-Trp-Ala has previously been identified as the epitope of the HIV-1 neutralizing human monoclonal antibody 2F5 (MAb 2F5). The 2F5 epitope is highly conserved among HIV-1 envelope glycoproteins. Antibodies directed at the 2F5 epitope have neutralizing effects on a broad range of laboratory-adapted HIV-1 variants and primary isolates. Recently, a crystal structure of the epitope bound to the Fab fragment of MAb 2F5 has shown that the 2F5 peptide adopts a beta-turn conformation [Pai, E. F., Klein, M. H., Chong, P., and Pedyczak, A. (2000) World Intellectual Property Organization Patent WO-00/61618]. We have designed cyclic peptides to adopt beta-turn conformations by the incorporation of a side-chain to side-chain lactam bridge between the i and i + 4 residues containing the Asp-Lys-Trp segment. Synthesis of extended, nonconstrained peptides encompassing the 2F5 epitope revealed that the 13 amino acid sequence, Glu-Leu-Leu-Glu-Leu-Asp-Lys-Trp-Ala-Ser-Leu-Trp-Asn, maximized MAb 2F5 binding. Constrained analogues of this sequence were explored to optimize 2F5 binding affinity. The solution conformations of the constrained peptides have been characterized by NMR spectroscopy and molecular modeling techniques. The results presented here demonstrate that both inclusion of the lactam constraint and extension of the 2F5 segment are necessary to elicit optimal antibody binding activity. The ability of these peptide immunogens to stimulate a high titer, peptide-specific immune response incapable of viral neutralization is discussed in regard to developing an HIV-1 vaccine designed to elicit a 2F5-like immune response.

AIDS Vaccines↗
PubMed2002

Predicting gas transport in formed zeolite adsorbents from NMR studies.

The self-diffusion of nitrogen, methane, and carbon monoxide within a 5A zeolitic adsorbent has been examined with use of pulsed field gradient (PFG) NMR. In all cases, the diffusion process is well-described by a refined version of the long-range diffusion model (LRDM), adapted here for use with pelletized adsorbents, which uses exclusively adsorbent porosity and isotherm data as inputs. Correlation of the experimental data with this model yields tortuosity factors that are characteristic of the adsorbate and reflect the longer diffusive path a molecule must take due to the winding nature of the pore structure. It is demonstrated that the diffusion model can be used to accurately predict the diffusion coefficients for a ternary gas mixture within a 5A zeolite. To fully characterize the diffusive process, the surface excess on the PFG NMR samples has been obtained by a novel gas-phase NMR technique that is well-suited for measuring pure and multicomponent isotherms.

Journal Article↗
PubMed2006

Profiling the near field of a plasmonic nanoparticle with Raman-based molecular rulers.

The enhanced local optical fields at the surface of illuminated metallic nanoparticles and nanostructures are of intense fundamental and technological interest. Here we report a self-consistent measurement of the spatial extent of the fringing field above a plasmonic nanoparticle surface. Bifunctional DNA-based adsorbate molecules are used as nanoscale optical rulers, providing two distinct surface enhanced Raman scattering signals that vary independently in intensity as a function of distance from the nanoparticle surface. While the measurement technique is calibrated on gold nanoshell surfaces with controlled and predictable electromagnetic nanoenvironments, this approach is broadly adaptable to a wide range of plasmonic geometries.

DNA↗
PubMed2025

Chromosome-level genome assembly of starry flounder (Platichthys stellatus).

Starry flounder (Platichthys stellatus) is widely distributed along the coastlines of the North Pacific. As an euryhaline flatfish, it can adapt to a wide range of environmental salinity ranging from freshwater to seawater, and is a promising aquaculture flatfish species in Korea and North China. However, no high-quality starry flounder reference genome has been reported to date, which greatly limits the studies of genetics and functional genomics. Here, we obtained a high-quality chromosome-level starry flounder genome assembly with a length of 643.56 Mb (scaffold N50: 26.19 Mb, contig N50: 10.00 Mb) combining short-reads sequencing, PacBio HiFi sequencing, and Hi-C sequencing. Approximately 94.02% of assembled sequences were anchored into 24 pseudochromosomes, and a total of 18 telomeres were detected. Totally 22,835 protein-coding genes and 227.87 Mb repetitive sequences were identified. In summary, the high-quality chromosome-level genome assembly not only provides valuable resources for genetic research in starry flounder, but also advances the development of molecular breeding technology of starry flounder.

Animals↗
PubMed2001

Indigenous domestic breeds as reservoirs of genetic diversity: the Argentinean Creole cattle.

Contrary to highly selected commercial breeds, indigenous domestic breeds are composed of semi-wild or feral populations subjected to reduced levels of artificial selection. As a consequence, many of these breeds have become locally adapted to a wide range of environments, showing high levels of phenotypic variability and increased fitness under natural conditions. Genetic analyses of three loci associated with milk production (alpha(S1)-casein, kappa-casein and prolactin) and the locus BoLA-DRB3 of the major histocompatibility complex indicated that the Argentinean Creole cattle (ACC), an indigenous breed from South America, maintains high levels of genetic diversity and population structure. In contrast to the commercial Holstein breed, the ACC showed considerable variation in heterozygosity (H(e)) and allelic diversity (A) across populations. As expected, bi-allelic markers showed extensive variation in He whereas the highly polymorphic BoLA-DRB3 showed substantial variation in A, with individual populations having 39-74% of the total number of alleles characterized for the breed. An analysis of molecular variance (AMOVA) of nine populations throughout the distribution range of the ACC revealed that 91.9-94.7% of the total observed variance was explained by differences within populations whereas 5.3-8.1% was the result of differences among populations. In addition, the ACC breed consistently showed higher levels of genetic differentiation among populations than Holstein. Results from this study emphasize the importance of population genetic structure within domestic breeds as an essential component of genetic diversity and suggest that indigenous breeds may be considered important reservoirs of genetic diversity for commercial domestic species.

Alleles↗
PubMed2001

A dual path programmable array microscope (PAM): simultaneous acquisition of conjugate and non-conjugate images.

A programmable array microscope (PAM) incorporates a spatial light modulator (SLM) placed in the primary image plane of a widefield microscope, where it is used to define patterns of illumination and/or detection. We describe the characteristics of a special type of PAM collecting two images simultaneously. The conjugate image (Ic) is formed by light originating from the object plane and returning along the optical path of the illumination light. The non-conjugate image (Inc) receives light from only those regions of the SLM that are not used for illuminating the sample. The dual-signal PAM provides much more time-efficient excitation than the confocal laser scanning microscope (CLSM) and greater utilization of the available emission light. It has superior noise characteristics in comparison to single-sided instruments. The axial responses of the system under a variety of conditions were measured and the behaviour of the novel Inc image characterized. As in systems in which only Ic images are collected (Nipkow-disc microscopes, and previously characterized PAMs), the axial response to thin fluorescent films showed a sharpening of the axial response as the unit cell of the repetitive patterns decreased in size. The dual-signal PAM can be adapted to a wide range of data analysis and collection strategies. We investigated systematically the effects of patterns and unit cell dimensions on the axial response. Sufficiently sparse patterns lead to an Ic image formed by the superposition of the many parallel beams, each of which is equivalent to the single scanning spot of a CLSM. The sectioning capabilities of the system, as given by its axial responses, were similar for a given scan pattern and for processed pseudorandom sequence (PRS) scans with the same size of the unit cell. For the PRS scans, optical sectioning was achieved by a subtraction of an Inc image or, alternatively, a scaled widefield image from the Ic image. Based on the comparative noise levels of the two methods, the non-conjugate subtraction was significantly superior. A point spread function for Ic and Inc was simulated and properties of the optical transfer functions (OTFs) were compared. Simulations of the OTF in non-conjugate imaging did not suffer from the missing cone problem, enabling a high quality deconvolution of the non-conjugate side alone. We also investigated the properties of images obtained by subjecting the Ic and Inc data to a combined maximum likelihood deconvolution.

Animals↗
PubMed2002

A new high-aperture glycerol immersion objective lens and its application to 3D-fluorescence microscopy.

High-resolution light microscopy of glycerol-mounted biological specimens is performed almost exclusively with oil immersion lenses. The reason is that the index of refraction of the oil and the cover slip of approximately 1.51 is close to that of approximately 1.45 of the glycerol mountant, so that refractive index mismatch-induced spherical aberrations are tolerable to some extent. Here we report the application of novel cover glass-corrected glycerol immersion lenses of high numerical aperture (NA) and the avoidance of these aberrations. The new lenses feature a semi-aperture angle of 68.5 degrees, which is slightly larger than that of the diffraction-limited 1.4 NA oil immersion lenses. The glycerol lenses are corrected for a quartz cover glass of 220 microm thickness and for a 80% glycerol-water immersion solution. Featuring an aberration correction collar, the lens can adapt to glycerol concentrations ranging between 72% and 88%, to slight variations of the temperature, and to the cover glass thickness. As the refractive index mismatch-induced aberrations are particularly important to quantitative confocal fluorescence microscopy, we investigated the axial sectioning ability and the axial chromatic aberrations in such a microscope as well as the image brightness as a function of the penetration depth. Whereas there is a significant decrease in image brightness associated with oil immersion, this decrease is absent with the glycerol immersion system. In addition, we show directly the compression of the optic axis in the case of oil immersion and its absence in the glycerol system. The unique advantages of these new lenses in high-resolution microscopy with two coherently used opposing lenses, such as 4 Pi-microscopy, are discussed.

Animals↗
PubMed2004

[Pustular diseases of the newborn].

In the newborn, there exists a wide spectrum of pustular skin diseases. These range from transitory, benign adaptation disorders up to systemic, life threatening illnesses. In 30-60% of newborns pustules are observed in association with the relatively harmless Erythema toxicum, the origin of which is still unknown today. It is necessary to differentiate this from the pustular diseases which may be of infectious or non-infectious nature and which require therapy. Typical pathogens include Malassezia furfur, Staphylococci, Streptococci, Candida spp. and the herpes virus group.

Diagnosis, Differential↗
PubMed2003

Accuracy of weighing simulated infants with in-bed and freestanding scales while connected and disconnected to a ventilator.

PURPOSE: To develop an accurate method of weighing ventilated infants in the clinical setting. SUBJECTS: Two dolls that simulated ventilated infants were adapted to different weights ranging from 745 to 3,995 g. DESIGN: Four methods of weighing ventilated infants were evaluated. The study design used multiple clinical nurses, randomly chosen, to weigh the simulated infants. Freestanding and in-bed scales were used with a simulated ventilated infant being either connected or disconnected from the ventilator tubing for the procedure. RESULTS: The mean weights of the simulated infants measured in the incubator, with or without the ventilator connected, had a mean difference of +/- 2 g from the gold standard. However, the mean weights of the simulated infants measured on the freestanding scales were 12 g < the gold standard of industry calibrated weights (P < 0.001). The measurement error was small both with and without the ventilator connected. This error was proportionally very small for weights over 1,500 g, but was increased for weights < 1,500 g. CONCLUSION: The use of in-bed scales was the most accurate method of weighing simulated infants of all weight categories. This study shows the importance of a consistent and meticulous technique when weighing infants in intensive care. The accuracy of weights is enhanced with the use of in-bed scales, and this is particularly significant in infants less than 1,500 g.

Body Weight↗
PubMed2000

Dietary management of feline chronic renal failure: where are we now? In what direction are we headed?

Dietary modification is of primary importance in managing cats with chronic renal failure. Diets designed for cats with chronic renal failure are typically formulated to be pH neutral and contain reduced quantities of protein, phosphorus and sodium and an increased quantity of potassium. These changes in diet formulation are designed to ameliorate clinical signs of renal failure by adapting dietary intakes to meet the limited ability of failing kidneys to adapt to the normal range of dietary intakes. Important recent clinical trials support the therapeutic value of dietary therapy in cats with chronic renal failure.

Acidosis↗
PubMed2003

Host defense reinforces host-parasite cospeciation.

Cospeciation occurs when interacting groups, such as hosts and parasites, speciate in tandem, generating congruent phylogenies. Cospeciation can be a neutral process in which parasites speciate merely because they are isolated on diverging host islands. Adaptive evolution may also play a role, but this has seldom been tested. We explored the adaptive basis of cospeciation by using a model system consisting of feather lice (Columbicola) and their pigeon and dove hosts (Columbiformes). We reconstructed phylogenies for both groups by using nuclear and mitochondrial DNA sequences. Both phylogenies were well resolved and well supported. Comparing these phylogenies revealed significant cospeciation and correlated evolution of host and parasite body size. The match in body size suggested that adaptive constraints limit the range of hosts lice can use. We tested this hypothesis by transferring lice among hosts of different sizes to simulate host switches. The results of these experiments showed that lice cannot establish viable populations on novel hosts that differ in size from the native host. To determine why size matters, we measured three components of louse fitness: attachment, feeding, and escape from host defense (preening). Lice could remain attached to, and feed on, hosts varying in size by an order of magnitude. However, they could not escape from preening on novel hosts that differed in size from the native host. Overall, our results suggest that host defense reinforces cospeciation in birds and feather lice by preventing lice from switching between hosts of different sizes.

Animals↗
PubMed1998

Differential patterns of acquired virulence genes distinguish Salmonella strains.

Analysis of several Salmonella typhimurium in vivo-induced genes located in regions of atypical base composition has uncovered acquired genetic elements that cumulatively engender pathogenicity. Many of these regions are associated with mobile elements, encode predicted adhesin and invasin-like functions, and are required for full virulence. Some of these regions distinguish broad host range from host-adapted Salmonella serovars and may contribute to inherent differences in host specificity, tissue tropism, and disease manifestation. Maintenance of this archipelago of acquired sequence by selection in specific hosts reveals a fossil record of the evolution of pathogenic species.

Animals↗
PubMedDate not supplied

Technical note. A design study of a bioelectric amplifier and improvement of its parameters.

A design study of a bioelectric amplifier that has better parameters than conventional designs is presented. The design allows the construction of bioelectric amplifiers with improved parameters in terms of noise, common mode rejection ratio, and input impedance. The voltage gain and bandwidth are easily adapted to a wide range of biomedical applications. The experimental results of the designed bioelectric amplifier are also included.

Algorithms↗
PubMed1951

Frequency of seeing functions for intensity discrimination of various levels of adapting intensity.

1. The percentage of times a human subject detects an increment (DeltaI) in intensity was determined as a function of the magnitude of the increment and the magnitude of the stimulus (I) to which the increment is added. 2. Foveal stimulation was used, and five frequency of seeing curves were obtained at each of nine values of adapting intensity covering the range from -1.45 to 4.45 log photons. Each frequency of seeing curve shows the percentage of times an increment in intensity is detected as a function of the logarithm of the increment. 3. The slope of the frequency of seeing curve increases slightly with an increase in I and finally becomes independent of I at medium to high intensities. 4. The implications of the results for quantum theories of visual excitation are considered.

Humans↗
PubMed2005

Experimental evolution of Pseudomonas fluorescens in simple and complex environments.

In complex environments that contain several substitutable resources, lineages may become specialized to consume only one or a few of them. Here we investigate the importance of environmental complexity in determining the evolution of niche width over approximately 900 generations in a chemically defined experimental system. We propagated 120 replicate lines of the bacterium Pseudomonas fluorescens in environments of different complexity by using between one and eight carbon substrates in each environment. Genotypes from populations selected in complex environments evolved greater mean and variance in fitness than those from populations selected in simple environments. Thus, lineages were able to adapt to several substrates simultaneously without any appreciable loss of function with respect to other substrates present in the media. There was greater genetic and genotype-by-environment interaction variance for fitness within populations selected in complex environments. It is likely that genetic variance in populations grown on complex media was maintained because the identity of the fittest genotype varied among carbon substrates. Our results suggest that evolution in complex environments will result neither in narrow specialists nor in complete generalists but instead in overlapping imperfect generalists, each of which has become adapted to a certain range of substrates but not to all.

Bacterial Typing Techniques↗