Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “electrostatics”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35Linked to original sources
PubMed2002

Reducing airborne pathogens, dust and Salmonella transmission in experimental hatching cabinets using an electrostatic space charge system.

Electrostatic charging of particles in enclosed spaces has been shown to be an effective means of reducing airborne dust. Dust generated during the hatching process has been strongly implicated in Salmonella transmission, which complicates the cleaning and disinfecting processes for hatchers. Following two preliminary trials in which dust reduction was measured, four trials were conducted to evaluate the effectiveness of an electrostatic space charge system (ESCS) on the levels of total aerobic bacteria (TPC), enterobacteriaceae (ENT), and Salmonella within an experimental hatching cabinet. The ESCS was placed in a hatching cabinet that was approximately 50% full of 18-d-old broiler hatching eggs. The ESCS operated continuously to generate a strong negative electrostatic charge throughout the cabinet through hatching, and dust was collected in grounded trays containing water and a degreaser. An adjacent hatching cabinet served as an untreated control. Air samples from hatchers were collected daily, and sample chicks from each hatcher were grown out to 7 d of age for cecal analysis in three of the trials. The ESCS significantly (P < 0.05) reduced TPC and ENT by 85 to 93%. Dust concentration was significantly reduced (P < 0.0001) during the preliminary trials with an average reduction of 93.6%. The number of Salmonella per gram of cecal contents in birds grown to 7 d of age was significantly (P < 0.001) reduced by an average log10 3.4 cfu/g. This ionization technology is relatively inexpensive and could be used to reduce airborne bacteria and dust within the hatching cabinet.

Air Microbiology↗
PubMed2004

Evaluation of culture media for detecting airborne Salmonella enteritidis collected with an electrostatic sampling device from the environment of experimentally infected laying hens.

Detection of Salmonella enteritidis in the environment of commercial laying hens is critical for reducing the production of contaminated eggs by infected flocks. In the present study, an inexpensive and portable electrostatic air sampling device was used to collect S. enteritidis in rooms containing experimentally infected laying hens. After hens were orally inoculated with a phage type 13a S. enteritidis strain and housed in individual cages, air samples were collected 3 times each week with electrostatic devices onto plates of 6 types of culture media (brilliant green agar, modified lysine iron agar, modified semisolid Rappaport-Vassiliadis agar, Rambach agar, XLD agar, and XLT4 agar). Air sampling plates were incubated at 37 degrees C, examined visually for presumptive identification of typical S. enteritidis colonies and then subjected to confirmatory enrichment culturing. Air samples (collected using all 6 culture media) were positive for S. enteritidis for 3 wk postinoculation. Because visual determination of the presence or absence of typical S. enteritidis colonies on air sampling plates was not consistently confirmed by enrichment culturing, the postenrichment results were used for comparing sampling strategies. The frequency of positive air sampling results using brilliant green agar (66.7% overall) was significantly greater than was obtained using most other media. A combination of several plating media (brilliant green agar, modified lysine iron agar, and XLT4 agar) allowed detection of airborne S. enteritidis at an overall frequency of 83.3% over the 3 wk of sampling. When used with appropriate culture media, electrostatic collection of airborne S. enteritidis can provide a sensitive alternative to traditional methods for detecting this pathogen in the environment of laying flocks.

Air Microbiology↗
PubMed1985

Dependence of electrostatic diffusion of Rn progeny on environmental parameters.

In previous work it was established that electrostatic diffusion of Rn progeny attached to aerosols can be used for passive dosimetry by replacing the pump-filter assembly in an active dosimeter by an electret. In the present work, results are presented on the dependence of activity collected by an electret on aerosol concentration, aerosol diameter, attachment rate of Rn progeny to aerosols, unattached fraction of Rn progeny, and Rn progeny concentrations. The electrostatic flow rate of Rn progeny is defined and all relationships analyzed in terms of this flow rate. The electrostatic flow rate is found to be reasonably constant for 0.03 micron less than particle diameter less than 0.09 micron, unattached fraction of 218Po less than 0.40 and 70,000/cm3 less than aerosol concentration less than 180,000/cm3; experimentally obtained data outside these limits are too few to draw any definite conclusions. The results are useful from a practical point of view because typical U mine conditions are described by these limits.

Aerosols↗
PubMedDate not supplied

Phosphate clearance for bleach reprocessed polysulfone hemodialyzers: effects of electrostatic interactions.

Hyperphosphatemia is a major problem for hemodialysis patients due to inadequate phosphate clearance during dialysis. The objective of this study was to understand the effects of bleach reprocessing on phosphate clearance. Data were obtained using Fresenius polysulfone dialyzers exposed to bleach in an in vitro dialysis. The phosphate clearance decreased slightly after a single reprocessing cycle, with more than a 10% reduction observed after 15 cycles. Streaming potential measurements showed that bleach reprocessing caused an increase in the negative charge on the polysulfone membrane, suggesting that the change in phosphate clearance was due to an increase in electrostatic repulsion. The changes in clearance and surface charge were consistent with theoretical calculations of the effects of electrostatic interactions on solute diffusion. These results provide the first evidence that bleach reprocessing can reduce phosphate clearance due to electrostatic interactions between the phosphate anion and negatively charged dialysis membranes.

Equipment Reuse↗
PubMed1980

Electrostatic components of drug-receptor recognition. II. The DNA-binding antibiotic actinomycin.

The semiempirical molecular orbital method PCILO has been used to study the electronic charge distribution and conformation of the antibiotic actinomycin. Molecular electrostatic potential fields have been constructed in three-dimensional space round the molecule and displayed stereoscopically together with contour maps in the orthogonal planes relative to that of the chromophore. It was found that the drug has a considerable dipole moment and that the electrostatic fields can be separated into two large regions; an area of positive potential surrounds the chromophore and one of negative potential is directed away from the peptide rings. In this and the preceding paper these observations are discussed with respect to drug-receptor recognition phenomena. Pattern-matching of complementary electrostatic fields between the drug and polynucleotide receptor can be discerned.

Chemical Phenomena↗
PubMed1999

Negative electrostatic contribution to the bending rigidity of charged membranes and polyelectrolytes screened by multivalent counterions.

Bending rigidity of a charged membrane or polyelectrolyte screened by monovalent counterions is known to be enhanced by electrostatic effects. We show that in the case of screening by multivalent counterions the electrostatic effects reduce the bending rigidity. This inversion of the sign of the electrostatic contribution is related to the formation of two-dimensional strongly correlated liquids (SCL) of counterions at the charged surface due to strong lateral repulsion between them. When a membrane or a polyelectrolyte is bent, SCL is compressed on one side and stretched on the other so that thermodynamic properties of SCL contribute to the bending rigidity. Thermodynamic properties of SCL are similar to those of Wigner crystal and are anomalous in the sense that the pressure, compressibility and screening radius of SCL are negative. This brings about substantial negative correction to the bending rigidity. For the case of DNA this effect qualitatively agrees with experiment.

Cations↗
PubMed2000

Electrostatic interaction between two charged dielectric spheres in contact

Of fundamental importance in numerous industrial and natural processes, the problem of two electrified spheres has been studied by many authors. However, the problem of particular importance for understanding electrostatic effects on powder or granular behavior, such as two dielectric spheres both carrying arbitrary amounts of charge, is still open for investigation. In the present work, two touching dielectric spheres of equal size and permittivity but arbitrary amounts of charge are studied by computational means of the Galerkin finite-element method. The effects of permittivity and the ratio of charge on the spheres are the main focus here. Because of the electric polarization, the electrostatic force can become attractive even when the two spheres carry charges of the same sign, due to positive dielectric effects, or to become repulsive for spheres with charges of the opposite sign, due to negative dielectric effects. In the presence of dielectrophoretic effect, whether the electrostatic force between the two spheres is attractive or repulsive is found to be determined by the ratio of charge on the two spheres.

Journal Article↗
PubMed2002

Electrostatic fluctuations in soap films.

A field theory to describe electrostatic interactions in soap films, described by electric multilayers with a generalized thermodynamic surface-charging mechanism, is studied. In the limit where the electrostatic interactions are weak, this theory is exactly soluble. The theory incorporates in a consistent way, the surface-charging mechanism and the fluctuations in the electrostatic field that correspond to the zero-frequency component of the van der Waals force. It is shown that these terms lead to a Casimir-like attraction that can be sufficiently large to explain the transition between the common black film to a Newton black film.

Journal Article↗
PubMed2002

Electrostatic force in prometaphase, metaphase, and anaphase-A chromosome motions.

Primitive cells had to divide using very few biological mechanisms. This work proposes physicochemical mechanisms, based upon nanoscale electrostatics, which explain and unify the motions of chromosomes during prometaphase, metaphase, and anaphase A. In the cytoplasmic medium that exists in biological cells, electrostatic fields are subject to strong attenuation by ionic screening, and therefore decrease rapidly over a distance equal to several Debye lengths. However, the presence of microtubules within cells completely changes the situation. Microtubule dimer subunits are electric dipolar structures, and can act as intermediaries that extend the reach of the electrostatic interaction over cellular distances. Experimental studies have shown that intracellular pH rises to a peak at mitosis, then decreases through cytokinesis. This result, in conjunction with the electric dipole nature of microtubule subunits, is sufficient to explain the dynamics of the above mitotic motions, including their timing and sequencing. The physicochemical mechanisms utilized by primitive eukaryotic cells could provide important clues regarding our understanding of cell division in modern eukaryotic cells.

Anaphase↗
PubMed2005

Magnetic-field effects on nonlinear electrostatic-wave Landau damping.

A numerical code, which solves the Vlasov-Poisson system of equations for an electron magnetized plasma with motionless ions, is presented. The numerical integration of the Vlasov equation has been performed using the "splitting method" and the cylindric geometry in the velocity space is used to describe the motion of the particles around the external field. The time evolution of an electrostatic wave, propagating perpendicularly to the background magnetic field, is numerically studied in both the linear and nonlinear regimes, for different values of the ratio gamma between the electron oscillation time in a sinusoidal potential well and the electron cyclotron period. It is shown that the external magnetic field plays very different roles, depending on the values of the initial wave amplitude. When the initial amplitude is less than some threshold, the magnetic field prevents the Landau damping of the electrostatic wave (Bernstein-Landau paradox). When the wave amplitude is above the threshold, for intermediate values of gamma the presence of a background magnetic field allows for the electric energy dissipation at variance with the behavior of electrostatic wave in unmagnetized plasma, while for high gamma values once again the magnetic field prevents the damping.

Journal Article↗
PubMed2005

Electrostatic interaction of charged planes in the thermal collision plasma: detailed investigation and comparison with experiment.

The spatial distribution of electrostatic potential between the metal planes in a thermal collision plasma at atmospheric pressure has been investigated. It has been shown that the potential requirement must be calculated with respect to the bulk plasma potential, which depends on the ionization equilibrium in the plasma. It has also been shown that the electrostatic perturbation in the plasma is detected only at distances of less than four screening lengths. Long-range perturbation is described by the bulk plasma potential. The electrostatic pressure on the plane as a function of boundary conditions has been found. The experimental results prove the existence of interaction between the planes, located in the low-temperature plasma at a distance that considerably exceeds the screening length, caused by changing the bulk plasma potential. The application of the results to a complex dusty plasma has shown the diminution of-the dust component dissipation in strongly coupled plasmas.

Journal Article↗
PubMed2006

Electrostatic effects in DNA stretching.

The response of a semiflexible polyelectrolyte chain to stretching in the regimes of moderate and weak screening is studied theoretically, with a special focus on DNA experiments. By using the nonlinear Poisson-Boltzmann description of electrostatic self-interactions of the chain, we explicitly demonstrate the applicability of the concept of effective charge to certain aspects of the problem. This charge can be extracted from the far-field asymptotic behavior of the electrostatic potential of the fully aligned chain. Surprisingly, in terms of the effective charge, the electrostatically renormalized persistence length can be formally described by the classical Odijk-Skolnick-Fixman formula, whose domain of applicability is normally limited to the linearized Debye-Hückel (DH) approximation. However, the short-scale behavior of the chain in the nonlinear regime deviates from the of DH-based result, even upon charge renormalization. This difference is revealed in the calculated stretching curves for strongly charged DNA. These results are in good agreement with recent experiments. In the limit of weak screening we predict the elastic response to have a distinctive two-stage character, with a peculiar intermediate "unstretchable" regime.

Computer Simulation↗
PubMed2001

Geometry-dependent electrostatics near contact lines.

Long-ranged electrostatic interactions in electrolytes modify contact angles on charged substrates in a scale and geometry-dependent manner. For angles measured at scales smaller than the typical Debye screening length, the wetting geometry near the contact line must be explicitly considered. Using variational and asymptotic methods, we derive new transcendental equations for the contact angle as functions of the electrostatic potential only at the three phase contact line. Analytic expressions are found in certain limits and compared with predictions for contact angles measured with lower resolution. An estimate for electrostatic contributions to line tension is also given.

Algorithms↗
PubMed2002

Electrostatic field enhancement of Al(111) oxidation.

We show that the electrostatic charging of an aluminum oxide film by electron-bombardment produces a greatly enhanced rate of Al(111) oxidation by O2(g) at 90 K, compared to a film which has not been bombarded by electrons. This novel memory effect for prior electron irradiation is caused by the negative electrostatic potential created and stored on the outer oxide film surface as a result of electron bombardment. The high electrostatic field ( approximately 10(7) V/cm) produced across the depth of the film is postulated to cause an enhancement of ion migration through the film, leading to rapid oxide film growth, as predicted by the Cabrera-Mott theory of low temperature metal oxidation.

Journal Article↗
PubMed2004

Electrostatic shocks excited by velocity modulation of an ion beam in a plasma.

Nonlinear evolutions of electrostatic shocks excited by a velocity-modulated ion beam along a magnetized plasma column are investigated by computer simulation for a Q-machine experiment. In the case of a beam velocity modulation, the perturbations grow spatially with subsequent saturation due to an ion bunching of the beam. With an increase in modulation ratio an electrostatic shock is formed, accompanied with a steepening of the propagating front. In the case of a beam density-modulation, however, the initial density jump decays simply. The velocity modulation method is quite effective for an excitation of electrostatic shocks in the Q-machine plasma with finite Landau damping. The simulation results using velocity modulation are consistent with the experimental results.

Journal Article↗
PubMed2005

In situ discovery of an electrostatic potential, trapping electrons and mediating fast reconnection in the Earth's magnetotail.

Anisotropic electron phase space distributions, f, measured by the Wind spacecraft in a rare crossing of a diffusion region in Earth's far magnetotail (60 Earth radii), are analyzed. We use the measured f to probe the electrostatic and magnetic geometry of the diffusion region. For the first time, the presence of a strong electrostatic potential (1 kV) within the ion diffusion region is revealed. This potential has far reaching implications for the reconnection process; it accounts for the observed acceleration of the unmagnetized ions out of the reconnection region and it causes all thermal electrons be trapped electrostatically. The trapped electron motion implies that the thermal part of the electron distributions are symmetric around v( parallel)=0: f(v( parallel),v( perpendicular)) approximately f(-v( parallel),v( perpendicular)). It follows that the field aligned currents in the diffusion region are limited and fast magnetic reconnection is mediated.

Journal Article↗
PubMed2006

Very high Mach-number electrostatic shocks in collisionless plasmas.

The kinetic theory of collisionless electrostatic shocks resulting from the collision of plasma slabs with different temperatures and densities is presented. The theoretical results are confirmed by self-consistent particle-in-cell simulations, revealing the formation and stable propagation of electrostatic shocks with very high Mach numbers (M>>10), well above the predictions of the classical theories for electrostatic shocks.

Journal Article↗
PubMed2001

The persistence of electrostatically seeded endothelial cells lining a small diameter expanded polytetrafluoroethylene vascular graft.

PURPOSE: The purpose of this study was to evaluate the persistence of electrostatically seeded endothelial cells (ECs) lining an expanded polytetrafluorethylene (e-PTFE) graft after one week exposure to in vivo circulation in a canine femoral artery bypass model. This was accomplished by visualizing the PKH 26 (red fluorescent) label placed in the EC membranes prior to the seeding procedure. Furthermore, this study was performed to confirm that the source of the ECs lining the graft were those from the initial inoculum. METHODS: This evaluation consisted of harvesting autologous, canine jugular vein ECs, PKH 26 labeling of the ECs, electrostatic EC seeding the e-PTFE grafts (4mm GORE-TEX, Length=6cm), implanting the grafts (femoral artery model) for one week, and explanting the grafts for light, fluorescent and scanning electron microscopy evaluations of the luminal surface. RESULTS: The unseeded grafts (controls) had a mean fluorescence surface coverage of 6.82 +/- 7.19%, while the EC seeded grafts had a mean of 90.3 +/- 14.3% which is significantly (p <0.001) different from the controls. Overall, the seeding time including the EC harvesting and PKH 26 labeling protocol was approximately 75 min. CONCLUSIONS: The electrostatically seeded ECs persisted after implantation of the graft as demonstrated by the PKH 26 labeling data. The fluorescent data also demonstrated that the neointima formed (EC luminal surface coverage) one week after implantation was in fact derived from the ECs initially seeded as determined by the abundance of the labeled ECs.

Animals↗