共查询到20条相似文献,搜索用时 31 毫秒
1.
K. V. Safronov D. A. Vikhlyaev A. G. Vladimirov D. S. Gavrilov S. A. Gorokhov A. G. Kakshin E. A. Loboda V. A. Lykov E. S. Mokicheva A. V. Potapov V. A. Pronin V. N. Saprykin P. A. Tolstoukhov O. V. Chefonov M. N. Chizhkov 《Plasma Physics Reports》2010,36(5):443-445
Results of experiments on proton acceleration from aluminum foils and organic films irradiated by laser pulses with intensities of up to 2 × 1019 W/cm2 are presented. To prevent thin targets from destruction by the superluminescence prepulse, a fast light shutter based on a Pockels cell was introduced in the amplifying system of the SOKOL-P facility. As a result, the energy contrast with respect to the superluminescence prepulse increased to 4 × 106, which made it possible to carry out experiments on the irradiation of targets with thicknesses less than 100 nm. It is found that the target material insignificantly affects the yield of accelerated protons. 相似文献
2.
Arnáiz-Cot JJ de Diego AM Hernández-Guijo JM Gandía L García AG 《Biochemical and biophysical research communications》2008,365(3):413-419
The view that Ca2+ entry through voltage-dependent Ca2+ channels (VDCC) and through nicotinic receptors for acetylcholine (nAChRs) causes equal catecholamine release responses in chromaffin cells, was reinvestigated here using new protocols. We have made two-step experiments consisting in an ACh prepulse followed by a depolarizing pulse (DP). In voltage-clamped bovine chromaffin cells an ACh prepulse caused a slow-rate release but augmented 4.5-fold the much faster exocytotic response triggered by a subsequent depolarizing pulse (measured with capacitance and amperometry). If the ACh prepulse was given with mecamylamine or in low external Ca2+, the secretion increase disappeared. This suggests a two-step model for the effects of ACh: (1) meager Ca2+ entry through nAChRs mostly serves to keep loaded with vesicles the secretory machine; and (2) in this manner, the cell is prepared to respond with an explosive secretion of catecholamine upon depolarization and fast high Ca2+ entry through VDCC. 相似文献
3.
Sheri J. Lillard Edward S. Yeung 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1996,687(2):297
A modified version of capillary isoelectric focusing (cIEF) was developed to separate hemoglobin variants contained within single human erythrocytes. Laser-induced native fluorescence with 275 nm excitation was used to detect the separated hemoglobins. In this method, baseline fluctuations were minimized and detection sensitivity was improved by using dilute solutions of anolyte, catholyte, and carrier ampholytes (with methylcellulose). Since electrosmotic flow was used for mobilization of the focused bands, separation and detection were integrated into a single step. The capillary was first filled with only ampholyte solution, and the cell (or standard) was injected as in capillary zone electrophoresis. The ∼90 fl injection volume for individual cells is 7×104 times lower than those previously reported. Adult (normal and elevated A1), sickle (heterozygous), and fetal erythrocytes were analyzed, with the amounts of hemoglobins A0, A1c, S and F determined. The pH gradient for cIEF was linear (r2 = 0.9984), which allowed tentative identification of Hb Fac. Variants differing by as little as 0.025 pI units were resolved. 相似文献
4.
Prepulse inhibition of acoustic startle in aromatase knock-out mice: effects of age and gender 总被引:2,自引:0,他引:2
Estrogen has been suggested to play a neuromodulatory and neuroprotective role on the brain dopamine system. We used aromatase knockout (ArKO) mice that lack a functional aromatase enzyme and are unable to convert testosterone into estrogen, and assessed prepulse inhibition of acoustic startle, locomotor hyperactivity to amphetamine treatment and rotarod performance. Mice were tested at either 1 month, 4–5 months or 12–18 months of age. In male, but not female ArKO mice, there was an age-related reduction of prepulse inhibition. The 12–18 months old male ArKO mice also showed significantly greater amphetamine-induced hyperactivity. Mice heterozygous for the mutation showed no deficits or were in-between wildtype mice and ArKO mice. We postulate that these data indicate a neuroprotective role of estrogen, particularly in male mice, on ageing of brain mechanisms involved in prepulse inhibition and locomotor activity regulation. It is likely that these brain mechanisms are or include dopaminergic activity. 相似文献
5.
Cl− currents (I
Cl) were measured in short fibers (1–2 mm) from the lumbricalis muscle of toads (Bufo arenarum) with two microelectrodes (15°C). Initially the fibers were equilibrated in a high K+-containing solution: (mm) K2SO4 68; Na2SO4 20; KCl 60; CaSO4 8; MgSO4 1; HEPES 2.5. Constant pulses were applied when all the external K+ was replaced by Cs+: Cs2SO4 68; Na2SO4 20; CsCl 60; CaSO4 8; HEPES 2.5 (pH 7.5). Under these conditions about 80–90% of the current is carried by Cl−. The current-voltage relation is almost linear implying constant conductance and hence voltage-independent permeability.
The voltage dependence of the net Cl− current could be fitted by constant field equation with a P
Cl of 3.3 × 10−6 cm/sec. In a separate group of experiments a two-pulse technique was used to estimate the availability and the inactivation
of the initial I
Cl during a test pulse. After returning the potential to the holding potential for various times, test pulses of the same amplitude
and duration of the prepulses were applied. The initial current during the test pulse was 70% of the initial current during
the prepulse and the recovery was complete in less than 300 msec with a linear relationship between the current during the
test pulse and the amplitude of the preceding prepulse. When the test pulses were preceded by a positive prepulse, the initial
current for any given test pulse was larger than with a negative prepulse. If we assumed that the initial current during the
test pulse is a measure of the number of channels open at the end of the prepulse, these results suggest that hyperpolarizing
pulses inactivate and depolarizing prepulses activate the I
Cl.
Received: 31 March 1995/Revised: 27 October 1995 相似文献
6.
Lars H. Wegner 《生物化学与生物物理学报:生物膜》2013,1828(8):1973-1981
Cation selectivity of the cellular membrane of tobacco culture cells (cell line ‘bright yellow-2’) exposed to pulsed electric fields in the millisecond range was investigated. The whole cell configuration of the patch clamp technique was established on protoplasts prepared from these cells. Ion selectivity of the electroporated membrane was investigated by measuring the reversal potential of currents passing through field-induced pores. To this end the membrane was hyper- or depolarized for 10 ms (prepulse); subsequently the voltage was driven to opposite polarity at a constant rate (+ 40 or ? 40 mV/ms, respectively). The experiment was started by polarizing the membrane to moderately negative or positive voltages (prepulse potential ± 150 mV) that would not induce pore formation. Subsequently, an extended voltage range was scanned in the porated state of the membrane (prepulse potential ± 600 mV). IV curves in the porated and the non-porated state (obtained at the same prepulse polarity) were superimposed to determine the voltage at which both curves intersected (‘Intersection potential’). Using a modified version of the Goldmann–Hodgkin–Katz equation relative permeabilities to Ca2 + and various monovalent alkali and organic cations were calculated. Pores were found to be fairly cation selective, with a selectivity sequence determined to be Ca2 + > Li+ > Rb+ ≈ K+ ≈ Na+ > TEA+ ≈ TBA+ > Cl?. Relative permeability to monovalent cations was inversely related to the ionic diameter. By fitting a formalism suggested by Dwyer at al. (J. Gen. Physiol. 75 (1980), 469–492) the effective average diameter of field induced pores was estimated to be about 1.8 nm. Implications of these results for biotechnology and electroporation theory are discussed. 相似文献
7.
V. I. Afonin A. M. Gafarov O. N. Gilev V. I. Ponomarev N. N. Pkhaĭko A. A. Safronov L. N. Shamraev 《Plasma Physics Reports》2007,33(7):562-566
The effect of the direction of a preionization current on the generation of 469-Å X-ray emission from the plasma of a fast capillary discharge in argon was studied experimentally in the SIGNAL facility (the discharge current I = 25–40 kA and the current rise rate dI/dt ~ 1012 A/s). The experiments were performed with 3.1-mm-diameter 157-mm-long ceramic capillaries filled with argon at a pressure of 0.2–1.0 Torr. 相似文献
8.
In this paper we apply a novel JAVA version of a model on the homeostasis of human red blood cells (RBCs) to investigate the changes RBCs experience during single capillary transits. In the companion paper we apply a model extension to investigate the changes in RBC homeostasis over the approximately 200000 capillary transits during the ~120 days lifespan of the cells. These are topics inaccessible to direct experimentation but rendered mature for a computational modelling approach by the large body of recent and early experimental results which robustly constrain the range of parameter values and model outcomes, offering a unique opportunity for an in depth study of the mechanisms involved. Capillary transit times vary between 0.5 and 1.5s during which the red blood cells squeeze and deform in the capillary stream transiently opening stress-gated PIEZO1 channels allowing ion gradient dissipation and creating minuscule quantal changes in RBC ion contents and volume. Widely accepted views, based on the effects of experimental shear stress on human RBCs, suggested that quantal changes generated during capillary transits add up over time to develop the documented changes in RBC density and composition during their long circulatory lifespan, the quantal hypothesis. Applying the new red cell model (RCM) we investigated here the changes in homeostatic variables that may be expected during single capillary transits resulting from transient PIEZO1 channel activation. The predicted quantal volume changes were infinitesimal in magnitude, biphasic in nature, and essentially irreversible within inter-transit periods. A sub-second transient PIEZO1 activation triggered a sharp swelling peak followed by a much slower recovery period towards lower-than-baseline volumes. The peak response was caused by net CaCl2 and fluid gain via PIEZO1 channels driven by the steep electrochemical inward Ca2+ gradient. The ensuing dehydration followed a complex time-course with sequential, but partially overlapping contributions by KCl loss via Ca2+-activated Gardos channels, restorative Ca2+ extrusion by the plasma membrane calcium pump, and chloride efflux by the Jacobs-Steward mechanism. The change in relative cell volume predicted for single capillary transits was around 10−5, an infinitesimal volume change incompatible with a functional role in capillary flow. The biphasic response predicted by the RCM appears to conform to the quantal hypothesis, but whether its cumulative effects could account for the documented changes in density during RBC senescence required an investigation of the effects of myriad transits over the full four months circulatory lifespan of the cells, the subject of the next paper. 相似文献
9.
Computer-assisted morphometry was performed to evaluate the number and cell characteristics of capillary and alveolar leukocytes in rabbit lungs. An image-processing system and a programmable spreadsheet program were used, which allowed morphometric analysis of a large reference area. Neutrophils represented the largest intracapillary leukocyte population (2.2×107/ml parenchyma, which corresponds to an approximately 104-fold microvascular enrichment of this cell type related to cell counts calculated for the capillary blood volume). In addition, large numbers of intracapillary lymphocytes (1.7×107/ml parenchyma; 47-fold enrichment) and monocytes (0.3×107/ml parenchyma; 86-fold enrichment) were detected. The total count of pulmonary leukocytes thus approximated the total number of pulmonary endothelial cells; and the total circulating pools of the different leukocytes were surpassed by the corresponding lung capillary pools, 3.2-fold for neutrophils, 1.2-fold for lymphocytes and 4.8-fold for monocytes. In contrast, alveolar cell numbers ranged from 1–2% of the capillary counts for all types of leukocytes. We conclude that the rabbit lung microvasculature harbours large pools of immunocompetent cells, which may contribute to host-defense mechanisms at the gas-exchange area. 相似文献
10.
During recent years, a renovated interest in the pre-treatment of biomass through torrefaction has led to several proposals on industrial-scale application of the technology. Torrefaction holds promising characteristics for obtaining a high-energy yield biomass for further processing, including densified biofuels such as pellets and briquettes, at low overall costs, low energy input, and high capacity and availability for the near future, having the capability of displacing coal in power facilities. Despite many efforts in developing the technology at an industrial scale, very few manufacturers and companies are offering torrefied machinery and lignocellulosic torrefied biomass. Furthermore, information about the actual profitability of the business, sensitivity, and costs of torrefied biomass are very scarce and are limited to very focused studies in some areas of the production, but not in the overall supply chain, and manufacturing processes. This study aimed to develop and validate a technical and economic model for the production of lignocellulosic torrefied biomass for its utilization in the solid biofuels industry, with a focus on production and delivered costs for U.S. potential manufacturers. This model also includes analysis of important variables affecting production, such as biomass delivered costs, capital expenditure (CAPEX), and technology availability. Results indicate that the production of torrefied lignocellulosic biomass can be profitable for U.S. manufacturers, subject to a high sensitivity on biomass cost, CAPEX, and technology affordability for large-scale production. Other sensitive facts include carbon credits scenarios, which may influence profitability based on analyses of net present value and internal rate of return for the manufacturing facility. 相似文献
11.
V. I. Ostashev A. M. Gafarov V. Yu. Politov A. N. Shushlebin L. V. Antonova O. N. Gilev A. A. Safronov A. V. Komissarov 《Plasma Physics Reports》2006,32(6):489-499
Results are presented from time-resolved measurements of the soft X-ray emission in the 10-to 40-eV spectral range from the plasma of a pulsed capillary discharge in argon at current pulse amplitudes of up to 26 kA and a current rise time of ~1012 A/s. The experiments were carried out with 0.3-cm-diameter 15.7-cm-long ceramic capillaries filled with argon at a pressure of 0.25–0.5 Torr in the SIGNAL electrophysical facility. The experimental data are interpreted via computer simulations of the magnetohydrodynamics and level-by-level ion kinetics of an argon plasma. The results obtained indicate that soft X-ray laser pulses with a photon energy of 26.4 eV and duration of 1–2 ns are generated ≈33 ns after the beginning of the discharge current pulse. 相似文献
12.
K. A. Ivanov D. S. Uryupina N. Morshedian R. V. Volkov A. B. Savel’ev 《Plasma Physics Reports》2010,36(2):99-104
Results are presented from experimental studies of ion acceleration under the action of femtosecond laser pulses with an intensity
of 1017 W/cm2, incident onto the free surfaces of melted gallium and indium. The effect of the polarization direction of a linearly polarized
laser pulse and the amplitude of a short prepulse, which precedes the main pulse by several nanoseconds, on the parameters
of accelerated ions is investigated. It is found that, even for such a moderate laser intensity, the characteristic velocity
of fast ions ejected along the reflected beam is a factor of 1.5 higher than that of ions ejected along the normal to the
target surface. It is shown that, as the prepulse energy increases, the hard X-ray yield and the mean energy of hot electrons
increase substantially, whereas the velocity of both fast and slow ions decreases appreciably regard-less of laser polarization. 相似文献
13.
Background
Prepulse inhibition (PPI) depicts the effects of a weak sound preceding strong acoustic stimulus on acoustic startle response (ASR). Previous studies suggest that PPI is influenced by physical parameters of prepulse sound such as intensity and preceding time. The present study characterizes the impact of prepulse tone frequency on PPI.Methods
Seven female C57BL mice were used in the present study. ASR was induced by a 100 dB SPL white noise burst. After assessing the effect of background sounds (white noise and pure tones) on ASR, PPI was tested by using prepulse pure tones with the background tone of either 10 or 18 kHz. The inhibitory effect was assessed by measuring and analyzing the changes in the first peak-to-peak magnitude, root mean square value, duration and latency of the ASR as the function of frequency difference between prepulse and background tones.Results
Our data showed that ASR magnitude with pure tone background varied with tone frequency and was smaller than that with white noise background. Prepulse tone systematically reduced ASR as the function of the difference in frequency between prepulse and background tone. The 0.5 kHz difference appeared to be a prerequisite for inducing substantial ASR inhibition. The frequency dependence of PPI was similar under either a 10 or 18 kHz background tone.Conclusion
PPI is sensitive to frequency information of the prepulse sound. However, the critical factor is not tone frequency itself, but the frequency difference between the prepulse and background tones. 相似文献14.
Takahashi M Kakita A Futamura T Watanabe Y Mizuno M Sakimura K Castren E Nabeshima T Someya T Nawa H 《Journal of neurochemistry》2006,99(3):770-780
Brain-derived neurotrophic factor (BDNF) is involved in synaptic development and plasticity, and alterations in BDNF expression or signaling are implicated in drug addiction and psychiatric diseases, such as depression and schizophrenia. In this study, we administered phencyclidine to postnatal and adult rats with different time schedules, and determined the correlations between BDNF expression and the behavioral effects. Both single and repeated phencyclidine injections into adult rats induced BDNF up-regulation in the corticolimbic system and a decrease in prepulse inhibition, both of which were transient. In contrast, subchronic postnatal administration increased BDNF protein and mRNA levels in the hippocampus and entorhinal cortex, which were sustained until 8 weeks of age. In parallel, the postnatal rats treated with phencyclidine developed a persistent decrease in prepulse inhibition at the adult stage. The chronic BDNF increase appeared to contribute to the prepulse inhibition abnormality, as subchronic BDNF infusion into the hippocampus of normal rats mimicked the prepulse inhibition deficits. This study suggests that phencyclidine exposure during brain development induces sustained BDNF up-regulation in the limbic system with a biological link to sensorimotor gating deficits. 相似文献
15.
Michael Meyring Dirk Strickmann Bezhan Chankvetadze Gottfried Blaschke Claudia Desiderio Salvatore Fanali 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1999,723(1-2)
High-performance liquid chromatography (HPLC), nano-HPLC, capillary electrochromatography (CEC) and on-line HPLC–atmospheric pressure chemical ionization mass spectrometry (APCI-MS) techniques were used for the identification and detailed characterization of two new metabolites of the former sedative drug thalidomide (TD). The advantages of nano-HPLC and CEC are higher peak efficiency and a drastic decrease in the analysis time, which, together with lower sample dilution during the analyses, allowed to obtain a detection sensitivity that was comparable to HPLC with common-sized columns. Both, nano-HPLC and CEC could be realized in the commercially available capillary electrophoresis system HP3D. On-line HPLC–APCI-MS coupling is a very useful technique for the rapid identification of metabolites without any need for reference compounds. 相似文献
16.
Chen Li Tatsuhito Nishiguchi Kyoko Shinzawa-Itoh Shinya Yoshikawa Takashi Ogura Satoru Nakashima 《BBA》2018,1859(10):1045-1050
Time-resolved IR analyses for the protonation and polarity changes of carboxyl groups involved in proton pump enzymes under turnover conditions are indispensable for elucidation of their proton-pump mechanisms. We have developed a new time-resolved infrared facility by introducing a flow system for transferring highly concentrated and thus viscous protein solution to a thin (50?μm) flow cell equipped in a highly sensitive IR spectrometer constructed with the femtosecond mid-IR pulse laser with spectral width of 350?cm?1 as an IR white light source equipped with multi-channel MCT detector. This facility equipped with O2 supply system enables the sub-millisecond time scale infrared measurements of the O2 reduction coupled with proton pumping by bovine cytochrome c oxidase (CcO) initiated by CO-flash photolysis in the COOH (1725–1770?cm?1) region with the accuracy of about 10?μO.D. under the background O.D. of 1. The facility identifies a band intensity change at ~1744?cm?1 assignable to protonation of a carboxyl group coupled with a single electron transfer to the O2 reduction center within 1?ms after initiation of the reaction. The results suggest that the facility detects protonation of a single carboxyl group included in large proteins like as CcO (210?kDa). The present facility sensitively identifies also polarity changes in COOH group by detecting shifts of the bands near 1750?cm?1 and 1760?cm?1, without significant intensity changes. These findings show the performance of this facility sufficiently high for providing crucial information for understanding the proton transferring mechanisms of protein carboxyl groups. 相似文献
17.
《Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)》2016,32(12):1862-1871
In this work, we used the Monte Carlo-based Geant4 simulation toolkit to calculate the ambient dose equivalents due to the secondary neutron field produced in a new projected proton therapy facility. In particular the facility geometry was modeled in Geant4 based on the CAD design. Proton beams were originated with an energy of 250 MeV in the gantry rooms with different angles with respect to the patient; a fixed 250 MeV proton beam was also modeled. The ambient dose equivalent was calculated in several locations of interest inside and outside the facility, for different scenarios. The simulation results were compared qualitatively to previous work on an existing facility bearing some similarities with the design under study, showing that the ambient dose equivalent ranges obtained are reasonable. The ambient dose equivalents, calculated by means of the Geant4 simulation, were compared to the Australian regulatory limits and showed that the new facility will not pose health risks for the public or staff, with a maximum equivalent dose rate equal to 7.9 mSv/y in the control rooms and maze exit areas and 1.3·10−1 mSv/y close to the walls, outside the facility, under very conservative assumptions. This work represents the first neutron shielding verification analysis of a new projected proton therapy facility and, as such, it may serve as a new source of comparison and validation for the international community, besides confirming the viability of the project from a radioprotection point of view. 相似文献
18.
Mobilization of aluminium in the rhizosphere soil solution of growing tree roots in an acidic soil 总被引:2,自引:0,他引:2
Chemical conditions in the rhizosphere in many respects are different from the bulk soil. Especially in acid forest soils
aluminium chemistry at the soil root interface is of particular interest because of its importance for evaluating the risk
of rhizotoxicity. In the present study we have used micro suction cups to collect soil solution from the rhizosphere of oak
seedlings (Quercus robur L.) in high spatial resolution and capillary electrophoresis for the determination of major ions
and Al3+. While the concentrations of nutrient cations, especially Ca2+ and Mg2+, decreased in the vicinity of growing roots the concentrations of Al3+ significantly increased. Al3+-ions were probably released when root-exuded protons were buffered by the soil. Their occurrence indicates, that the oak
roots in our experiments had only limited capabilities to detoxify Al in their rhizosphere. The restriction of this effect
to the very small soil compartment close to the roots suggests, that common soil analysis which neglect rhizosphere processes
might greatly underestimate the in situ concentration of Al3+ near tree roots. Our experiments furthermore indicate, that also suberized roots have a significant influence on rhizosphere
soil solution chemistry.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
19.
The optimum number of total capillaries in the whole human body was estimated from the analysis of the efficiency for oxygen
(O2) transport in the vascular-tissue system. We used a tissue model composed of uniform spheres in which O2 diffuses from the capillary located at the centre of each sphere towards the surrounding tissue consuming O2 at a constant rate. The tissue mass supplied by a single capillary was estimated as the area of positive O2 concentration under a given condition of capillary flow and O2 consumption rate. Total tissue mass was determined as the function of the capillary numbern and the total blood flow. On the other hand, the energy cost required to maintain the vascular system withn terminals was assessed by using the minimum volume model (Kamiya and Togawa,Bull. math. Biophys.
34, 431–438, 1972). The efficiency of the entire vascular-tissue system was evaluated by calculating the ratio of total tissue
mass/cost function. The result of the calculation using physiological data of cardiac output and O2 consumption for an average human adult during a heavy exercise revealed the maximum efficiency occurring at the capillary
number 3.7×1010 which coincided well with its normal range of physiological estimates (3.2×1010–4.2×1010). We concluded that the entire vascular-tissue system is constructed so as to attain the highest efficiency in O2 transport at its maximum activity. 相似文献
20.
Large-volume sample stacking of selected drugs of forensic significance by capillary electrophoresis
《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1996,681(1):125-131
Large-volume sample stacking capillary electrophoresis (LVSS-CE) and conventional capillary electrophoresis (CE) are compared for the separation of drugs of significance to forensic and clinical analyses. LVSS-CE for cations requires the use of an electroosmotic flow (EOF) modifier in conjunction with polarity switching to effect on-column concentration of an analyte and its subsequent migration in the capillary. The run buffer consists of 0.05 mol dm−3 disodium tetraborate adjusted to pH 2.2 with orthophosphoric acid, and the EOF modifier is 0.002 mol dm−3 cetyltrimethylammonium bromide. CE investigations used an identical run buffer minus the EOF modifier. LVSS-CE and CE investigations used injection times of 30 s and 3 s, respectively. Both modes of capillary electrophoresis are compared in terms of their limits of detection, efficiency, resolution and reproducibility. LVSS-CE is also applied to the analysis of a spiked urine sample. 相似文献