Search

The magnetic and compressive properties of the ternary Ni40.6Fe36.4Ti23 eutectic alloys solidified under electromagnetic levitation condition were investigated. An undercooling range from 32 to 141 K was achieved, and a ternary eutectic consisting of a fibrous Fe2Ti phase and lamellar γ-Fe(Ni) + Ni3Ti phases formed. In the ternary eutectic, the γ-Fe(Ni) and Ni3Ti phases kept cooperative growth, while the Fe2Ti phase grew either cooperatively with these two phases or sometimes independently. Theoretical calculations showed that there existed a vertical flow field and temperature gradient in the center of the levitated alloy droplet, contributing to the directional growth behavior of eutectic grain. The growth velocity of primary Ni3Ti dendrite increased by 2.4 times, while that of ternary eutectic increased by 77% as undercooling rose, and consequently, the microstructures were significantly refined. The temperature stability of coercivity and residual magnetization below ambient temperature was improved once alloy undercooling reached 128 K, ascribed to the enhancement of the exchange coupling effect between the magnetic domains inside refined grains. The fracture strain of the ternary eutectic alloy increased with undercooling because microcrack propagation was further hindered and the plastic deformation was more homogeneous. Meanwhile, the fracture was dominated by transgranular (TG) mode at an undercooling of 132 K because the bonding force of grain boundaries became stronger.

To study the mechanism of brake squeal of light-rail trains, a field test and a simulation analysis of disc brake squeal were carried out. In the field test measurement, the noise and vibration cha...

This article studies a special rail corrugation phenomenon occurring at a braking section of Shenzhen Metro Line 3 based on friction-excited oscillation. The rail corrugation is strongly re...

Rail corrugation is a problem that have perplexed the researchers and administrators in railway engineering for many decades with complex formation mechanism and various affecting factors. In this paper, two finite element models includes the track system and the wheelset with an inner axlebox type bogie and with an outer axlebox type bogie are established to analyze the stability of the system using the complex modal analysis. The multibody dynamic analysis of the vehicle-track system is conducted to determine the relevant parameters that are the foundation of the finite element analysis. The effect of the axlebox arrangement of the bogie, the damping and stiffness of primary spring, the lateral spacing between the primary suspension points and the weight of the bogie and the carbody on corrugation are investigated. The results show: the inner axlebox type bogie is favorable for suppressing the rail corrugation. When the lateral spacing between the primary suspension points is 0.86 m, the effect to suppress the rail corrugation is best. The higher the vertical stiffness of the primary spring, the more easily the rail corrugation occurs. Too high or too low vertical damping of the primary spring can easily cause rail corrugation. The heavier the vehicle and the bogie, the greater the possibility of the rail corrugation occurrence.

In the paper, the frictional self-excited vibration of a wheelset-track system caused by the saturated wheel-rail creep force is proposed as a possible mechanism for wheel polygonal wear of high-speed trains. The wheelset-track system model is established, which consists of a wheelset, two rails, some sleepers and a slab. The stability of the wheelset-track system is studied through the complex eigenvalue method. Results show that the unstable vibration frequency of the wheelset-track system is f= 495.01 Hz, which can lead to the 18th-order wheel polygonal wear. This simulation result is approximately consistent with the field measurement result. Furthermore, the parameters sensitivity analysis shows that increasing the vertical damping of the fastener to a certain extent can suppress or eliminate wheel polygonal wear. In addition, a transient dynamic analysis of the wheelset-track system with the wheelset eccentricity is conducted. Results indicate that the wheelset eccentricity is an important factor affecting wheel polygonal wear.

Spectral similarity indices were used to select similar soil samples from a spectral library and improve the predictive accuracy of target samples. There are many similarity indices available, and precisely how to select the optimum index has become a critical question. Five similarity indices were evaluated: Spectral angle mapper (SAM), Euclidean distance (ED), Mahalanobis distance (MD), SAM_pca and ED_pca in the space of principal components applied to a global soil spectral library. The accordance between spectral and compositional similarity was used to select the optimum index. Then the optimum index was evaluated if it can maintain the greatest predictive accuracy when selecting similar samples from a spectral library for the prediction of a target sample using a partial least squares regression (PLSR) model. The evaluated physiochemical properties were: soil organic carbon, pH, cation exchange capacity (CEC), clay, silt, and sand content. SAM and SAM_pca selected samples were closer in composition compared to the target samples. Based on similar samples selected using these two indices, PLSR models achieved the highest predictive accuracy for all soil properties, save for CEC. This validates the hypothesis that the accordance information between spectral and compositional similarity can help select the appropriate similarity index when selecting similar samples from a spectral library for prediction.

In a field test, three corrugation profiles of rails and their corresponding vibrations were measured, and the wavelengths and frequencies of rail corrugations were obtained. In the model prediction, finite-element models of the self-excited vibrations corresponding to three different wheelset–track systems were established. The corrugation frequencies of these models were predicted, and a comparison between the measured and the predicted corrugation frequencies showed that they are in good agreement. It can be concluded that the self-excited vibration of a wheelset–track system can cause rail corrugation. A benchmark condition for the validation of rail corrugation models is proposed.

The reaction of Cu(NO3)2 · 3H2O with rigid ligand 4'-(1H-tetrazol-5-yl)-[1,1'-biphenyl]-3,5-dicarboxylic acid (H3L) gave a new metal-organic framework of [Cu2(μ3-OH)(L)(H2O)2] n (I) (CIF file CCDC no. 1533273). Complex I has a truncated cuboctahedra that was connected by trigonal Cu3O(N4CR)3 trimers using each tetrazolate (N4CR) moiety and shows a overall 3D nnt net with (6.82)6(83)2(62.84)3 topology. The properties of gas adsorption and the degradation of the methyl violet have been examined.

The longitudinal spin Seebeck effect (LSSE) with a vertical temperature gradient is one of the most important mechanisms to generate pure spin current. Previous studies of the LSSE excited spin current focus mainly on the magnetic insulators, a little on ferromagnetic metals, and rarely on ferromagnetic half metals. In this work, we demonstrate a significant spin current injected from the highly spin polarized ferromagnetic half metal $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ by the LSSE. The sign of the thermal voltage can be reversed by using the spin current detector Cr with a large negative spin Hall angle. The ratio of the inverse spin Hall voltage to the total thermal signal in $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ is much larger than that in ferromagnetic metals, such as permalloy and CoFeB. The nontrivial temperature-dependent voltage suggests that the thermal transport in $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ is carried by magnons. This study provides insight into the mechanism of thermally excited spin current in ferromagnetic half metals and recommends the highly spin polarized $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ as a promising candidate for metal-based spin caloritronics devices.

Some research on the in-situ radioactivity measurement in seawater and development of underwater spectrometer using NaI(Tl) scintillation crystal are being carried out for the automatic and continuous monitoring in the marine environment. The gamma spectrometer must be efficiency calibrated for the detection of radionuclides in the seawater. For the problem of traditional experiments, a simulation model of in-situ radioactivity measurement in the seawater was established by using Monte Carlo statistical method. The model simulates the in-situ measurement environment of seawater and the characteristics of the underwater spectrometer developed by ourselves. By calculating the interaction between gamma-ray photons emitted by radionuclides in seawater and various atoms in seawater and the internal structures of the spectrometer, the marine detection efficiency of the underwater spectrometer developed was calculated and verified by the field experiments. The results show that this kind of non-experimental calibration method is effective and feasible for the underwater spectrometer and further research and experiments will continue.

The design, synthesis, and crystallographic analysis of protein-inhibitor complexes is described for a novel series of nonpeptidic HIV protease (HIV Pr)inhibitors. Beginning with a cocrystal structure of a Phe-Pro peptidomimetic bound to the HIV Pr, design was initiated that resulted in the substituted 2-butanol compound 8 as the lead compound (Ki = 24.5 microM, racemic mixture). Modifications on the initial compound were then made on the basis of its cocrystal structure with HIV Pr and inhibition data, resulting in compounds with enhanced potency against the enzyme (compound 18, Ki = 0.48 microM). These inhibitors were found to bind to the enzyme essentially as predicted on the basis of the original design hypothesis. Stereospecific synthesis of individual enantiomers confirmed the prediction of a binding preference for the S alcohol stereochemistry. Modest antiviral activity was demonstrated for several of the more potent HIV Pr inhibitors in a HIV-1 infected CEM-SS cell line.

The cocrystal structures of LY289612 and LY297135 were used as a starting point in the design of nonpeptidic HIV-1 protease inhibitors. This report details the discovery of a series of novel aromatic P 2 replacement groups. The 3-hydroxy-2-methyl benzoic acid group, discovered in AG1254, was incorporated into the hydroxyethyl amine series to produce the potent antiviral compound (LY309391/ AG1310).

The X-ray crystal-structure-based design, synthesis, computational evaluation, and activity of a novel class of HIV protease inhibitors are described. The initial lead compounds 2 and 3 were designed by modeling replacement groups for the C-terminal Val-Val-OCH3 of a known hydroxyethylene inhibitor into the active site of the reported crystal structure of HIV protease complexed with MVT-101. The lead compound 2 was found to be a modest inhibitor with a Ki = 1.67 microM. The X-ray crystal structure of compound 2 complexed with HIV protease was solved and used for subsequent design. The lead compound 3 was found to be a more potent inhibitor with Ki = 0.2 microM, and the structure of it complexed with HIV protease was also solved and used for subsequent design. Modification of both the C-terminus and N-terminus of indole 3 resulted in compounds with Ki = 30 nM. Using the crystal structure of compounds 2 and 3 with HIV protease as a starting point, the thermodynamic cycle perturbation molecular dynamics method was applied to a select group of compounds in order to test the accuracy of this type of computation within a series of closely related compounds.

The design, synthesis, and crystallographic analysis of protein−inhibitor complexes is described for a novel series of nonpeptidic HIV protease (HIV Pr) inhibitors. Beginning with a cocrystal structure of a Phe-Pro peptidomimetic bound to the HIV Pr, design was initiated that resulted in the substituted 2-butanol compound 8 as the lead compound (Ki = 24.5 μM, racemic mixture). Modifications on the initial compound were then made on the basis of its cocrystal structure with HIV Pr and inhibition data, resulting in compounds with enhanced potency against the enzyme (compound 18, Ki = 0.48 μM). These inhibitors were found to bind to the enzyme essentially as predicted on the basis of the original design hypothesis. Stereospecific synthesis of individual enantiomers confirmed the prediction of a binding preference for the S alcohol stereochemistry. Modest antiviral activity was demonstrated for several of the more potent HIV Pr inhibitors in a HIV-1 infected CEM-SS cell line.

Effects of myocardial hypertrophy on the Na+/Ca2+ exchange current in isolated rat cardiac myocytes were investigated, using whole cell patch techniques. Goldblatt 2-kidney, one-clip technique was used to induce cardiomyocyte hypertrophy. The results demonstrated that the Ni(2+)-sensitive Na+/Ca2+ exchange current density was larger in hypertrophied cells than that in normal cells. At a holding potential of mV, the outward current densities were 1.53 +/- 0.31 pA/pF in normal cells and 2.62 +/- 0.53 pA/pF in hypertrophied cells (P0.01). At a holding potential of -100 mV, the inward current densities were 0.42 +/- 0.14 pA/pF in normal cells and 1.12 +/- 0.33 pA/pF in hypertrophied cells (P0.001). The results suggest that during myocardial hypertrophy the Na+/Ca2+ exchange current is significantly increased.

To study the effects of E-4031 on the Na+/Ca2+ exchange currents (INa/Ca).The quasi-steady state current-voltage relationship from the isolated rat ventricular myocytes was measured using whole-cell voltage-clamp techniques with a ramp pulse protocol.At potential of mV, E-4031 5, 10, and 20 mumol.L-1 increased Ni(2+)-sensitive current from (0.48 +/- 0.12), to (0.78 +/- 0.20), (0.96 +/- 0.16), and (1.15 +/- 0.13) pA/pF, respectively; tetradecanoylphorbol acetate (TPA) 50 nmol.L-1 increased Ni(2+)-sensitive current from (0.60 +/- 0.16) to (1.33 +/- 0.25) pA/pF. Tamoxifen 20 mumol.L-1 completely prevented the current changes induced by E-4031 and TPA.E-4031 stimulates the Na+/Ca2+ exchange via a protein kinase C-dependent pathway.

To study the effects of propylbutyldopamine (PBDA) on the inward rectifier potassium current (Ik1).The quasi-steady state current-voltage relationship from the isolated guinea pig ventricular cells were measured using whole-cell patch-clamp techniques with a slow ramp depolarization (8 mV.s-1).PBDA 5, 50, and 100 mumol.L-1 concentration-dependently reduced the inward rectifier potassium current. PBDA blocked Ik1 in guinea pig ventricular cells. The effect of PBDA was not blocked by the selective dopamine D2-receptor blocker, domperidone.PBDA inhibited Ik1 directly, independent of the dopamine D2-receptor.

To study the effects of norepinephrine (NE) and isopentenyladenosine (Iso) on Na+/Ca2+ exchange currents and the receptor mechanism.The quasi-steady state current-voltage relationship from the isolated guinea pig ventricular myocytes was measured using whole-cell voltage-clamp techniques with a ramp pulse protocol.At potential of +50 mV, NE 0.005, 0.05, and 5 mumol.L-1 increased the Ni(2+)-sensitive current by 29% +/- 9%, 72% +/- 11%, and 124% +/- 31.4%, respectively; Iso 1.5, 150, and 1500 nmol.L-1 caused increases in the Ni(2+)-sensitive current by 2.8% +/- 2.8%, 56% +/- 13%, and 102% +/- 12%, respectively. Propranolol 10 mumol.L-1 completely inhibited the current changes induced by NE and Iso while phentolamine 50 mumol.L-1 showed no effects.NE and Iso increased the Na+/Ca2+ exchange currents via stimulation of cardiac beta-adrenoceptor.

To study the effect of phentolamine on L-type calcium currents (ICa) and ATP-sensitive K+ currents (IK,ATP) in ventricular myocytes.ICa and IK,ATP were observed using patch clamp techniques in whole-cell recording configuration.Phentolamine reduced ICa of ventricular myocytes in concentration-dependent and voltage-independent manners. Phentolamine 5, 25, and 100 mumol.L-1 decreased ICa from 370 +/- 99 nA to 310 +/- 95 nA (17% block, n = 6, P0.01), from 230 +/- 98 nA to 180 +/- 73 nA (23% block, n = 5, P0.05), and from 293 +/- 66 nA to 206 +/- 44 nA (30% block, n = 5, P0.01), respectively, without affecting the current-voltage relationship. Prazosin 100 mumol.L-1 and yohimbine 100 mumol.L-1, which were specific blockers of alpha 1 and alpha 2 adrenoceptors respectively, did not show the inhibitory effect on ICa. Phentolamine 100 mumol.L-1 also inhibited the IK,ATP induced by 2, 4-dinitrophenol (DNP) at 0 mV from 3.2 +/- 0.6 nA to 0.8 +/- 0.5 nA (75% block, n = 4, P0.01).Phentolamine directly inhibits ICa and IK,ATP in guinea pig ventricular myocytes.

A series of potent nonpeptide inhibitors of the HIV protease have been identified. Using the structure of compound 3 bound to the HIV protease, bis tertiary amide inhibitor 9 was designed and prepared. Compound 9 was found to be about 17 times more potent than 3, and the structure of the protein-ligand complex of 9 revealed the inhibitor binds in an inverted binding mode relative to 3. Examination of the protein-ligand complex of 9 suggested several modifications in the P1 and P1' pockets. Through these modifications it was possible to improve the activity of the inhibitors another 100-fold, highlighting the utility of crystallographic feedback in inhibitor design. These compounds were found to have good antiviral activity in cell culture, were selective for the HIV protease, and were orally available in three animal models.

The mechanisms responsible for the cardiac positive inotropic effects of dopexamine hydrochloride, a combined dopamine receptor agonist at both D1-receptors and beta 2-adrenoceptors, were studied. The calcium channel currents were recorded using whole-cell patch clamp technique in isolated guinea pig ventricular myocytes. At a holding potential of -40 mV, cells were depolarized to 0 mV for 400 ms at a frequency of 0.2 Hz. Dopexamine hydrochloride at doses of 5, 50 and 100 microM increased the verapamil-sensitive Ca2+ inward current by 109, 147 and 194%, respectively. The effects of dopexamine hydrochloride on Ca2+ current reached its maximum at 5 min and partially recovered after washout of the drugs. The increased Ca2+ current induced by dopexamine hydrochloride was completely inhibited by 20 microM propranolol, a beta-adrenoceptor antagonist, and was not antagonized by 20 microM of SCH23390, a highly selective D1-receptor antagonist. These results suggest that the cardiac positive inotropic effects of dopexamine hydrochloride are brought about by the increase of Ca2+ current via stimulation of beta 2-adrenoceptors.

The effects of anti-peptide antibodies (Ab) against the second extracellular loop of human muscarinic receptor-2 on cardiac function in rats in vivo were studied. These effects were compared with those of the muscarinic receptor agonist, carbachol (Carb). It was shown that: (1) both Carb and Ab administered intravenously in the same doses of 0.4 nmol, 1.0 nmol, and 2.0 nmol were able to inhibit the maximal rate of rise of ventricular pressure (+dp/dt max) in a dose-dependent manner. (2) The isoproterenol (Iso)-induced increase in HR and +dp/dt max were also markedly inhibited by Carb and Ab. Administration of 1.0 nmol Carb decreased the Iso-stimulated increase of HR from 13.6 +/- 2.0 to 4.9 +/- 0.7% and decreased the increase of +dp/dt max from 27.9 +/- 3.2 to 4.8 +/- 0.6%, respectively; whereas Ab decreased the HR to 6.5 +/- 1.1% and +dp/dt max to 13.5 +/- 1.2%, respectively. (3) Both the inhibitory effects of Carb and Ab could be significantly blocked by atropine (1.4 nmol). These findings suggest that the Ab display a stimulatory muscarinic activity similar to Carb in inhibiting the cardiac function as evidenced by its negative chronotropic and inotropic effects.

In whole cell voltage clamp experiment with isolated guinea pig ventricular myocytes, tocainide was shown to exhibit a concentration-dependent inhibition of calcium current (ICa) and delayed rectifier potassium current (IK). Tocainide with a therapeutic concentration of 50 mumol.L-1 significantly inhibited the ICa and Itail (deactivating tail current of IK) by 16% and 3% respectively. Inhibition of ICa by tocainide was also shown to be dependent upon stimulating frequencies, with a greater blockade occurring at 2.0 Hz (57%) than at 0.2 Hz (17%). Tocainide was found to inhibit the IK,ATP by 74% at 200 mumol.L-1 but not at 50 mumol.L-1. These inhibitory effects on ICa and IK can probably explain the therapeutic effect of tocainide on supraventricular tachycardia, and the shortening of plateau phase of action potential.

The effects of dopexamine (DPX), a new dopamine receptor agonist, on transmembrane potential and effective refractory period (ERP) of isolated guinea pig ventricular muscle superfused either with hypoxia or mimic ischemia perfusates were investigated by using intracellular microelectrode technique and compared with fenoldopam (FODA) and procaterol. DPX (3 x 10(-6) mol.L-1) was found to significantly reduce both the extent of decrease of resting potential, action potential amplitude and maximal upstroke velocity and the degree of shortening of action potential duration caused by hypoxia or ischemia. These effects of DPX were significantly greater than those of FODA and procaterol albeit the latter showed effects similar to DPX. DPX could not only lengthen the abbreviated ERP resulting from hypoxia, but also shorten the prolonged ERP caused by ischemia. This action of DPX was more evident than that of FODA and procaterol. The results reveal the potential advantages of DPX over other dopaminergic agonists in the antiarrhythmic activity during myocardial ischemia.

Film stacks of a-SiC:H and molecularly templated nanoporous silica thin films have been prepared, and alkylation of pore surfaces of the nanoporous silica layer by the a-SiC:H layer was studied. The a-SiC:H thin films were deposited by high-density plasma chemical vapor deposition (HDP-CVD) using trimethylsilane (3MS) as the precursor. Carbon is found to uniformly distribute in the thin nanoporous silica film, and the carbon content in the nanoporous film decreases with increasing the a-SiC:H deposition temperature. We used the modified Sanderson formalism to estimate the corresponding Si(2p) and C(1s) electron energies in x-ray photoelectron spectra (XPS) for possible terminal species on pore surfaces in the nanoporous silica layer. According to the XPS analysis and thermal desorption mass spectroscopy, the terminal species are probably in the chemical form of alkoxyl structures. The alkoxyl terminal groups introduced into the nanoporous silica thin film are believed to stem from hydrocarbons trapped in ...

Microstructural and mechanical properties of organic surfactant templated nanoporous thin silica films have heen studied by X-ra diffraction. Fourier transform infrared spectroscopy, and nanoindentation. Compared with many other porous low-k dielectrics, th self-assembled molecularly templated nanoporous silica films demonstrate better mechanical properties. This is ascribed to th presence of a well-ordered pore channel structure in the nanoporous silica thin films. Hardness and elastic modulus arc strongl dependent on film preparation and modification methods. Trimethylsilylation by hexamethylsilazane vapor treatment effectivel enhances the mechanical strength of the nanoporous silica films. When the sol precursor solution is mixed with trimethylchl rosilane (TMCS), the resulting nanoporous films have a weaker mechanical strength. The pore channel structure of the nanoporo silica film becomes less ordered for the TMCS derivatized nanoporous films. In addition. the chemical structure in the silica soli matrix of the TMCS derivatized films is more disordered than those without TMCS modification. The nanoindentation measure ment results are discussed in terms of the pore microstructure of the nanoporous silica network and the springback effect due 1 the presence of trimethylsilyl groups in the nanopores.

Scanning capacitance microscopy ~SCM! is employed to examine iron-contaminated p-type Si samples. For slightly contaminated samples, a dc voltage of 20.8 V, applied between the sample and the conductive tip, induces positive trapped charges. Owing to the existence of these charges, the region containing trapped charges exhibits an obviously low dC/dV signal. According to contact-mode atomic force microscopy results, the surface morphology has little effect on the SCM signal. The experimental results indicate that SCM is capable of detecting the distribution of oxidation-related defects which cannot otherwise be easily observed by atomic force microscopy and transmission electron microscopy. © 2001 The Electrochemical Society. @DOI: 10.1149/1.1389877# All rights reserved.

The effects of arginine aspirin (AAs) on the effective refractory period (ERP) and ventricular fibrillation threshold (VFT) of ischemic ventricular muscle were observed in 24 anesthetized open-chest rabbits. that the platelet aggregation rate was shown to be increased by 11 +/- 5%, and VFT decreased by 24 +/- 3 mA at 50 min after coronary occlusion. Compared with values at 10 min postocclusion, ERP of ventricular muscle in border ischemic zone (BIZ) and central ischemic zone (CIZ) was shortened by 20 +/- 10% and prolonged by 35 +/- 22 ms, respectively, and dispersions of ERP between CIZ and BIZ were increased by 52 +/- 17 ms, compared with control values, (p less than 0.01). By giving an intravenous injection of AAs at 0.5 h before coronary occlusion, changes in parameters as mentioned above were obviously relieved as compared with the same parameters in the group of simple coronary occlusion at 50 min postocclusion, (p less than 0.01). These results suggest that AAs may inhibit platelet aggregation, reduce dispersions of ERP and elevate VFT after coronary occlusion.

Electron paramagnetic resonance (EPR) measurements were performed on photosystem II (PSII) membranes that were treated with 2 M NaCl to release the 17- and 23-kilodalton (kDa) polypeptides. By using 75 microM 3-(3,4-dichlorophenyl)-1,1-dimethylurea to limit the photosystem II samples to one stable charge separation in the temperature range of 77-273 K, we have quantitated the EPR signals of the several electron donors and acceptors of photosystem II. It was found that removal of the 17- and 23-kDa polypeptides caused low potential cytochrome b559 to become fully oxidized during the course of dark adaptation. Following illumination at 77-130 K, one chlorophyll molecule per reaction center was oxidized. Between 130 and 200 K, both a chlorophyll molecule and the S1 state were photooxidized and, together, accounted for one oxidation per reaction center. Above 200 K, the chlorophyll radical was unstable. Oxidation of the S1 state gave rise to the S2-state multiline EPR signal, which arises from the Mn site of the O2-evolving center. The yield of the S2-state multiline EPR signal in NaCl-washed PSII membranes was as high as 93% of the control, untreated PSII membranes, provided that both Ca2+ and Cl- were bound. Furthermore, the 55Mn nuclear hyperfine structure of the S2-state multiline EPR signal was unaltered upon depletion of the 17- and 23-kDa polypeptides. In NaCl-washed PSII samples where Ca2+ and/or Cl- were removed, however, the intensity of the S2-state multiline EPR signal decreased in parallel with the fraction of PSII lacking bound Ca2+ and Cl-.(ABSTRACT TRUNCATED AT 250 WORDS)

A highly purified RNA polymerase preparation from pea chloroplasts has been shown to specifically transcribe the 16S rRNA gene in vitro using the recombinant pCB2-8 DNA as a template. The RNA polymerase has been found to show maximum activity and specificity with pea supercoiled rDNA as a template. At low concentrations of ribonucleoside triphosphates, the RNA polymerase selectively initiates transcription on the 16S rRNA gene. A part of the 16S rRNA gene has been sequenced. The mature 16S rRNA has been found by S1 nuclease analysis to contain sequences starting from GAAGCT. The in vitro synthesized RNA has been found to protect the same nucleotides GAAGCT. In addition, the in vitro synthesized RNA was also found to strongly protect bases starting with TATG located at about 260 bases away from the start site of the mature 16S rRNA.