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To map the stability field of calcium ferrite-type Mg[Al.sub.2][O.sub.4] - [Mg.sub.2]Si[O.sub.4] solid solutions, high-pressure phase relations in the system Mg[Al.sub.2][O.sub.4] - [Mg.sub.2]Si[O.sub.4] were studied in the compositional range of 0 to 50 mol% [Mg.sub.2]Si[O.sub.4]. The calcium ferrite solid solutions are stable above 23 GPa at 1600[degrees]C, and the maximum solubility of [Mg.sub.2]Si[O.sub.4] component in Mg[Al.sub.2][O.sub.4] calcium ferrite is 34 mol%. Lattice parameters and unit-cell volume of calcium ferrite-type Mg[Al.sub.2][O.sub.4] (space group Pbnm) determined by Rietveld analysis are a = 9.9498(6) [Angstrom], b = 8.6468(6) [Angstrom], c = 2.7901(2) [Angstrom], and V = 240.02(2) [[Angstrom].sup.3]. Lattice parameters for the Mg[Al.sub.2][O.sub.4] - [Mg.sub.2]Si[O.sub.4] solid solutions with the compositions of 14, 24, and 34 mol% [Mg.sub.2]Si[O.sub.4] indicated the following compositional dependency of lattice parameters: [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] where [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] is the mole fraction of [Mg.sub.2]Si[O.sub.4] component. A linear extrapolation of the composition-molar volume relationship gave an estimated volume of 36.49(2) [cm.sup.3]/mol for the hypothetical calcium ferrite-type [Mg.sub.2]Si[O.sub.4]. This value is larger than that of the isochemical mixture of MgSi[O.sub.3] perovskite and MgO, 35.72(1) [cm.sup.3]/mol. This implies that the mixture of MgSi[O.sub.3] perovskite and MgO is more stable than the hypothetical calcium ferrite-type [Mg.sub.2]Si[O.sub.4] under the lower mantle conditions. Keywords: Mg[Al.sub.2][O.sub.4], [Mg.sub.2]Si[O.sub.4], calcium ferrite, high pressure, phase relation, Rietveld refinement

With growing understanding of the differences between solid residues from the fluidized bed combustion of petroleum coke and of coal, the significance of fuel-derived and sorbent-derived components of the ash has become clearer. It is well documented that hydration of the ashes is necessary prior to disposal or utilization or as a reactivation method. Initially, hydration of the lime was thought to involve water reacting only with CaO to form Ca[(OH).sub.2] but when the free lime content of the ashes is looked at before and after hydration, it is apparent that the process is more complex. Detailed analyses have shown that the free lime can decrease and vary within the same ash in different particle size ranges. The complexity of the reactions is reflected in problems with the assessment of the free lime content of the materials and the effect of hydration on different particle size fractions of the ash. The free lime content of the ash is significantly lower than expected based on the elemental analysis. Bed ash from the circulating fluidized bed combustion boilers owned and operated by the Nelson Industrial Steam Company Ltd. (NISCO) was examined in detail to elucidate the fate of calcium in the ash during hydration, using a range of techniques. The objective of the study is to determine the amount of CaO available for hydration/reactivation and to better understand interactions of Ca and other mineral components of the ash. Analysis results indicate that in NISCO ashes up to about 6% of the analytical CaO may be combined as acid soluble and insoluble OCCs (other calcium compounds). This implies up to about 10% less free lime than would be inferred from standard chemical analyses. About 1% of the missing CaO can be present as acid insoluble Ca and Mg vanadates, with up to 2% bound in soluble OCCs. The remaining 3-4% is still not accounted for. It is clear that even very minor quantities of mineral matter, other than CaO or Ca[SO.sub.4], associated mainly with the coarser size fractions, are important. The amount of bound water in the hydrated ash, other than that combined in portlandite or brucite, can be as large as 3-5%. This cannot be ignored when sample mass change on hydration or heating is used as a measure of the extent of CaO to Ca[(OH).sub.2] conversion. [DOI: 10.1115/1.2358144] Keywords: petroleum coke, FBC ash, calcium balance, free lime, hydration, Ca[(OH).sub.2], vanadium

High-pressure phase stabilities of the CaSn[O.sub.3] system were investigated using density functional theory static lattice energy calculations. We have identified six phase changes in this system: perovskite-post-perovskite, post-perovskite-B2+cotunnite in CaSi[O.sub.3], B1-B2 in CaO, cassiterite-pyrite, pyrite-orthorhombic-I, and orthorhombic-I-cotunnite in Sn[O.sub.2]-. Our results demonstrate a new high-pressure phase sequence of perovskite [right arrow] post-perovskite [right arrow] B2 + cotunnite. The post-perovskite transformation occurs at ~12 GPa with ~2.5% volume reduction and then it decomposes into the oxide mixture of B2 CaO and cotunnite Sn[O.sub.2] at ~70 GPa with 8.1% volume reduction. The results also predict a few percent bulk velocity variations across these phase changes. Keywords: CaSn[O.sub.3], perovskite, post-perovskite, density functional calculation

The [Ca.sup.2} -dependent membrane interactions of a water soluble fragment of synaptotagmin I (C2AB), containing two C2 domains (C2A and C2B) was determined using site-directed spin labeling. The data showed that C2A and C2B are not independent in nature but influence their mutual membrane penetration, explaining occurrence of multiple C2 domains in proteins, which function in membrane trafficking and repair.

In some cell types, oscillations in the concentration of free intracellular calcium ([[Ca.sup.2+]]) are accompanied by oscillations in the concentration of inositol 1,405-trisphosphate ([I[P.sub.3]]). However, in most cell types it is still an open question as to whether oscillations in [I[P.sub.3]] are necessary for [Ca.sup.2+] oscillations in vivo, or whether they merely follow passively. Using a wide range of models, we show that the response to an artificially applied pulse of I[P.sub.3] can be used to distinguish between these two cases. Hence, we show that muscarinic receptor-mediated, long-period [Ca.sup.2+] oscillations in pancreatic acinar cells depend on [I[P.sub.3]] oscillations, whereas shortperiod [Ca.sup.2+] oscillations in airway smooth muscle do not. mathematical model

Corn tortillas are the staple food of Mexico. During their preparation, calcium is added to the tortillas; therefore, tortillas are the main source of calcium for a large proportion of the population. The bioavailability of calcium from lime-treated tortillas in humans is not known. The objectives of the present study were to determine calcium absorption from corn tortilla, to determine the effect of lime treatment on calcium absorption from corn tortilla, and to compare calcium absorption from tortilla prepared with a commercial corn flour and tortillas prepared with the traditional lime treatment at home. Nonpregnant, nonlactating women (n = 9) were administered 3 different treatments: 1) 180 g of corn tortilla prepared from corn flour with no lime treatment (CF), 2) 180 g of corn tortilla prepared from lime-treated commercial corn flour (LTCCF), or 3) 180 g of corn tortillas prepared from lime-treated home-prepared corn flour (LTHCF). Calcium absorption was measured using an established dual-tracer stable isotope technique. Calcium absorption of CF, LTCCF, and LTHCF was (mean [+ or -] SD): 44 [+ or -] 3.2, 32 [+ or -] 4.4, and 30 [+ or -] 2.4%, respectively; the fractional calcium absorption from CF differed from that of either LTCCF or LTHCF (P < 0.01). The total amount of calcium absorbed per treatment was higher in LTHCF (98.10 mg [+ or -] 21.7) than in LTCCF (59.9 mg [+ or -] 23.7, P < 0.001) and CF (3.78 mg [+ or -] 0.9, P < 0.0.001). In conclusion, calcium absorption from corn tortillas is high and dependent on calcium concentration. The addition of calcium during lime treatment increases calcium concentration and total calcium absorption. KEY WORDS: * calcium absorption * tortillas * lime treatment * stable isotopes

The InsP3 receptor is a ligand-gated channel that releases Ca(super 2+) from intracellular stores in a variety of cell types, including neurons. Genetic studies from vertebrate and invertebrate model systems suggest that coordinated rhythmic motor functions are most susceptible to changes in Ca(super 2+) release from the InsP3 receptor.

The contributions of Ca(super 2+) and Ca(super 2+) binding proteins to health and disease were addressed in a meeting held in April 2005 in Bnaff, Canada. Insights got from the mechanical studies offered the potential for new therapeutic approaches to combat a variety of diseases resulting from alterations in Ca(super 2+) homeostasis.

Light stimuli produce graded hyperpolarizations of the photoreceptor plasma membrane and an associated decrease in a voltage-gated calcium channel conductance that mediates release of glutamate neurotransmitter. The [Ca.sub.v]1.4 channel is thought to be involved in this process. The CACNA1F gene encodes the pore-forming subunit of the [Ca.sub.v]1.4 channel and various mutations in CACNA1F cause X-linked incomplete congenital stationary night blindness (CSNB2). The molecular mechanism of the pathology underlying the CSNB2 phenotype remains to be established. Recent clinical investigations of a New Zealand family found a severe visual disorder that has some clinical similarities to, but is clearly distinct from, CSNB2. Here, we report investigations into the molecular mechanism of the pathology of this condition. Molecular genetic analyses identified a previously undescribed nucleotide substitution in CACNA1F that is predicted to encode an isoleucine to threonine substitution at CACNA1F residue 745. The I745T CACNA1F allele produced a remarkable approximately -30-mV shift in the voltage dependence of [Ca.sub.v]1.4 channel activation and significantly slower inactivation kinetics in an expression system. These findings imply that substitution of this wild-type residue in transmembrane segment IIS6 may have decreased the energy required to open the channel. Collectively, these findings suggest that a gain-of-function mechanism involving increased [Ca.sub.v]1.4 channel activity is likely to cause the unusual phenotype.

Ca(super 2+) regulation of erythrocyte AMP deaminase [isoform E (AMPD3)] was studied by examining in vitro effects of calmodulin (CaM) on the enzyme and by monitoring the influence of CaM antagonists on purine catabolic flow in freshly prepared erythrocytes under various conditions of energy imbalance. The results suggested a protein-protein interaction between Ca(super 2+) -CaM and isoform E.

To investigate the effects of chronic exposure to ketone bodies on glucose-induced insulin secretion, we evaluated insulin release, intracellular [Ca.sup.2+] and metabolism, and [Ca.sup.2+] efficacy of the exocytotic system in rat pancreatic islets. Fifteen-hour exposure to 5 mM D-[beta]-hydroxybutyrate (HB) reduced high glucose-induced insulin secretion and augmented basal insulin secretion. Augmentation of basal release was derived from promoting the [Ca.sup.2+]-independent and ATP-independent component of insulin release, which was suppressed by the GDP analog. Chronic exposure to HB affected mostly the second phase of glucose-induced biphasic secretion. Dynamic experiments showed that insulin release and NAD(P)H fluorescence were lower, although the intracellular [Ca.sup.2+] concentration ([[[Ca.sup.2+]].sub.i]) was not affected 10 min after exposure to high glucose. Additionally, [[[Ca.sup.2+]].sub.i] efficacy in exocytotic system at clamped concentrations of ATP was not affected. NADH content, ATP content, and ATP-to-ADP ratio in the HB-cultured islets in the presence of high glucose were lower, whereas glucose utilization and oxidation were not affected. Mitochondrial ATP production shows that the respiratory chain downstream of complex II is not affected by chronic exposure to HB, and that the decrease in ATP production is due to decreased NADH content in the mitochondrial matrix. Chronic exposure to HB suppresses glucose-induced insulin secretion by lowering the ATP level, at least partly by inhibiting ATP production by reducing the supply of NADH to the respiratory chain. Glucose-induced insulin release in the presence of aminooxyacetate was not reduced, which implies that chronic exposure to HB affects the malate/aspartate shuttle and thus reduces NADH supply to mitochondria. islet; reduced nicotinamide adenine dinucleotide; adenosine 5'-triphosphate

Identification of the mechanisms involved in the pathology of nutrient deficiency provides an understanding of nutrient functions, their role in metabolism, and interactions between nutrients. However, evidence has emerged in recent years that low (suboptimal) intakes of micronutrients are associated with an elevated risk of chronic diseases. The description of micronutrient associations with chronic disease as a deficiency disease does not capture the complexity of these relations. It implies a significant oversimplification of this relation and detracts from the need for development of new approaches to this area of study. Epidemiologic study designs are essential for progress in understanding the micronutrient--chronic-disease relations, and these are described. Two areas wherein epidemiological tools could be incorporated into experimental designs have been vitamin D and prostate cancer, and vitamin D and colon cancer. In each case, biomarkers of exposure, intermediary markers, and mechanisms have been identified and could be implemented in new experimental designs. Measures of exposure would be improved by incorporation of measurements of vitamin D status such as serum 25-hydroxyvitamin D measurements. Several intermediary markers are discussed and may be useful in the characterization of responses. Such developments should aid in the interpretation of studies and identify vitamin D, as well as calcium intakes, that will aid in the prevention of prostate and colon cancer. KEY WORDS: * vitamin D * prostate cancer * colon cancer * biomarkers * epidemiology

The major plasma membrane Ca(super 2)+ extruding system, the Na+/Ca(super 2)+ exchanger (NCX) that is cleared during brain ischemia and in neurons undergoing excitotoxicity is described. Proteolytic inactivation of NCX-driven neuronal Ca(super 2)+ extrusion is responsible for the delayed excitotoxic Ca(super 2)+ deregulation and neuronal death.

A study is conducted to investigate the structural and functional significance of the five cysteine residues present in the Ca(super 2+) binding protein, Human calbindin D28k through a series of cysteine-to-serine mutations. The mutants are studied under relevant physiological redox potentials in which conformational changes are monitored using ANS binding.

Analysis of the hystereses in the force-length relationship at constant [Ca.sup.2+] concentration and in the force-calcium relationship at constant sarcomere length (SL) provides insight into the mechanisms that control cross-bridge (XB) recruitment. The hystereses are related here to two mechanisms that regulate the number of strong XBs: the cooperativity, whereby the number of strong XBs determines calcium affinity, and the mechanical feedback, whereby the shortening velocity determines the duration for which the XBs are in the strong state. The study simulates the phenomena and defines the role of these feedbacks. The model that couples calcium kinetics with XB cycling was built on Simulink software (Matlab). Counterclockwise (CCW) hysteresis, wherein the force response lags behind the SL oscillations, at a constant calcium level, is obtained in the force-length plane when neglecting the mechanical feedback and accounting only for the cooperativity mechanism. Conversely, the force response precedes the SL oscillations, yielding a clockwise (CW) hysteresis when only the mechanical feedback is allowed to exist. In agreement with experimental observations, either CW or CCW hysteresis is obtained when both feedbacks coexist: CCW hystereses are obtained at low frequencies (3 Hz). The cooperativity dominates at low frequencies and allows the muscle to adapt XB recruitment to slow changes in the loading conditions. The changeover frequency from CCW to CW hysteresis defines the velocity limit above which the muscle absorbs rather than generates energy. The hysteresis in the force-calcium relation is conveniently explained by the same cooperativity mechanism. We propose that a single cooperativity mechanism that depends on the number of strong XBs can explain the hystereses in the force-length as well as in the force-calcium relationships. excitation-contraction coupling; regulated actin; work loop; force-length relationship

The linker region and the C-terminus of cysteine string proteins (Csp) are interfering with exocytosis and could assign two functions to the C-terminus in Ca(super 2+)-simulated cells, that is the interaction with SNARE protein VAMP and modulation of Csp homodeimerization. Cross-linking in permeabilized clonal beta-cells revealed homodeimerization of Csp, which is stimulated by Ca(super 2+) and again modulated by the variant C-terminus.

Polarized Sr EXAFS on oriented Sr-reactivated samples show that Fourier peak II, which fits best to Mn at 3.5 A[ring] rather than lighter atoms, is dichroic, with a larger magnitude at 10 degree and a smaller magnitude at 80 degree. Ca (Sr) is proximal to the Mn cluster and lead to refined working models of the heteronuclear Mn4Ca cluster of the oxygen-evolving complex in PS II.

By immersing ether Au(111) or Au(100) substrate into benzene ad layers of 15-crown 15-ether- substituted cobalt (II) phtalocyanine (CoCRPc) were prepared. Relationship between CRPc and Au lattice is significant in trapping of Ca(super 2+) ions in crown rings.

The very different courtship flashes of Photuris versicolor and Photuris lucicrescens males mirror the pattern of neural impulses produced by their brain. Their lanterns luminescence very differently, however, in response to direct, electrical stimulation. Whereas P. lucicrescens lanterns glow in response to high frequency, continuous electrical stimulation, those of P. versicolor produce only rapid, triple-pulsed flashlettes that resemble, but are not identical to, their courtship flashes. In addition, the exposed lantern tissue of P. versicolor males, when immersed in firefly saline high in potassium and calcium ions, scintillates with hundreds of photocytes flashing in random fashion. P. lucicrescens male lanterns, so treated, only glow. Tests of P. versicolor lanterns with salines of different composition suggest that calcium ions are essential in producing this intense, long lasting scintillation response and are therefore possibly implicated in the final stages of flash control in this species.

The role of adenosine 5-triphosphate (ATP) in the activation mechanism of alpha-ca(super 2+)/calmodulin-dependent protein kinase II(alpha CaMKII) was investigated using the T286A non-autophosphorytable mutant of alphaCaMKII. Electron micrographic images of negatively stained T286A-alphaCaMKII mutant protein had a similar appearance to those of dodecameric alphaCaMKII.

The high-resolution laser-induced fluorescence spectrum of a molecular beam sample of calcium monohydride (CaH) in the region of the strongly overlapped (1,0) [A.sup.2][PHI] - [X.sup.2][[SIGMA].sup.+] and (0,0) [B.sup.2][[SIGMA].sup.+] - [X.sup.2][[SIGMA].sup.+] band systems near 63 nm and the (0,0) [A.sup.2][PHI] - [X.sup.2][[SIGMA].sup.+] band system near 690 nm have been recorded and analyzed. The spectral features exhibit a small splitting that is attributed to proton magnetic hyperfine interaction in the [X.sup.2][[SIGMA].sup.+] (v = 0) state. The energy levels of the [A.sup.2][PHI](v = 0) vibronic state were modeled using a traditional "effective" Hamiltonian approach, whereas those for the interacting [A.sup.2][PHI](v = 1)/[B.sup.2][[SIGMA].sup.+] (v = 0) vibronic levels were modeled by augmenting the traditional effective Hamiltonian with terms to account for local perturbations. An interpretation of the field-free parameters is presented. Key words: calcium monohydride, molecular beam, fluorescence.

The performance of a selection of theoretical procedures in describing the binding of Ca(super 2+) to ammonia and formaldehyde was assessed. Ca(super 2+) was predicted to bind more strongly to formaldehyde than to ammonia, in contrast to the ordering of proton and Li(super +1) affinities for the two molecules.

Interaction between the surface of the calcium pyrophosphate dihydrate (CPPD) crystals and the extracellular layer of the hydrated dimyristoyl phosphatidylcholin (DMPC) phospholipid bilayer is studied by using molecular dynamics (MD).

Small-angle X-ray scattering (SAXS) is used to study the structure of a complex formed from DNA, calcium and DPPC. The effects of calcium on lipids are studied.

Ryanodine receptors (RyRs) are Ca(super ++) channels that control cellular functions. An estimation of the RyR2 ion diffusion constants and electrostatic interactions, in a self-consistent coherent formulation, is provided by the extended PNP.

Elevated extracellular calcium ([[[Ca.sup.2+]].sub.o]) and other agonists potentially acting via the calcium-sensing receptor (CAR) increase parathyroid hormone-related peptide (PTHrP) release from H-500 Leydig cells. Here, we provide strong evidence for the CaR's involvement by using a dominant negative CaR that attenuates high [[[Ca.sup.2+]].sub.o]-induced PTHrP release. This effect is likely transcriptional, because high [[[Ca.sup.2+]].sub.o] upregulates the PTHrP transcript, an effect that is abolished by actinomycin D. Regulation of PTHrP release by the CaR involves activation of PKC as well as ERK1/2, p38 MAPK, and JNK pathways. However, we show for the first time that high [[[Ca.sup.2+]].sub.o]-induced activation of the stress-activated protein kinase SEK1 is PKC independent, because there is an additive effect of a PKC inhibitor in combination with the JNK inhibitor on [[[Ca.sup.2+]].sub.o]-stimulated PTHrP release. Furthermore, high [[[Ca.sup.2+]].sub.o], in a PKC-independent fashion, induces phosphorylation of ERK1/2, SEK1, p38 MAPK, and its downstream transcription factor ATF-2. We conclude that CaR regulation of PTHrP release in H-500 cells involves activation of PKC as well as the ERK1/2, p38 MAPK, and JNK pathways. G protein-coupled receptor; Leydig cells; humoral hypercalcemia of malignancy; dominant negative; stress-activated protein kinase activator 1; osteolysis

Extracellular nucleotide-activated purinergic receptors (P2XRs) are a family of cationpermeable channels that conduct small cations, including [Ca.sup.2+], leading to the depolarization of cells and subsequent stimulation of voltage-gated [Ca.sup.2+] influx in excitable cells. Here, we studied the spatiotemporal characteristics of intracellular [Ca.sup.2+] signaling and its dependence on current signaling in excitable mouse immortalized gonadotropin-releasing hormone-secreting cells (GT1) and nonexcitable human embryonic kidney cells (HEK-293) cells expressing wild-type and chimeric P2XRs. In both cell types, P2XR generated depolarizing currents during the sustained ATP stimulation, which desensitized in order (from rapidly desensitizing to nondesensitizing): [P2X.sub.3]R > [P2X.sub.2b] + [X.sub.4]R > [P2X.sub.2b]R > [P2X.sub.2a] + [X.sub.4]R > [P2X.sub.4]R > [P2X.sub.2a]R > [P2X.sub.7]R. HEK-293 cells were not suitable for studies on P2XR-mediated [Ca.sup.2+] influx because of the coactivation of endogenously expressed [Ca.sup.2+]-mobilizing purinergic P2Y receptors. However, when expressed in GT1 cells, all wild-type and chimeric P2XRs responded to agonist binding with global [Ca.sup.2+] signals, which desensitized in the same order as current signals but in a significantly slower manner. The global distribution of [Ca.sup.2+] signals was present independently of the rate of current desensitization. The temporal characteristics of [Ca.sup.2+] signals were not affected by voltage-gated [Ca.sup.2+] influx and removal of extracellular sodium. [Ca.sup.2+] signals reflected well the receptor-specific [EC.sub.50] values for ATP and the extracellular [Zn.sup.2+] and pH sensitivities of P2XRs. These results indicate that intracellular [Ca.sup.2+] measurements are useful for characterizing the pharmacological properties and messenger functions of P2XRs, as well as the kinetics of channel activity, when the host cells do not express other members of purinergic receptors. ATP-gated receptor channels; inward currents; intracellular calcium signals; desensitization-inactivation; voltage-gated calcium influx; localized and global calcium signals

Osteoclasts are multinucleated, bone-resorbing cells that show structural and functional differences between the resorbing and nonresorbing (motile) states during the bone resorption cycle. In the present study, we measured intracellular [Ca.sup.2+] concentration ([[[Ca.sup.2+]].sub.i]) in nonresorbing vs. resorbing rat osteoclasts. Basal [[[Ca.sup.2+]].sub.i] in osteoclasts possessing pseudopodia (nonresorbing/motile state) was around 110 nM and significantly higher than that in actin ring-forming osteoclasts (resorbing state, around 50 nM). In nonresorbing/motile osteoclasts, exposure to high [K.sup.+] reduced [[[Ca.sup.2+]].sub.i], whereas high [K.sup.+] increased [[[Ca.sup.2+]].sub.i] in resorbing state osteoclasts. In nonresorbing/motile cells, membrane depolarization and hyperpolarization applied by the patch-clamp technique decreased and increased [[[Ca.sup.2+]].sub.i], respectively. Removal of extracellular [Ca.sup.2+] or application of 300 [micro]M [La.sup.3+] reduced [[[Ca.sup.2+]].sub.i] to ~50 nM in non-resorbing/motile osteoclasts, and high-[K.sup.+]-induced reduction of [[[Ca.sup.2+]].sub.i] could not be observed under these conditions. Neither inhibition of intracellular [Ca.sup.2+] stores or plasma membrane [Ca.sup.2+] pumps nor blocking of L- and N-type [Ca.sup.2+] channels significantly reduced [[[Ca.sup.2+]].sub.i]. Exposure to high [K.sup.+] inhibited the motility of nonresorbing osteoclasts and reduced the number of actin rings and pit formation in resorbing osteoclasts. These results indicate that in nonresorbing/ motile osteoclasts, a [La.sup.3+]-sensitive [Ca.sup.2+] entry pathway is continuously active under resting conditions, keeping [[[Ca.sup.2+]].sub.i] high. Changes in membrane potential regulate osteoclastic motility by controlling the net amount of [Ca.sup.2+] entry in a 'reversed' voltage-dependent manner, i.e., depolarization decreases and hyperpolarization increases [[[Ca.sup.2+]].sub.i]. membrane depolarization; resorbing and motile activities; bone resorbing cycle

A study of the uderpotential depostion (UPD) of Te monolayers onto Au electrodes from perchloric acid solution using electrochemical quartz microgravimetry (EQCM) and chronocoulometry is reported. Analysis of the current time data indicates that this process occurs by a two-dimensional instantaneous nucleation and growth mechanism, resulting in an ordered overlayer with a fractional coverage of ca. 0.41.

The refractive indices of synthetic calcium fluoride for 69 wavelengths from 138 nm in the deep ultraviolet to 2326 nm in the near infrared were measured by the minimum-deviation method in a nitrogen environment. We made these measurements at 20[degrees] and 25[degrees]C, respectively, to determine the thermal coefficients of the refractive index over this wide-wavelength region. These refractive indices were fitted to a four-term Sellmeier dispersion formula. The temperature coefficients of the refractive index were fitted to a Hoffman-type dispersion formula. The standard deviation of the residual between the observed values and the calculated values was 0.6 [10.sup.-6] for the refractive index and was 0.13 [10.sup.-6]/[degrees] C for the temperature coefficient of the refractive index.

We have studied short-range cation ordering across the diopside (CaMg[Si.sub.2][O.sub.6]-Ca-Tschermak pyroxene (Ca[Al.sub.2]Si[O.sub.6]) (Di-CaTs) solid solution in samples synthesized at 1400 [degrees] C and 2 GPa, for 24 hours. Peak positions in [sup.29]Si MAS NMR spectra are sensitive to Al substitution, both in the corner-sharing NN tetrahedral sites on the single chain and in one of the three NN octahedral M1 sites. The substitution of A1 for Mg on MI causes the [sup.29]Si chemical shift to be shielded by about the same magnitude as the deshielding caused by substitution of Al for Si in NN tetrahedra, causing severe peak overlap among central peaks. Two pairs of the unique local environments have very similar chemical shifts, leaving only four peaks resolved in the spectrum, for which six site assignments have been made. [sup.29]Si MAS NMR peak intensities for end-member CaTs are consistent with 70% of the Si in the tetrahedral chain being locally ordered into alternating [sup.[4]]AI-O-Si-O-[sup.[4]]Al linkages, although space group C2/c would suggest that Si and Al are long-range disordered over the tetrahedral chain. CaTs clearly violates Lowenstein's (1954) Al-O-Al avoidance principle, with 0.175 Al-O-Al linkages per formula unit (based on six O atoms per formula unit), as calculated from observed [sup.29]Si MAS NMR peak intensities. For intermediate members of the solid solution, site populations have been modeled using a random distribution model (RD), an Al-O-Al avoidance model (AA) and a modified AA model which couples the cation distribution between the tetrahedral and octahedral sites (AAOC). The RD model fits the [sup.29]Si MAS NMR peak intensities poorly. The AA and AAOC models fit the [sup.29]Si NMR data well to at least 75% CaTs, suggesting that diopside-rich Di-CaTs clinopyroxenes obey Lowenstein's Al-O-Al avoidance principle. For compositions >75% CaTs, observed cation distributions deviate considerably from that predicted by Al-O-Al avoidance, indicating formation of Al-O-Al linkages. The AAOC model yields an improved fit to the observed [sup.29]Si MAS NMR intensities, particularly near [Di.sub.50]Ca[Ts.sub.50], implying the presence of [sup.[4]]Si-O-[sup.[6]]Mg and [sup.[4]]AI-O-[sup.[6]]A1 couples. This suggests the presence of short-range ordering on both tetrahedral and octahedral sites in Di-CaTs pyroxenes. The high sensitivity to octahedral Al substitution observed in these chain silicates is not observed by [sup.29]Si MAS NMR of more-polymerized silicates, such as framework and sheet structures. Thus, [sup.[29]]Si MAS NMR of pyroxenes has potential to reveal tetrahedral-octahedral cation coupling and octahedral cation ordering information, which is potentially important for geothermobarometry of aluminous pyroxenes.

Three types of calcium carbonyl complexes are formed due to adsorption of CO on CaNaY at 85K. These three principle bands are formed in the carbonyl stretching region at 2185, 2167 and 2145 cm-1.

Three new calcium germanium nitrides from molten sodium are synthesized and very different structural motifs and oxidation states as attainable in ternary germanium nitrides are determined. Ca(sub 2)GeN(sub 2) contain structural motifs which appear to be characteristic of nitride chemistry, Ca(sub 4)GeN(sub 4) is a nitride analogue of orthosilicates and orthogermanates but with no direct structural relative in those classes of compounds while Ca(sub 5)Ge(sub 2)N(sub 6) can be considered as the first nitride analogue of the pyroxene class of silicates.

Pyrazolato complexes of calcium are prepared through treatment of calcium bromide with pyrazolato-potassium reagents in the presence of neutral donor ligands. X-ray crystal structures reveal monomeric formulations with eta(super 2)-pyrazolato ligand coordination.

Researchers in Pennsylvania examined the role of calcium arsenate formation in the order to to reduce dissolved arsenic in water.

The magnetic frustration effects in the La(sub 1-x)Ca(sub x)MnO3 (x=0.2,0.3) single crystals from dc and ac susceptibility measurements are investigated. It was seen that the magnetic transition around 100 K involving probably charge-ordered phase was affected by the frequency and the spin dynamics of La(sub 0.8)Ca(sub 0,2)MnO3 that changed drastically at high frequencies (approximately at 10 KHz).

(001) substrate as a function of film thickness (50 and 100 nm) and oxygen content (optimum and reduced) is investigated using magnetic force microscopy. The domain nucleation and growth takes place by discrete reorientation of regions that have diameters similar to the final domain width.

Low-angle inelastic neutron scattering was used to study the temperature and wave vector dependence of the spin waves in La(sub 0.67)Ca(sub 0.33)MnO(sub 3) perovskite-based colossal magnetoresistance material. Detailed neutron measurements of the order parameter in zero applied field showed a similar first-order like transition.

Ultrafine La(sub 0.7)Ca(sub 0.3)MnO(sub z) powders with controlled oxygen stoichiometry are synthesized by mechanical alloying at ambient temperature. These observations are discussed in terms of magnetic disorder resulting from defects induced by high-energy milling and surface effects dominant in small crystals.