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PubMed2003

Phase transformation driven by valence electron concentration: tuning interslab bond distances in Gd5GaxGe4-x.

X-ray single crystal and powder diffraction studies on the Gd(5)Ga(x)()Ge(4)(-)(x)() system with 0 < or = x < or = 2.2 reveal dependence of interslab T-T dimer distances and crystal structures themselves on valence electron concentration (T is a mixture of Ga and Ge atoms). While the Gd(5)Ga(x)()Ge(4)(-)(x)() phases with 0 < or = x < or = 0.6 and valence electron concentration of 30.4-31 e(-)/formula crystallize with the Sm(5)Ge(4)-type structure, in which all interslab T-T dimers are broken (distances exceeding 3.4 A), the phases with 1 < or = x < or = 2.2 and valence electron concentration of 28.8-30 e-/formula adopt the Pu(5)Rh(4)- or Gd(5)Si(4)-type structures with T-T dimers between the slabs. An orthorhombic Pu(5)Rh(4)-type structure, which is intermediate between the Gd(5)Si(4)- and Sm(5)Ge(4)-type structures, has been identified for the Gd(5)GaGe(3) composition. Tight-binding linear-muffin-tin-orbital calculations show that substitution of three-valent Ga by four-valent Ge leads to larger population of the antibonding states within the dimers and, thus, to dimer stretching and eventually to dimer cleavage.

Journal Article↗
PubMed2000

Structural determinants required for apical sorting of an intestinal brush-border membrane protein.

The distinct protein and lipid constituents of the apical and basolateral membranes in polarized cells are sorted by specific signals. O-Glycosylation of a highly polarized intestinal brush-border protein sucrase isomaltase is implicated in its apical sorting through interaction with sphingolipid-cholesterol microdomains. We characterized the structural determinants required for this mechanism by focusing on two major domains in pro-SI, the membrane anchor and the Ser/Thr-rich stalk domain. Deletion mutants lacking either domain, pro-SI(DeltaST) (stalk-free) and pro-SI(DeltaMA) (membrane anchor-free), were constructed and expressed in polarized Madin-Darby canine kidney cells. In the absence of the membrane anchoring domain, pro-SI(DeltaMA) does not associate with lipid rafts and the mutant is randomly delivered to both membranes. Therefore, the O-glycosylated stalk region is not sufficient per se for the high fidelity of apical sorting of pro-SI. Pro-SI(DeltaST) does not associate either with lipid rafts and its targeting behavior is similar to that of pro-SI(DeltaMA). Only wild type pro-SI containing both determinants, the stalk region and membrane anchor, associates with lipid microdomains and is targeted correctly to the apical membrane. However, not all sequences in the stalk region are required for apical sorting. Only O-glycosylation of a stretch of 12 amino acids (Ala(37)-Pro(48)) juxtapose the membrane anchor is required in conjunction with the membrane anchoring domain for correct targeting of pro-SI to the apical membrane. Other O-glycosylated domains within the stalk (Ala(49)-Pro(57)) are not sufficient for apical sorting. We conclude that the recognition signal for apical sorting of pro-SI comprises O-glycosylation of the Ala(37)-Pro(48) stretch and requires the presence of the membrane anchoring domain.

Animals↗
PubMed1967

Experimental infection of the cotton rat Sigmodon hispidus with Rickettsia rickettsii.

Studies of experimental infection of the cotton rat, Sigmodon hispidus, with the virulent Sheila Smith (R type) and the avirulent Si 7 (U type) strains of Rickettsia rickettsii were undertaken to evaluate the role of this native wild mammal in the ecology of Rocky Mountain spotted fever. The Sheila Smith strain, which was highly lethal for guinea pigs, was nonpathogenic for cotton rats. Serial passage of the R-type strain in the cotton rat did not alter the virulence of the agent for cotton rats or guinea pigs. The U-type strain, which was originally recovered from a wild cotton rat, could not be maintained beyond the first passage in this animal host. Rickettsemia in the cotton rat occurred over a 24-hr period after inoculation of the virulent strain but was detected only 1 hr after inoculation of the avirulent strain. The short period of rickettsemia suggests that the cotton rat probably is not an important reservoir of R. rickettsii. Specific complement-fixing antibodies developed rapidly after infection with either strain, but the antibodies evoked by the R strain attained higher titers and persisted longer. Cotton rats previously infected with the Sheila Smith strain developed rickettsemia after reinfection with the same strain, even though relatively high levels of antibody were still present.

Animals↗
PubMed1996

Urinary symptoms, sexual intercourse and significant bacteriuria in male patients attending STD clinics.

OBJECTIVE: To assess the relationship between sexual behaviour, urinary symptoms, urinalysis and bacteriuria in men attending STD clinics. DESIGN: A prospective study recording sexual behaviour, urinary symptoms and collecting mid-stream urine specimens. SETTING: Two West Midlands STD clinics, UK. SUBJECTS: 1086 new male patients. RESULTS: 704 patients had had sexual intercourse (SI) within 14 days of testing, 424 had urinary symptoms and 122 had pyuria. All 13 patients with positive culture had SI < 14 days before testing, urinary symptoms and pyuria. No association was found between sexual orientation, type of SI, number of sexual partners, condom usage and bacteriuria. CONCLUSION: Bacteriuria does not behave as an STD but SI may be a factor in acquiring bacteriuria. Dysuria with or without urethral discharge is the most predictive symptom of bacteriuria. Pyuria has a high sensitivity for predicting bacteriuria among males.

Adolescent↗
PubMedDate not supplied

Type A/B behaviors in employed black women: comparison of blood pressures and cholesterol levels.

The purpose of this study was to examine the difference in mean blood pressure and mean cholesterol levels between Type A/B employed Black women. Data were collected on age (mean 38.76 years), weight (mean 179.28 pounds), cholesterol (mean 194.45 mg/dL), systolic blood pressures before (mean 130.68 mm Hg), during (mean 138.81 mm Hg), and after (mean 129.98 mm Hg), and diastolic blood pressure before (mean 77.11 mm Hg), during (mean 81.45 mm Hg), and after (mean 76.20 mm Hg) the Type A Structured Interview (SI) on 280 employed Black women. Audio tape analyses of the SI resulted in 136 Type A's and 144 Types B's. Each individual was screened for hypercholesteremia using a portable reflectance photometer. Blood pressure measurements were taken every minute during administration of the SI. The results indicated that Type A's had higher mean systolic blood pressures, higher diastolic blood pressures before, during and after a structured interview, and higher cholesterol levels than Types B's.

Adult↗
PubMed1984

Convergent validity of type A behavior pattern scales and their ability to predict physiological responsiveness in a sample of female public employees.

The purpose of this study was to assess the construct validity of the structured interview (SI), Jenkins Activity Survey (JAS), Thurstone Activity Scale, and Bortner Type A Scale in a sample of female employees from a government service agency. Criteria for validity assessment were physiological reactance to a mental stressor, psychological strains experienced at work, physical symptoms associated with work, and urinary catecholamine production at work. A continuous Type A SI scale demonstrated better convergent and construct validity than did the SI category scores. All of the SI Type A scales were reliable. Among the questionnaire measures only the Thurstone Activity Scale was reliable and showed the strongest construct validity. The SI measures of Type A tended to correlate with physiological responsiveness (changes in heart rate, skin temperature, and skin conductance), while the questionnaire measures correlated with self-reports of job strains (satisfaction, irritation, depression, physical symptoms), thus indicating the operation of measurement artifacts in validity assessment. No significant correlations were obtained between Type A and catecholamines. Comparison of correlation analysis with subgroup analysis revealed the former to be a more powerful test of the relationships that may exist between Type A behavior pattern and relevant criteria.

Adult↗
PubMed2004

Zr(7)Sb(4): a new binary zirconium-rich antimonide.

Zr(7)Sb(4) has been prepared by arc-melting of the elemental components and annealing at 1000-1150 degrees C. Its crystal structure was determined by X-ray diffraction (Pearson symbol mP44, monoclinic, space group P2(1)/c, Z = 4, a = 8.4905(6) A, b = 11.1557(8) A, c = 11.1217(8) A, beta = 111.443(2) degrees at 295 K). Zr(7)Sb(4) is isotypic to Hf(6)TiSb(4), a compound stabilized by differential fractional site occupancy. It is the first binary group-4 antimonide with this metal-to-antimony ratio, but it differs from the corresponding phosphides and arsenides M(7)Pn(4) (M = Ti, Zr, Hf; Pn = P, As), which adopt the Nb(7)P(4)-type structure. Zr(7)Sb(4) is built up from layers excised from the tetragonal W(5)Si(3)-type structure; these layers are displaced relative to each other to maximize interlayer Zr-Zr and Zr-Sb bonding, as confirmed by band structure calculations.

Journal Article↗
PubMed2001

Superconductivity of ternary silicide with the AlB(2)-type structure Sr(Ga(0.37),Si(0.63))(2).

A ternary silicide Sr(Ga(0.37),Si(0.63))(2) was synthesized by a floating zone method. Electron diffraction and powder x-ray diffraction measurements indicate that the silicide has the AlB(2)-type structure with the lattice constants of a = 4.1427(6) A and c = 4.7998(9) A, where Si and Ga atoms are arranged in a chemically disordered honeycomb lattice and Sr atoms are inercalated between them. The silicide is isostructural with the high-temperature superconductor MgB(2) reported recently. Electrical resistivity and dc magnetization measurements revealed that it is a type-II superconductor with onset temperature of 3.5 K.

Journal Article↗
PubMed2000

In vivo HIV-1 infection of CD45RA(+)CD4(+) T cells is established primarily by syncytium-inducing variants and correlates with the rate of CD4(+) T cell decline.

Switch from non-syncytium-inducing (NSI) to syncytium-inducing (SI) HIV type 1 (HIV-1) is associated with accelerated CD4(+) T cell depletion, which might partially be explained by higher virulence of SI variants compared with NSI variants. Because NSI and SI variants use different coreceptors for entry of target cells, altered tropism might offer an explanation for increased pathogenesis associated with SI HIV-1 infection. To investigate whether SI and NSI HIV-1 variants infect different CD4(+) T cell subsets in vivo, the distribution of SI and NSI variants over CD4(+) memory (CD45RA(-)RO(+)) and naive (CD45RA(+)RO(-)) cells was studied by using limiting dilution cultures. In contrast to NSI variants that were mainly present in CD45RO(+) cells, SI variants were equally distributed over CD45RO(+) and CD45RA(+) cells. Infection of memory cells by both NSI and SI HIV-1 and infection of naive cells primarily by SI HIV-1 corresponded closely with the differential cell surface expression of CXCR4 and CCR5. The frequency of SI-infected CD45RA(+) CD4(+) T cells, but not the frequency of NSI- or SI-infected CD45RO(+) CD4(+) T cells, correlated with the rate of CD4(+) T cell depletion. Infection of naive cells by SI HIV-1 may interfere with CD4(+) T cell production and thus account for rapid CD4(+) T cell depletion.

CD4 Lymphocyte Count↗
PubMed2000

Vertical and horizontal posture during suited immersion: similarity and differences according to some body functions.

The role of axial body orientation was weighed during acute adaptation to suit immersion (SI) in 3 hr vertical (SIv, n=4) exposure series, and 3 d experiments in which six volunteers participated in both SIv and SIh. Various types of SI recruited different hormonal mechanisms to induce similar reactions of the water-electrolyte metabolism (WEM). Changes in the body position relative to the gravity vector modified equally strength and dynamics of the WEM regulation. The experimental data suggest that osmo- and volume-regulation reactions to SIv shown the response to the actual volumetric stimulus against the "distributed" weight-bearing reaction. They are less vigorous as compared to SIh and do not reach maximum within 3 hrs. Physiological reactions to SIh were marked by greater effects of ADH on the kidney when compared with dry immersion, and an additional stimulation of aldosterone secretion by the sympathetic nervous system and/or ACTH. SIh caused rapid and more heavy symptoms of motion sickness that correlated with body mass reduction, negative water balance, degradation of tolerance of classic physical tests executed after SI. Three-days SIv, as opposed to SIh, resulted in more profound hypervolemia in the upper body of the test-subjects.

Adaptation, Physiological↗
PubMed2004

Tunable optically pumped lead-chalcogenide mid-infrared emitters on Si-substrates.

Two types of novel lead-chalcogenide mid-IR emitters grown by molecular beam epitaxy (MBE) on Si or BaF(2) substrates are described:PbSe/PbEuSe edge emitting double heterostructure (DH) and quantum well (QW) lasers are pumped optically with low-cost III-V laser-diodes. They emit in the 3-6 microm range with powers up to 200 mW. Tuning is performed by temperature change and/or mechanically if bars with slightly tapered composition are used. A "wavelength transformer", a PbSe/PbEuSe active resonant cavity with top and bottom Bragg mirror transforms the incoming 0.8 microm pump radiation to e.g. 4.2 microm wavelength. It operates at room temperature, width and value of the emission line is determined by design.

Chalcogens↗
PubMed2006

Molecular design of neutral intramolecular complexes bearing two silicon atoms anchored by a carbonyl oxygen atom: N,N'-bis(silylmethyl)propylene ureas.

B3LYP and MP2 computations have been performed on a variety of Si,Si'-substituted N,N'-bis(silylmethyl)propylene ureas. According to electron-density atoms-in-molecules (AIM) and electron localization function (ELF) quantum-topological analyses, a transition from the unstable non-chelate forms of these compounds to mono- and bis-chelate forms results in the successive interaction of one and two tetracoordinate silicon atoms with the carbonyl oxygen and the formation, respectively, of one and two covalent, polar Si...O bonds. This previously unknown X-Si<--O-->Si-X type of bonding in isomers possessing an anchor structure may be classified as a five-center, six-electron (5c-6e) bond. The factors that favor the existence of Si,Si'-substituted N,N'-bis(silylmethyl)propylene ureas exclusively in the form of stable, bridged complexes (the size of equatorial ligands and the electronegativity of axial substituents at the silicon atom, change in the donor capability of the carbonyl group, and effect of the polar solvent) are discussed.

Journal Article↗
PubMed2005

Reactions of a stable silylene with halocarbons.

An unusual product formation is observed for the insertion reaction of the thermally stable silylene Si[(NCH(2)Bu(t))(2)C(6)H(4)-1,2][abbrev. as Si(NN)] into the carbon-halogen bond of alkyl or aryl halides RHal (Hal=Cl, Br). In general, depending on the halogen, the reaction either results in a disilane of type (NN)Si(Hal)-(R)Si(NN) for Hal=Cl or a mixture of disilane and the monosilane (NN)Si(R)(Hal) for Hal=Br. The results are put into context to previously suggested mechanisms. The disilane (NN)Si(Hal)-(R)Si(NN)(Hal=Cl or Br) is thermally labile and mild thermolysis yields the corresponding monosilane (NN)Si(R)(Hal) and silylene 1. Additionally, strong evidence is presented for a radical pathway for the reaction of 1 and RHal.

Journal Article↗
PubMed1998

Proteinuria selectivity index based upon alpha 2-macroglobulin or IgM is superior to the IgG based index in differentiating glomerular diseases. Technical note.

BACKGROUND: The proteinuria selectivity index (SI) may be used to describe changes of the glomerular permeability for macromolecules in glomerular diseases. Proteins the size of alpha 2-macroglobulin (alpha 2 M) or IgM cannot normally pass the glomerular barrier, whereas IgG can pass through the large pores of glomerular basement membrane. Comparison of the clearance of the three high-molecular-weight proteins to that of albumin may be useful in characterization and diagnosis of different glomerular diseases as well as in understanding of the permeability characteristics of the glomerular filter. METHODS: Three types of SI, each calculated as a ratio of clearance of either IgG, alpha 2M or IgM to that of albumin, were measured in 199 proteinuric patients. The patients were subdivided into eight different biopsy-verified glomerular diseases. RESULTS: Two diagnoses could be clearly distinguished using SI based on alpha 2M (alpha 2 M SI) or IgM (IgM SI). Both alpha 2M SI and IgM SI were significantly lower in minimal change nephropathy and higher in crescentic necrotizing glomerulonephritis than in all the other diagnoses. The SI based on IgG (IgG SI) was less useful in determining specific diagnoses, since patients with minimal change nephropathy could not be distinguished from those with other types of primary glomerulonephritis and patients with crescentic necrotizing glomerulonephritis did not differ from those with diabetic nephropathy. CONCLUSIONS: The findings of this study indicate that alpha 2M SI and IgM SI are superior to IgG SI in characterization of glomerular disorders and might replace the IgG SI for this purpose.

Adolescent↗
PubMed2001

Layered rare-earth gallium antimonides REGaSb(2) (RE = La--Nd, Sm).

The ternary rare-earth gallium antimonides, REGaSb(2) (RE = La--Nd, Sm), have been synthesized through reaction of the elements. The structures of SmGaSb(2) (orthorhombic, space group D(5)(2)-C222(1), Z = 4, a = 4.3087(5) A, b = 22.093(4) A, c = 4.3319(4) A) and NdGaSb(2) (tetragonal, space group D(19)(4h)-I4(1)/amd, Z = 8, a = 4.3486(3) A, c = 44.579(8) A) have been determined by single-crystal X-ray diffraction. The SmGaSb(2)-type structure is adopted for RE = La and Sm, whereas the NdGaSb(2)-type structure is adopted for RE = Ce--Nd. The layered SmGaSb(2) and NdGaSb(2) structures are stacking variants of each other. In both structures, two-dimensional layers of composition (2)(infinity)[GaSb] are separated from square nets of Sb atoms [Sb] by RE atoms. Alternatively, the structures may be considered as resulting from the insertion of zigzag Ga chains between (2)(infinity)[RE Sb(2)] slabs. In SmGaSb(2), all of the Ga chains are parallel and the (2)(infinity)[SmSb(2)] layers are stacked in a ZrSi(2)-type arrangement. In NdGaSb(2), the Ga chains alternate in direction, resulting in a doubling of the long axis relative to SmGaSb(2), and the (2)(infinity)[NdSb(2)] layers are stacked in a Zr(3)Al(4)Si(5)-type arrangement. Extended Hückel band structure calculations are used to explain the bonding in the [GaSb(2)](3-) substructure.

Journal Article↗
PubMed2003

Molecular electronics on silicon: an ultrahigh vacuum scanning tunneling microscopy study.

An ultrahigh vacuum scanning tunneling microscope (STM) was employed as a tool to characterize two distinct molecular electronic strategies on the Si(100) surface. Initially, the self-directed growth of one-dimensional styrene molecular chains on hydrogen-passivated Si(100) was investigated. High-resolution empty states imaging of these styrene nanostructures confirms alignment of phenyl groups along the chain. However, attempts at STM charge transport measurements were limited by tip induced desorption of styrene molecules. Consequently, an alternative oxygen radical chemistry was also investigated. In particular, the chemical adsorption of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) onto clean Si(100) leads to the formation of an exceptionally stable silicon-oxygen bond that can withstand high bias charge transport measurements up to +/- 5 volts. Direct charge transport measurements through individual TEMPO molecules on degenerately n-type doped Si(100) reveal room temperature negative differential resistance behavior for negative sample biases exceeding - 3 volts.

Crystallography↗
PubMed1990

Self-incompatibility: a self-recognition system in plants.

Self-incompatibility (SI), a genetically controlled mechanism to prevent inbreeding in plants, offers a relatively simple model system for studying the interactions between plant cells or between a plant cell and the secreted product or products of another cell. Examples of two major types of SI, gametophytic and sporophytic, have been studied by cloning cDNAs corresponding to glycoproteins of the female tissues that segregate with particular variants encoded by the putative S locus. These secreted glycoproteins are envisaged to interact with the currently undescribed pollen component to cause arrest of pollen tube growth.

Amino Acid Sequence↗
PubMed1988

Lung volume recruitment during high-frequency oscillation in atelectasis-prone rabbits.

In diffuse lung injury, optimal oxygenation occurs with high-frequency oscillatory ventilation (HFO-A, where A is active expiratory phase) when sustained inflations (SI) are applied periodically to recruit lung volume. Theoretically pulsed pressures may be safer and more effective than static pressures for reexpanding alveoli. We compared the increases in lung volume and arterial PO2 (PaO2) induced by 30-s increases in mean airway pressure in six New Zealand White rabbits made atelectasis prone by saline lavage plus 1 h of conventional ventilation. Pulsatile SI's (HFO-A left on during increase in mean pressure) of delta PSI = 5, 10, and 15 cmH2O and static SI's (HFO-A off during SI) of delta PSI = 5, 10, 15, and 20 cmH2O were delivered in random order. Lungs were ventilated at 15 Hz, inspired fractional concentration of O2 = 1.0, and mean airway pressure 15-20 cmH2O between test periods and deflated to functional residual capacity before each SI to standardize volume history. With both maneuvers, increases in lung volume and PaO2 induced by SI's were proportional to the magnitude of the SI (P less than 0.001) in all cases. Pulsatile SI's consistently increased lung volume and PaO2 more than static SI's having the same delta PSI (P less than 0.005) such that any given target PaO2 or change in volume (delta V) was achieved at 5 cmH2O less mean pressure with the pulsatile maneuver. Respiratory system compliance increased after both types of SI. Oxygenation and lung volume changes at 5 min were related with r = 0.58 (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗