bluuebunny/crossref_metadata_2025 huggingface dataset:
A MAP4 kinase related to Ste20 is a nutrient-sensitive regulator of mTOR signalling
Authors: Findlay Greg M. , Yan Lijun , Procter Julia , Mieulet Virginie , Lamb Richard F.
Published: March 2007

The mTOR (mammalian target of rapamycin) signalling pathway is a key regulator of cell growth and is controlled by growth factors and nutrients such as amino acids. Although signalling pathways from growth factor receptors to mTOR have been elucidated, the pathways mediating signalling by nutrients are poorly characterized. Through a screen for protein kinases active in the mTOR signalling pathway in Drosophila we have identified a Ste20 family member (MAP4K3) that is required for maximal S6K (S6 kinase)/4E-BP1 [eIF4E (eukaryotic initiation factor 4E)-binding protein 1] phosphorylation and regulates cell growth. Importantly, MAP4K3 activity is regulated by amino acids, but not the growth factor insulin and is not regulated by the mTORC1 inhibitor rapamycin. Our results therefore suggest a model whereby nutrients signal to mTORC1 via activation of MAP4K3.
Manipulation of host signalling pathways by anthrax toxins
Authors: Turk Benjamin E.
Published: March 2007

Infectious microbes face an unwelcoming environment in their mammalian hosts, which have evolved elaborate multicelluar systems for recognition and elimination of invading pathogens. A common strategy used by pathogenic bacteria to establish infection is to secrete protein factors that block intracellular signalling pathways essential for host defence. Some of these proteins also act as toxins, directly causing pathology associated with disease. Bacillus anthracis, the bacterium that causes anthrax, secretes two plasmid-encoded enzymes, LF (lethal factor) and EF (oedema factor), that are delivered into host cells by a third bacterial protein, PA (protective antigen). The two toxins act on a variety of cell types, disabling the immune system and inevitably killing the host. LF is an extraordinarily selective metalloproteinase that site-specifically cleaves MKKs (mitogen-activated protein kinase kinases). Cleavage of MKKs by LF prevents them from activating their downstream MAPK (mitogen-activated protein kinase) substrates by disrupting a critical docking interaction. Blockade of MAPK signalling functionally impairs cells of both the innate and adaptive immune systems and induces cell death in macrophages. EF is an adenylate cyclase that is activated by calmodulin through a non-canonical mechanism. EF causes sustained and potent activation of host cAMP-dependent signalling pathways, which disables phagocytes. Here I review recent progress in elucidating the mechanisms by which LF and EF influence host signalling and thereby contribute to disease.
(Peri)vascular production and action of pro-inflammatory cytokines in brain pathology
Authors: Konsman Jan P. , Drukarch Benjamin , Van Dam Anne-Marie
Published: March 2007

In response to tissue injury or infection, the peripheral tissue macrophage induces an inflammatory response through the release of IL-1β (interleukin-1β) and TNFα (tumour necrosis factor α). These cytokines stimulate macrophages and endothelial cells to express chemokines and adhesion molecules that attract leucocytes into the peripheral site of injury or infection. The aims of the present review are to (i) discuss the relevance of brain (peri)vascular cells and compartments to bacterial meningitis, HIV-1-associated dementia, multiple sclerosis, ischaemic and traumatic brain injury, and Alzheimer's disease, and (ii) to provide an overview of the production and action of pro-inflammatory cytokines by (peri)vascular cells in these pathologies of the CNS (central nervous system). The brain (peri)vascular compartments are highly relevant to pathologies affecting the CNS, as infections are almost exclusively blood-borne. Insults disrupt blood and energy flow to neurons, and active brain-to-blood transport mechanisms, which are the bottleneck in the clearance of unwanted molecules from the brain. Perivascular macrophages are the most reactive cell type and produce IL-1β and TNFα after infection or injury to the CNS. The main cellular target for IL-1β and TNFα produced in the brain (peri)vascular compartment is the endothelium, where these cytokines induce the expression of adhesion molecules and promote leucocyte infiltration. Whether this and other effects of IL-1 and TNF in the brain (peri)vascular compartments are detrimental or beneficial in neuropathology remains to be shown and requires a clear understanding of the role of these cytokines in both damaging and repair processes in the CNS.
Enhanced cardiac production of matrix metalloproteinase-2 and -9 and its attenuation associated with pravastatin treatment in patients with acute myocardial infarction
Authors: Yasuda Satoshi , Miyazaki Shunichi , Kinoshita Hideyuki , Nagaya Noritoshi , Kanda Munetake , Goto Yoichi , Nonogi Hiroshi
Published: March 2007

Previous experimental studies have demonstrated that MMPs (matrix metalloproteinases) contribute to LV (left ventricular) remodelling. We hypothesized that cardiac MMPs are activated in patients with AMI (acute myocardial infarction) and, if so, MMP production may be attenuated by statins (3-hydroxy-3-methylglutaryl-CoA reductase inhibitors) through their cardiovascular protective actions. We studied 30 patients, ten control patients with stable angina pectoris and 20 patients with AMI, in whom LV catheterization at the chronic stage was performed 22±12 days (value is mean±S.D.) after the onset of AMI. Blood samples were collected from the CS (coronary sinus) and a peripheral artery. In patients with AMI, the levels of MMP-2 and MMP-9 were significantly (P<0.05) higher in the CS than the peripheral artery (MMP-2, 853±199 compared with 716±127 ng/ml; MMP-9, 165±129 compared with 98±82 ng/ml), whereas no significant differences were observed in the patients with angina pectoris. The CS–arterial concentration gradients of MMP-2 and MMP-9 correlated positively with BNP (brain natriuretic peptide) levels (MMP-2, R=0.68, P<0.01; MMP-9, R=0.59, P<0.05) and LV end-diastolic volume index (MMP-2, R=0.70, P<0.01; MMP-9, R=0.70, P<0.01). When patients with AMI treated with 10 mg of pravastatin or without (n=10 in each group) were compared, this statin therapy significantly (P<0.05) decreased the CS–arterial concentration gradients of MMP-2 (69±43 compared with 213±185 ng/ml) and MMP-9 (14±27 compared with 119±84 ng/ml). In conclusion, the enhanced production of cardiac MMP-2 and MMP-9 is associated with LV enlargement and elevated BNP levels in patients with AMI. A pleiotropic effect of statins appears to be associated with the modulation of cardiac MMP activation, which may be potentially beneficial in the attenuation of post-infarction LV remodelling.
Life and death decisions of the pancreatic β-cell: the role of fatty acids
Authors: Newsholme Philip , Keane Deirdre , Welters Hannah J. , Morgan Noel G.
Published: March 2007

Both stimulatory and detrimental effects of NEFAs (non-esterified fatty acids) on pancreatic β-cells have been recognized. Acute exposure of the pancreatic β-cell to high glucose concentrations and/or saturated NEFAs results in a substantial increase in insulin release, whereas chronic exposure results in desensitization and suppression of secretion, followed by induction of apoptosis. Some unsaturated NEFAs also promote insulin release acutely, but they are less toxic to β-cells during chronic exposure and can even exert positive protective effects. Therefore changes in the levels of NEFAs are likely to be important for the regulation of β-cell function and viability under physiological conditions. In addition, the switching between endogenous fatty acid synthesis or oxidation in the β-cell, together with alterations in neutral lipid accumulation, may have critical implications for β-cell function and integrity. Long-chain acyl-CoA (formed from either endogenously synthesized or exogenous fatty acids) controls several aspects of β-cell function, including activation of specific isoenzymes of PKC (protein kinase C), modulation of ion channels, protein acylation, ceramide formation and/or NO-mediated apoptosis, and transcription factor activity. In this review, we describe the effects of exogenous and endogenous fatty acids on β-cell metabolism and gene and protein expression, and have explored the outcomes with respect to insulin secretion and β-cell integrity.
Inflammatory cytokines, behaviour and age as determinants of self-rated health in women
Authors: Undén Anna-Lena , Andréasson Anna , Elofsson Stig , Brismar Kerstin , Mathsson Linda , Rönnelid Johan , Lekander Mats
Published: March 2007

Self-rated health is a powerful and independent predictor of long-term health, but its biological basis is unknown. We have shown previously that self-rated health is associated with increased levels of circulating cytokines in women. The main aim of the present study was to increase the understanding of the association between markers of wellbeing, such as self-rated health, and cytokines and to investigate the impact of age on these associations. In 174 female consecutive primary health care patients divided into three age groups, we examined subjective ratings of health and aspects of wellbeing and circulating levels of IL (interleukin)-1β, IL-1ra (IL-1 receptor antagonist), IL-6 and TNF-α (tumour necrosis factor-α). Poor self-rated health was significantly associated with higher levels of TNF-α in all of the age groups. For IL-1β and IL-1ra, the correlations with self-rated health were significant only in the oldest age group. Lower ratings of other measurements of health and wellbeing were related to higher levels of cytokines, most pronounced for TNF-α and IL-1β, and in the middle and olderst age groups. More symptoms resembling a sickness response induced by inflammation were implicated to be associated with lower self-rated health. The strength of the association between inflammatory cytokines and poor health perception increased with advanced age, indicating an increased vulnerability for inflammatory activity during aging. It is suggested that higher levels of TNF-α are connected to a sickness response that, in turn, is connected to self-rated health. The results provide a possible psychobiological basis to understand better diffuse subjective symptoms and poor subjective health in women.
The podocyte in health and disease: insights from the mouse
Authors: Michaud Jean-Louis R. , Kennedy Chris R. J.
Published: March 2007

The glomerular filtration barrier consists of the fenestrated endothelium, the glomerular basement membrane and the terminally differentiated visceral epithelial cells known as podocytes. It is now widely accepted that damage to, or originating within, the podocytes is a key event that initiates progression towards sclerosis in many glomerular diseases. A wide variety of strategies have been employed by investigators from many scientific disciplines to study the podocyte. Although invaluable insights have accrued from conventional approaches, including cell culture and biochemical-based methods, many renal researchers continue to rely upon the mouse to address the form and function of the podocyte. This review summarizes how genetic manipulation in the mouse has advanced our understanding of the podocyte in relation to the maintenance of the glomerular filtration barrier in health and disease.
Chronic administration of genistein improves endothelial dysfunction in spontaneously hypertensive rats: involvement of eNOS, caveolin and calmodulin expression and NADPH oxidase activity
Authors: Vera Rocio , Sánchez Manuel , Galisteo Milagros , Villar Inmaculada Concepcion , Jimenez Rosario , Zarzuelo Antonio , Pérez-Vizcaíno Francisco , Duarte Juan
Published: March 2007

The soya-derived phytoestrogen genistein has been suggested to be protective in cardiovascular diseases. In the present study, we have analysed whether chronic oral genistein might influence endothelial function in male SHRs (spontaneously hypertensive rats) via ERs (oestrogen receptors), changes in eNOS (endothelial NO synthase) activity and vascular O2− (superoxide) production. Rats (23-weeks old) were divided into the following groups: WKY (Wistar–Kyoto)-vehicle, SHR-vehicle, WKY-genistein (10 mg·kg−1 of body weight·day−1); SHR-genistein; SHR-genistein-faslodex (ICI 182780; 2.5 mg·kg−1 of body weight·day−1). Vascular expression of eNOS, caveolin-1 and calmodulin-1 were analysed by Western blotting, eNOS activity by conversion of [3H]arginine into L-[3H]citrulline and O2− production by chemoluminescence of lucigenin. In SHRs, after 5 weeks of treatment, genistein reduced systolic blood pressure and enhanced endothelium-dependent aortic relaxation to acetylcholine, but had no effect on the vasodilator responses to sodium nitroprusside. Compared with WKY rats, SHRs had up-regulated eNOS and down-regulated caveolin-1 and calmodulin-1 expression, increased NADPH-induced O2− production, but reduced eNOS activity. Genistein increased aortic calmodulin-1 protein abundance and eNOS activity, and reduced NADPH-induced O2− production in SHRs. The pure ERα and ERβ antagonist faslodex did not modify any of the changes induced by genistein in SHRs, suggesting that these effects are unrelated to ER stimulation. In conclusion, genistein reduced the elevated blood pressure and endothelial dysfunction in SHRs. This latter effect appears to be related to increased eNOS activity associated with increased calmodulin-1 expression and decreased O2− generation.
Growth hormone decreases phase II ventricular tachyarrhythmias during acute myocardial infarction in rats
Authors: Elaiopoulos Dimitrios A. , Tsalikakis Dimitrios G. , Agelaki Maria G. , Baltogiannis Giannis G. , Mitsi Agathokleia C. , Fotiadis Dimitrios I. , Kolettis Theofilos M.
Published: March 2007

GH (growth hormone) administration during acute MI (myocardial infarction) ameliorates subsequent LV (left ventricular) dysfunction. In the present study, we examined the effects of such treatment on arrhythmogenesis. A total of 53 Wistar rats (218±17 g) were randomized into two groups receiving two intraperitoneal injections of either GH (2 international units/kg of body weight; n=26) or normal saline (n=27), given at 24 h and 30 min respectively, prior to MI, which was generated by left coronary artery ligation. A single-lead ECG was recorded for 24 h post-MI, using an implanted telemetry system. Episodes of VT (ventricular tachyarrhythmia) and VF (ventricular fibrillation) during the first hour (phase I) and the hours following (phase II) MI were analysed. Monophasic action potential was recorded from the lateral LV epicardium at baseline and 24 h post-MI, and APD90 (action duration at 90% of repolarization) was measured. Infarct size was calculated 24 h post-MI. Infarct size and phase I VT+VF did not differ significantly between groups, but phase II hourly duration of VT+VF episodes was 82.8±116.6 s/h in the control group and 18.3±41.2 s/h in the GH group (P=0.0027), resulting in a lower arrhythmic (P=0.016) and total (P=0.0018) mortality in GH-treated animals. Compared with baseline, APD90 was prolonged significantly 24 h post-MI in the control group, displaying an increased beat-to-beat variation, but remained unchanged in the GH group. We conclude that GH decreases phase II VTs during MI in the rat. This finding may have implications in cardiac repair strategies.
Induction of apoptosis in rat lymphocytes by starvation
Authors: Pires Juliana , Curi Rui , Otton Rosemari
Published: March 2007

The aim of the present study was to investigate whether fasting for 24 and 48 h induces apoptosis of rat mesenteric lymph node lymphocytes similar to that observed previously in diabetic patients and alloxan-induced diabetic rats. Several features of lymphocyte death were evaluated by flow cytometry. Plasma levels of glucose, NEFAs (non-esterified fatty acids) and ketone bodies (acetoacetate and β-hydroxybutyrate) were determined in rats fasted for 24 and 48 h. Lymphocytes obtained from fasted rats had an increase in DNA fragmentation and phosphatidylserine externalization after 48 h of culture, although there was no loss of membrane integrity in lymphocytes even after 48 h of culture. Cytochrome c release from the mitochondrial intermembrane space into the cytosol was increased significantly in lymphocytes from fasted rats cultured for 24 h, whereas the levels of bcl-2 and bax proteins were not affected. Activities of caspases 3, 6, 8 and 9 were increased significantly in lymphocytes from rats fasted for 24 h, whereas only an increase in caspase 3 and 9 activities were observed in rats fasted for 48 h. In conclusion, fasting for 24 and 48 h caused a significant increase in the proportion of lymphocytes undergoing apoptosis. The occurrence of apoptosis was observed by DNA fragmentation, phosphatidylserine externalization, cytochrome c release from the mitochondria and activation of the caspase cascade. These findings support the hypothesis that conditions that raise plasma fatty acids levels (e.g. diabetes and starvation) may impair immune function by causing lymphocyte death.
Altered calcium signalling in platelets from bile-duct-ligated rats
Authors: Atucha Noemí M. , Iyú David , Alcaraz Antonia , Rosa Vladimir , Martínez-Prieto Concepción , Ortiz M. Clara , Rosado Juan Antonio , García-Estañ Joaquín
Published: March 2007

In the present study, we have analysed the mechanisms of Ca2+ entry and release in platelets obtained from BDL (bile-duct-ligated) rats, 11–13 days and 4 weeks after surgery. Platelets were washed and loaded with fura-2, and [Ca2+]i (cytosolic Ca2+ concentration) was determined in cell suspensions by means of fluorescence spectroscopy. Basal [Ca2+]i was similar in platelets from BDL rats compared with those from their respective controls, both in the absence and presence of extracellular Ca2+. Platelet stimulation with thrombin in the absence and presence of extracellular Ca2+ induced a rapid rise in [Ca2+]i that was of greater magnitude in platelets from BDL rats than in controls. Ca2+ storage was significantly elevated in platelets from BDL rats, as well as the activity of SERCA (sarcoplasmic/endoplasmic-reticulum Ca2+-ATPase). Capacitative Ca2+ entry, as evaluated by inhibition of SERCA with thapsigargin, was also altered in platelets from BDL rats, having lower rates of Ca2+ entry. In conclusion, chronic BDL alters intracellular Ca2+ homoeostasis in platelets, such that an enhanced Ca2+ release is evoked by thrombin, which may be due to an increased amount of Ca2+ stored in the intracellular organelles and secondary to an enhanced activity of SERCA. These alterations are already evident before cirrhosis has completely developed and occurs during the cholestasis phase.
AT1 receptor blockade prevents the decrease in conduit artery flow-mediated dilatation during NOS inhibition in humans
Authors: Bellien Jeremy , Iacob Michele , Eltchaninoff Helene , Bourkaib Ryad , Thuillez Christian , Joannides Robinson
Published: March 2007

Whether AT1 (angiotenin II type 1) receptor blockade can prevent the decrease in conduit artery FMD (flow-mediated dilatation) during NOS (nitric oxide synthase) inhibition by alternative endothelial pathways has not been explored previously in humans. In 12 healthy subjects, we measured radial artery diameter (echotracking) and flow (Doppler) during FMD induced by sustained reactive hyperaemia during a control period and following NOS inhibition [1.5 mg·min−1·l−1L-NMMA (NG-monomethyl-L-arginine)], after a single oral administration of telmisartan (80 mg) or placebo, using a randomized double-blind cross-over design. In six volunteers, we also assessed the roles of prostacyclin and EDHF (endothelium-derived hyperpolarizing factor) during radial FMD after AT1 receptor blockade by oral administration of aspirin (500 mg) alone, aspirin+L-NMMA or aspirin+L-NMMA+fluconazole (a cytochrome epoxygenases inhibitor; 0.37 mg·min−1·l−1). Telmisartan did not affect radial artery FMD in the control period (10.9±0.6% with placebo compared with 9.9±0.7% with telmisartan), but prevented its decrease after L-NMMA (9.3±0.8% with placebo compared with 12.6±1.2% with telmisartan; P<0.05) with no modification in baseline parameters, hyperaemia and radial artery endothelium-independent dilatation to sodium nitroprusside. Moreover, in telmisartan-treated subjects, radial artery FMD, compared with control (9.0±1.0%), was not modified by aspirin alone (9.4±0.7%) or associated with L-NMMA (9.5±0.5%), but was reduced by the combination of aspirin, L-NMMA and fluconazole (7.5±0.6%; P<0.05). These results demonstrate that AT1 receptor blockade prevents the decrease in conduit artery FMD during NOS inhibition in humans, suggesting the development of a compensatory endothelial mechanism. This mechanism appears to be independent of prostacyclin and could possibly be related to an EDHF release.
Leukotriene B4 production in healthy subjects carrying variants of the arachidonate 5-lipoxygenase-activating protein gene associated with a risk of myocardial infarction
Authors: Maznyczka Annette , Mangino Massimo , Whittaker Andrew , Braund Peter , Palmer Tom , Tobin Martin , Goodall Alison H. , Bradding Peter , Samani Nilesh J.
Published: March 2007

Leukotrienes are implicated in the pathogenesis of coronary artery disease. Recently two haplotypes (HapA and HapB) in the gene encoding ALOX5AP (arachidonate 5-lipoxygenase-activating protein), the main regulator of 5-lipoxygenase, have been associated with a doubling of the risk of myocardial infarction. Studies have also shown that treatment with a leukotriene inhibitor reduces biomarkers of coronary risk in patients carrying HapA, raising the possibility of developing genotype-specific therapy. In the present study, we examined whether carriage of HapA or HapB is associated with increased LTB4 (leukotriene B4) production in healthy subjects. Age- and gender-matched healthy HapA carriers (n=21), HapB carriers (n=20) and non-A/non-B carriers (n=18), with no reported history of cardiovascular disease, were recruited following DNA screening of 1268 subjects from a population-based study. Blood neutrophils were isolated, and LTB4 production was measured in response to stimulation with 1 μmol/l of the calcium ionophore A23187. There was no difference in the mean level for LTB4 production in the three groups (non-A/non-B, 24.9±8.3 ng/106 cells; HapA, 22.2±11.9 ng/106 cells; HapB, 19.8±4.8 ng/106; P=0.14). The findings indicate that if either the HapA or the HapB haplotype of ALOX5AP indeed increases cardiovascular risk, then the mechanism is not simply due to a systematically observable effect of the haplotype on LTB4 production in response to stimulation. The results suggest that knowledge of a patient's haplotype may not provide useful information on the probable clinical response to ALOX5AP inhibitors.
Effects of glucagon-like peptide-1-(7–36)-amide on pancreatic islet and intestinal blood perfusion in Wistar rats and diabetic GK rats
Authors: Svensson Annika M. , Östenson Claes-Göran , Efendic Suad , Jansson Leif
Published: March 2007

The aim of the present study was to evaluate the effects of GLP-1 [glucagon-like peptide-1-(7–36)-amide] on total pancreatic, islet and intestinal blood perfusion in spontaneously hyperglycaemic GK rats and normal Wistar rats using a microsphere technique. GK rats had hyperglycaemia and increased pancreatic and islet blood flow. Blood glucose concentrations were not affected when measured shortly (8 min) after GLP-1 administration in either GK or Wistar rats. GLP-1 had no effects on baseline pancreatic or islet blood flow in Wistar rats, but did prevent the blood flow increase normally seen following glucose administration to these animals. In GK rats, administration of GLP-1 decreased both pancreatic and islet blood flow. Glucose administration to the GK rats decreased pancreatic and islet blood flow. This decrease was not affected by pre-treatment with GLP-1. We conclude that administration of GLP-1 leads to a decrease in the augmented blood flow seen in islets of diabetic GK rats. The GLP-1-induced action on islet blood perfusion may modulate output of islet hormones and contribute to the antidiabetogenic effects of the drug in Type 2 diabetes (non-insulin-dependent diabetes).
Gender-related differences in the sympathetic vasoconstrictor drive of normal subjects
Authors: Hogarth Andrew J. , Mackintosh Alan F. , Mary David A. S. G.
Published: March 2007

The risk of cardiovascular disease has been linked to sympathetic activation and its incidence is known to be lower in women than in men. However, the effect of gender on the sympathetic vasoconstrictor drive has not yet been established. In the present study, we investigated whether there is a gender difference in MSNA (muscle sympathetic nerve activity) and blood flow, and to determine the mechanisms involved. We examined 68 normal subjects, 34 women and 34 men, matched for age, BMI (body mass index) and waist circumference. MSNA was measured as the mean frequency of single units (s-MSNA) and as multi-unit bursts (m-MSNA) from the peroneal nerve simultaneously with its supplied muscle CBF (calf blood flow). Women had lower (P=0.0007) s-MSNA (24±2.0 impulses/100 cardiac beats) than men (34±2.3 impulses/100 cardiac beats), and a greater baroreceptor reflex sensitivity controlling efferent sympathetic nerve activity than men. The sympathetic activity was inversely and directly correlated respectively, with CBF (P=0.03) and CVR (calf vascular resistance; P=0.01) in men only. The responses of an increase in CVR to cold pressor and isometric handgrip tests were significantly smaller in women (P=0.002) than in men, despite similar increases in efferent sympathetic nerve activity. Women had a lower central sympathetic neural output to the periphery, the mechanism of which involved differences in central and reflex control, as well as a lower vasoconstrictor response to this neural output. It is suggested that this may partly explain the observed lower incidence of cardiovascular events in women compared with men.
Structural and dielectric properties of Ta-modified Pb(Sc0.5Nb0.5)O3 ceramics
Authors: Correa Margarita , Choudhary R. N. P. , Katiyar R. S.
Published: March 2007

The polycrystalline (with nanosized particles) samples of Pb(Sc0.5Nb(1−x)∕2Tax∕2)O3 (PSNT) (x=0, 0.3, 0.5, 0.7, and 1) were prepared using mechanical activation system and the mixed oxide routes. The compounds were found in rhombohedral structure with the presence of a small amount of pyrochlore phase. The changes in the microstructures were observed on increasing Ta contents in PSNT. Studies of dielectric properties as a function of temperature (200–600K) and frequency (1kHz–1MHz) of the sintered samples of different compositions have enabled us to determine the phase transition behavior of relaxor type with the diffuse phase transition for x⩽0.3. For higher values of x (⩾0.5) the diffuse phase transition suggested nonrelaxor type of phase transition in PSNT. The changes in the dielectric/relaxor properties of the compounds are compositional and sintering temperature dependent. The room temperature Raman measurement confirmed the presence of nanosized regions, diffuse phase transition, and relaxor ferroelectric characteristic of PSNT.
Behavior of bending motion of polyurethane film with carbon nanofiber as electrode
Authors: Hirai Toshihiro , Islam Mohammad Hamidal , Takasaki Midori , Watanabe Masashi
Published: March 2007

The behavior of bending motion by an electric field for a polyurethane elastomer (PUE) film for which vapor grown carbon fiber (VGCF) was used as an electrode was examined. When the electric field was applied to the PUE film with the VGCF electrode, it bent towards the cathode side. In the case wherein the PUE film was doped with sodium acetate, it was observed that the bending displacement of the PUE film with the VGCF electrode was larger than for the undoped PUE film. The absolute value of the charge current was similar to that of the discharge current in doped PUE film with the VGCF electrode and this result corresponds to less leakage current. Highly efficient charge holding was also observed in the doped PUE film with the VGCF electrode, since the steady current by applying an electric field was less than 0.1μA.
Compensation mechanism in high purity semi-insulating 4H-SiC
Authors: Mitchel W. C. , Mitchell William D. , Smith H. E. , Landis G. , Smith S. R. , Glaser E. R.
Published: March 2007

A study of deep levels in high purity semi-insulating 4H-SiC has been made using temperature dependent Hall effect (TDH), thermal and optical admittance spectroscopies, and secondary ion mass spectrometry (SIMS). Thermal activation energies from TDH varied from a low of 0.55eV to a high of 1.65eV. All samples studied showed n-type conduction with the Fermi level in the upper half of the band gap. Fits of the TDH data to different charge balance equations and comparison of the fitting results with SIMS measurements indicated that the deep levels are acceptorlike even though they are in the upper half of the band gap. Carrier concentration measurements indicated that the deep levels are present in concentrations in the low 1015cm−3 range, while SIMS results demonstrate nitrogen and boron concentrations in the low to mid-1015-cm−3 range. The results suggest that compensation in this material is a complex process involving multiple deep levels.
CoFe-based amorphous alloy with high relaxation frequency
Authors: Betancourt I. , Vazquez F.
Published: March 2007

Amorphous Co43Fe20B31.5Ta5.5 ribbons prepared by melt-spinning technique, showed a relaxation frequency fx of 3MHz, higher than any other known amorphous alloy. Additional complex permeability measurements reflected the reversible bulging of domain walls as the active magnetization mechanism below fx. The magnetoimpedance (MI) effect was also detected for this alloy, with a maximum variation of 1.6% at 5MHz. A positive saturation magnetostriction of 0.085×10−6 was estimated from tension-stress–MI measurements.
Ultraviolet emission and Fano resonance in doped nano-alumina
Authors: Li Bin , Oliveira Samuel L. , Rand Stephen C. , Azurdia Jose A. , Hinklin Tom R. , Marchal Julien C. , Laine Richard M.
Published: March 2007

Emission properties of Al2O3 nanopowders, synthesized by flame spray pyrolysis with Mg, Cr, and Sc dopants, are investigated, principally in the protein lysing range of 250–290nm (UV-C band). As expected, point defect densities depend on crystal phase and irradiation history and strongly influence emission properties at short wavelengths. Ultraviolet and visible emission intensities of aggregated point defect centers change upon electron beam exposure at high current densities, but ultraviolet emission from point defects is persistently enhanced over a narrow range of Mg-doped Al2O3 compositions slightly off spinel stoichiometry. At 40% Mg concentration, emission intensities at 320nm rise by over an order of magnitude after beam exposure. Quantum efficiency for cathodoluminescence in the 250–300nm range nevertheless remains low. Point defect ionization at high currents shifts the emission of Al2O3 nanopowders to the infrared and is shown to be correlated with a ubiquitous Fano resonance in ionized Cr-vacancy complexes. This base line spectroscopy permits us to attribute the very high quantum efficiency of UV-C luminescence in annealed Sc3+:Al2O3 primarily to the formation of α-phase Al2O3.
Dielectric behaviors of Pb(Fe2∕3W1∕3)-PbTiO3 relaxors: Models comparison and numerical calculations
Authors: Hong Cheng-Shong , Chu Sheng-Yuan , Su Wen-Chang , Chang Ren-Chuan , Nien Hsiau-Hsian , Juang Yung-Der
Published: March 2007

Regarding the dielectric characteristics of the diffusion phase transition (DPT) in ferroelectric relaxor materials, several researchers have provided similar but different laws to explain these phenomenon. These laws, presented by Burfoot et al. and Eiras et al., have been proven to provide a better explanation, especially the dielectric diffusion phenomenon, of the incomplete DPT materials if compared with the models presented by Smolensky, and Isupov. However, the differences in fitting adaptability and the physical and mathematical meanings between these two laws have never been discussed. In this paper, we analyze these two laws in the (1−x)Pb(Fe2∕3W1∕3)-xPbTiO3 [(1−x)PFW-xPT] relaxor system using the statistical regression theory. We find that the laws of both Burfoot and Eiras demonstrate the same adaptability and provide smaller estimation bias on the samples than the models of Smolensky and Isupov, despite the complete or incomplete DPT characteristics. When x is smaller, the samples tend to be complete DPT phenomenon and the estimation bias of Smolensky and Isupov`s models is relatively smaller. However, when the samples show ferroelectric characteristics, the estimation bias will be increased.
Magnetic and magnetocaloric properties of Cu-substituted La1−xPbxMnO3 (x∼0.14) single crystals
Authors: Zhao B. C. , Sun Y. P. , Zhu X. B. , Song W. H.
Published: March 2007

Structural, magnetic, and magnetocaloric properties in perovskite manganites La1−xPbxMn1−y−zCuyO3 (x~0.14, y=0, 0.01, 0.02, z=0.02, 0.08, 0.11) single crystals have been investigated. The Curie temperature TC decreases monotonously with increasing Cu-doping concentration. A sharp downturn in the inverse magnetic susceptibility 1/χm vs T plot at Griffiths temperature TG well above TC was observed for the free-doped sample, which can be attributed to the appearance of spin cluster in the paramagnetic state. The temperature interval between TG and TC decreases with increasing Cu-doping level and almost disappears as Cu concentration reaches 0.02. Large magnetic entropy change ΔSM occurs near TC and ΔSM approaches a maximum value for the sample with Cu-doping level y=0.01. The result can be explained based on the competing effect between the double-exchange interaction and the lattice distortion induced by Cu doping.
Decay of zone-center phonons in GaN with A1, E1, and E2 symmetries
Authors: Song D. Y. , Nikishin S. A. , Holtz M. , Soukhoveev V. , Usikov A. , Dmitriev V.
Published: March 2007

We report Raman studies of the A1(TO), E1(TO), E22, A1(LO), and E1(LO) symmetry phonons of GaN from 20to325K. By applying anharmonic decay theory to the observed temperature dependences of the phonon energies and linewidths, we determine the phonon decay mechanisms of these zone-center vibrations. Thermal expansion is taken into account using published temperature-dependent coefficients. The A1(TO) and E1(TO) vibrations are described by symmetric two-phonon decay. The E22 decays via the creation of three phonons. Both A1(LO) and E1(LO) bands are interpreted by an asymmetric two-phonon decay, with a minor contribution to the decay of the former from the three-phonon creation. Phonon lifetimes are obtained based on the observed linewidths.
Lateral field excitation of thickness shear mode waves in a thin film ZnO solidly mounted resonator
Authors: Corso Christopher D. , Dickherber Anthony , Hunt William D.
Published: March 2007

In recent years, interest in the development of highly sensitive acoustic wave devices as biosensor platforms has grown. A considerable amount of research has been conducted on AT-cut quartz resonators both in thickness excitation and in lateral excitation configurations. In this report, we demonstrate the fabrication of a ZnO solidly mounted resonator operated in thickness shear mode (TSM) using lateral field excitation of the piezoelectric film. Theoretical Christoffel equation calculations are provided to explore the conditions for excitation of a TSM wave in c-axis-oriented ZnO through lateral excitation. The existence of a TSM wave is verified through the comparison of theoretical and experimentally obtained acoustic velocity values from frequency versus thickness measurements and water loading of the resonators. A major strength of this design is that it incorporates a simple eight-layer, single-mask fabrication process compatible with existing integrated circuit fabrication processes and can be easily incorporated into multidevice arrays. With minimal electrode optimization, we have been able to fabricate resonators with nearly 100% yield that demonstrate Q values of up to 550 and K2 values of 0.88% from testing of more than 30 devices.
Ferroelectrets with improved thermal stability made from fused fluorocarbon layers
Authors: Zhang X. , Hillenbrand J. , Sessler G. M.
Published: March 2007

Several layers of polytetrafluoroethylene and fluoroethylenepropylene films are fused such that small interfacial gas voids are formed between the layers. After proper charging and annealing, the fused multilayer films show large and thermally stable quasistatic piezoelectric d33 coefficients of about 1000pC∕N which are subject to a minor reduction of 3% per day if exposed to 90°C. Depending on sample processing, the piezoelectric coefficient is relatively independent of applied pressure in the range up to 20kPa and of applied frequency up to about 100kHz. Thermally-stimulated discharge measurements indicate that the decay of the piezoelectric activity at higher temperatures is at least partially due to charge drift along the surfaces of the voids. A microphone built with the cellular ferroelectrets has a sensitivity of 3mV∕Pa at 1kHz.
Stress-induced anisotropy of graphitelike amorphous carbon
Authors: Zollner Stefan , Qin Wentao , Gregory Richard B. , Edwards N. V. , Junker Kurt , Tiwald Thomas E.
Published: March 2007

Ellipsometry spectra of graphitelike amorphous carbon films on Si reveal a strong anisotropy of the optical constants in the 0.7–9.5eV photon-energy range. The films are optically uniaxial, with the optical axis oriented normal to the surface. This birefringence can be explained by ordering of the hexagonal graphene planes perpendicular to the substrate due to tensile stress, which was confirmed by transmission electron microscopy. All films show two peaks in the optical absorption, corresponding to the ordinary and extraordinary absorption peaks in graphite.
General excitations in time-dependent density functional theory
Authors: Vahtras Olav , Rinkevicius Zilvinas
Published: March 2007

A general framework within time-dependent density functional theory is presented for the calculation of excitations to states of arbitrary multiplicity in molecular systems with a non-singlet ground state. The proposed approach combines generalized orbital excitation operators designed to generate excited states which have well-defined multiplicities and the noncollinear formulation of density functional theory and it can be straightforwardly implemented in currently existing density functional programs.
Surface nucleation of the (111) plane of excimer laser annealed Si on SiO2 substrates: A molecular dynamics study
Authors: Lee Byoung Min , Kuranaga Takahide , Munetoh Shinji , Motooka Teruaki
Published: March 2007

We have investigated the nucleation and crystallization processes of molten silicon (Si) on SiO2 substrates by performing molecular dynamics (MD) simulations based on the modified Tersoff potential parameters. A heat flow that leads to a steady fall of the local temperature in the molten Si is achieved by determining the atomic movements with the combination of Langevin and Newton equations. Good agreement is reached between the predictions of temperatures based on the kinetic energies and the velocity distributions of atoms at local regions. The results of simulations revealed that the (111) plane of the Si nuclei formed at the surface was predominantly parallel to the substrate of MD cell. The surface energies of the (100), (110), and (111) planes of Si at 77 K were calculated to be 2.27, 1.52, and 1.20 J∕m2, respectively, and they were in good agreement with the experimental results. The lowest value of surface energy, 1.20 J∕m2, for the (111) plane at 1700 K was obtained under the condition of elastic hard wall. The surface energy anisotropy is expected to be a driving force for the preferential surface nucleation of Si(111) at the surface.
Thermal conductivity modeling of compacted nanowire composites
Authors: Tian Weixue , Yang Ronggui
Published: March 2007

Nanocomposites may realize a similar thermal conductivity reduction and thermoelectric efficiency enhancement observed in superlattices and thus provide a pathway to scale up the benefits of the nanoscale effects to thermoelectric materials in bulk form. If there are two species, nanocomposites can be in the form of nanoparticles or nanowires of one material specie embedded in another host matrix material, or a discrete mixture of two different kinds of nanoparticles/nanowires that are compacted. A nanocomposite in the form of discrete mixtures of nanowires/nanoparticles does not have a continuous phase of material and may yield even lower thermal conductivity than composites with nanowires/nanoparticles embedded in a host material at the same stoichiometry. In this paper, phonon transport in compacted nanowire composites is investigated using the Monte Carlo simulation. Results show that the thermal conductivity of composites in the form of compacted silicon and germanium nanowire mixtures can be further reduced to around half of the previously studied composites with silicon nanowires embedded in a germanium matrix at the same atomic composition and characteristic size of the nanowires.
Rotator and extender ferroelectrics: Importance of the shear coefficient to the piezoelectric properties of domain-engineered crystals and ceramics
Authors: Davis Matthew , Budimir Marko , Damjanovic Dragan , Setter Nava
Published: March 2007

The importance of a high shear coefficient d15 (or d24) to the piezoelectric properties of domain-engineered and polycrystalline ferroelectrics is discussed. The extent of polarization rotation, as a mechanism of piezoelectric response, is directly correlated to the shear coefficient. The terms “rotator” and “extender” are introduced to distinguish the contrasting behaviors of crystals such as 4mm BaTiO3 and PbTiO3. In rotator ferroelectrics, where d15 is high relative to the longitudinal coefficient d33, polarization rotation is the dominant mechanism of piezoelectric response; the maximum longitudinal piezoelectric response is found away from the polar axis. In extender ferroelectrics, d15 is low and the collinear effect dominates; the maximum piezoelectric response is found along the polar axis. A variety of 3m, mm2, and 4mm ferroelectrics, with various crystal structures based on oxygen octahedra, are classified in this way. It is shown that the largest piezoelectric anisotropies d15∕d33 are always found in 3m crystals; this is a result of the intrinsic electrostrictive anisotropy of the constituent oxygen octahedra. Finally, for a given symmetry, the piezoelectric anisotropy increases close to ferroelectric-ferroelectric phase transitions; this includes morphotropic phase boundaries and temperature induced polymorphic transitions.
Temperature dependence of the yttria-stabilized zirconia Raman spectrum
Authors: Lughi Vanni , Clarke David R.
Published: March 2007

The Raman spectrum of 5wt% yttria-stabilized tetragonal zirconia from 25to1250°C is reported. All six Raman bands broaden and shift toward lower energy with increasing temperature. The shift associated with thermally induced volume changes is shown to be the main contribution for all bands, but does not explain the unexpected negative value of the thermospectroscopic coefficient found for the mode at 260cm−1 (at room temperature). For all bands, the shift is found to be quasilinear in the range of temperatures considered. As the thermospectroscopic coefficients are large, Raman spectroscopy is well suited as a noncontact, in situ method for monitoring temperature in applications of yttria-stabilized zirconia such as thermal barrier coatings and fuel cells.
Shock wave compression of the ferroelectric ceramic Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3: Microstructural effects
Authors: Setchell Robert E.
Published: March 2007

Shock wave compression of poled Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 results in rapid depoling and release of bound charge. Different porous microstructures can be produced in the material by adding different types and amounts of organic pore formers prior to bisque firing and sintering. In previous studies, extensive planar-impact experiments on a baseline material having a fixed porous microstructure were conducted to determine Hugoniot states, to examine constitutive mechanical properties during shock propagation, and to investigate shock-induced depoling characteristics. Additional comparative experiments were conducted to investigate the effects of a different porous microstructure in a material having the same density, and also the effects of different initial densities. These comparisons indicated that differences in the porous microstructure of common-density materials have little effect on mechanical and electrical shock properties, in contrast to large effects observed when initial density is varied. To examine microstructural effects more extensively in the present study, additional common-density materials having distinctly different microstructures were prepared. Each material was made using spherical pore formers having diameters within a narrow range, with the mean diameter varying over a broad range between the different materials. Normally poled samples of each material were subjected to two particular experimental conditions that had proved useful for revealing important depoling and yielding properties in the baseline material. Results from materials made with larger pore formers again indicated that shock properties are insensitive to microstructural differences in common-density materials. Materials made with the smallest pore formers were an important exception, with the most noticeable difference being a significantly higher threshold for dynamic yielding.
Relaxation property of the magnetic-fluid-based fiber-optic evanescent field modulator
Authors: Pu Shengli , Chen Xianfeng , Di Ziyun , Xia Yuxing
Published: March 2007

The details about the modulation property of the magnetic-fluid-based fiber-optic evanescent field modulator are studied in this article. Experiments show that it needs some time for the outgoing light from the modulator to reach the final steady value when the external magnetic field is turned on or off (called the relaxation property of the modulator). Two exponential functions are employed to fit the experimental data of the falling and rising relaxation processes in order to achieve the falling and rising response times. By this method, the magnetic field dependent falling and rising response times are gained. The physical mechanisms of the relaxation property of the modulator are discussed qualitatively.
Excited state radiationless decay process with Duschinsky rotation effect: Formalism and implementation
Authors: Peng Qian , Yi Yuanping , Shuai Zhigang , Shao Jiushu
Published: March 2007

Duschinsky rotation effect is a simple and effective way to characterize the difference between the ground state and excited state potential energy surfaces. For complex molecules, harmonic oscillator model is still the practical way to describe the dynamics of excited states. Based on the first-order perturbation theory à la Fermi golden rule, the authors have applied the path integral of Gaussian type for the correlation function to derive an analytic formalism to calculate the internal conversion rate process with Duschinsky rotation effect being taken into account. The validity of their formalism is verified through comparison with previous work, both analytically for the case of neglecting Duschinsky rotation and numerically for the ethylene molecules with two-mode mixing. Their expression is derived for multimode mixing.