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1

Digitale Medien

Surface photovoltage spectroscopy and normal-incidence reflectivity characterization of a 1.3 μm InGaAlAs/InP vertical-cavity surface-emitting laser structure (2002)

Huang, Y. S. ; Malikova, L. ; Pollak, Fred H.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 91 (2002), S. 6203-6205

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We have investigated a 1.3 μm InGaAlAs/InP (001) vertical-cavity surface-emitting laser (VCSEL) structure using surface photovoltage spectroscopy (SPS) and normal-incidence reflectivity. The SPS measurements were performed as a function of angle of incidence relative to the normal (0°–55°) and temperature (300 K〈T〈420 K). The SPS spectra exhibit both the fundamental conduction to heavy-hole excitonic transition and cavity mode plus a rich interference pattern related to the mirror stack. The advantages of SPS in relation to other methods to study VCSELs, such as photoreflectance and photocurrent spectroscopy, are discussed. This experiment demonstrates the considerable potential of SPS for the characterization of these device structures. © 2002 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1467396

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Digitale Medien

Polarized-photoreflectance characterization of an InGaP/InGaAsN/GaAs NpN double-heterojunction bipolar transistor structure (2001)

Lin, C. J. ; Huang, Y. S.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 90 (2001), S. 4565-4569

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We have characterized an InGaP/InGaAsN/GaAs NpN double-heterojunction bipolar transistor structure using polarized photoreflectance (PR) spectroscopy. The ordering parameter of the InGaP is deduced from the polarization {[110] and [11¯0]} dependence of the PR signals from the emitter region. The ordering related piezoelectric field is also found to influence the electric field, as evaluated from observed Franz–Keldysh oscillations, in the InGaP emitter region. The field in the emitter region is found to be about 25 kV/cm smaller than the theoretical value that does not take into account the possible ordering induced screening effect, while the field in the collector region agrees well with the theoretical value. In addition, the InGaAsN band gap is also determined by analyzing the PR spectrum of the base region. © 2001 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1405823

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3

Digitale Medien

Identification of the switching field function in vector hysteresis models (2000)

Huang, Y. ; Friedman, G.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 87 (2000), S. 4777-4779

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: This article deals with a large class of magnetic hysteresis models where bistable elements are the basis of hysteretic behavior. The switching field function characterizes the curves that have to be crossed by the magnetic field vector in order for the bistable elements to switch. This article reports experiments that use observations of the aggregate magnetization to identify the switching field function of the bistable elements in two dimensions. © 2000 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.373156

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4

Digitale Medien

CoPt and FePt thin films for high density recording media (2000)

Christodoulides, J. A. ; Huang, Y. ; Zhang, Y. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 87 (2000), S. 6938-6940

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Highly anisotropic face-centered-tetragonal (fct) CoPt and fct FePt nanoparticles have been prepared and embedded in a C or BN matrix by cosputtering from pure Co50Pt50, BN, and Fe50Pt50, C solid targets using a tandem deposition mode. The as-made films show a disordered face-centered-cubic structure which is magnetically soft and have low coercivity (〈20 Oe). Magnetic hardening occurs after heat treatment at elevated temperatures, which leads to increase in coercivity to values up to 15 kOe at room temperature. The hardening is due to the formation of nanoparticles with the highly anisotropic fct with anisotropy K〉107 erg/cm3. Transmission electron microscope studies showed FePt particles embedded in C matrix with a size increasing from below 3 nm in the as-made state to about 8 nm in the optimum annealed state. These results are very promising and make these materials potential candidates for high-density magnetic recording. © 2000 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.372892

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5

Digitale Medien

Room temperature polarized photoreflectance characterization of GaAlAs/InGaAs/GaAs high electron mobility transistor structures including the influence of strain relaxation (2000)

Chen, T. H. ; Huang, Y. S.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 88 (2000), S. 883-888

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Using room temperature photoreflectance (PR) we have characterized the properties of three GaAlAs/InGaAs/GaAs high electron mobility transistor structures with two different well widths fabricated by molecular beam epitaxy on (001) GaAs substrates. The samples were denoted as #1, #2, and #3 with well widths of 140, 160, and 160 Å, respectively. Samples #2 and #3 were grown on substrates with different threading dislocation densities. For the latter two samples the well width exceeds the pseudomorphic limit so that there are some strain relaxation and related misfit dislocations as determined from the x-ray measurements. In order to detect the anisotropic strain of the misfit dislocations related to strain relaxation, the PR measurements were performed for incident light polarized along [110] and [11¯0] directions. Evidence for the influence of the strain relaxation upon the relaxed channel was provided by the observed anisotropy of the polarized PR signal in the InGaAs channel layer. Signals have been observed from every region of the sample, making it possible to evaluate the In and Al compositions, channel width and two-dimensional electron gas density, as well as the properties of the GaAs/GaAlAs multiple quantum well buffer layer. © 2000 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.373751

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6

Digitale Medien

Piezoreflectance study of an Fe-containing silicon carbon nitride crystalline film (2000)

Hsieh, C. H. ; Huang, Y. S.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 87 (2000), S. 280-284

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: A detailed piezoreflectance (PzR) study of an Fe-containing silicon carbon nitride crystalline film in the temperature range between 15 and 580 K was performed. From the line shape fit of the PzR spectra, the impurity to band and the direct band-to-band transition energies which are denoted as Ei and Egd, respectively, at various temperatures were accurately determined. The parameters that describe the temperature dependence of Ei and Egd are evaluated and discussed. © 2000 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.371856

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7

Digitale Medien

Short-Term Incubation with Physiological Level of Estrogen Impairs ß1-Adrenoceptor-Mediated but Enhances ß2-Adrenoceptor Mediated Coronary Relaxation (2002)

Chan, HY ; Yao, XQ ; He, GW ; [weitere]

350 Main Street , Malden , MA 02148 , USA. , and 9600 Garsington Road , Oxford OX4 2DQ , England . : Blackwell Science Inc

Journal of cardiac surgery 17 (2002), S. 0

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ISSN: 1540-8191

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Medizin

Notizen: Considerable evidence suggests that ß-adrenoceptors are subject to regulation by sex steroid hormones. It was reported that estrogen replacement potentiated the vascular responses mediated by ß-adrenoceptor activation by an endothelium-independent mechanism. ß-Adrenoceptor is present on both vascular smooth-muscle and endothelial cells. However, no experiment has examined the effect of acute exposure to physiological concentrations of estrogen on ß-adrenoceptor–mediated vasorelaxation in mammalian arteries. The major observation in this study is that the relaxant response to ß2-adrenoceptor activation with fenoterol was significantly enhanced by short-term incubation (1 hr) with 0.3 nM 17ß-estradiol in the isolated porcine coronary circumflex arteries. This effect was abolished by pretreatment with 10-μM tamoxifen. Preincubation with 17ß-estradiol (0.3 nM) reduced the relaxant response to dobutamine, a ß1-adrenoceptor agonist. The concentration of 0.3 nM falls into the reported circulating level of estrogen ranging between 0.1 and 1 nM in the body. Low concentrations of estrogen appeared to slightly enhance the relaxation induced by isoproterenol, a non-selective ß- (ß1 and ß2) adrenoceptor agonist, following 1-hr incubation. Physiological level of estrogen did not influence the relaxation induced by IBMX, an inhibitor of phosphodiesterase. In contrast, 20-min exposure to 17ß-estradiol (0.1–1 nM) was without effect on ß1- or ß2-adrenoceptor-mediated vascular responses. Our data indicate that acute exposure to physiological concentration of estrogen has differential effect on ß-adrenoceptor-mediated relaxation in porcine coronary arteries, increasing ß2-adrenergic response but decreasing ß1-adrenergic response. It would therefore be not surprising to observe a marginal effect of estrogen on relaxation induced by isoproterenol, an agonist that activates both ß1 and ß2-adrenoceptors in blood vessels. (supported by UPGC Direct Grant)

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1540-8191.2002.101416.x

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8

Digitale Medien

Different Effects of Estrogen and Progesterone on K+ Currents Expressed in Xenopus Oocytes (2002)

Wong, CM ; Yao, XQ ; Tsang, SY ; [weitere]

350 Main Street , Malden , MA 02148 , USA. , and 9600 Garsington Road , Oxford OX4 2DQ , England . : Blackwell Science Inc

Journal of cardiac surgery 17 (2002), S. 0

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ISSN: 1540-8191

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Medizin

Notizen: Potassium channel plays an active role in the regulation of membrane potential in vascular smooth muscle and vascular tone. These channels not only participate in the physiological responses to endogenously occurring substances, but also become the therapeutic targets for many synthetic drugs. Information regarding the role of K+ channels in vascular effects of female sex steroid hormones is scarce. We previously showed that K+ channel activation contributed in part to the estrogen-mediated vasorelaxation. In order to examine further whether steroid hormones may have direct interaction with K+ channels, we have recently expressed two types of K+ channels, KCa and KV channels in Xenopus oocytes. It was found that 17ß-estradiol increased the large-conductance KCa currents in a concentration-related manner. Tetraethylammonium ions or iberiotoxin inhibited the effect of 17ß-estradiol. KCa current was increased by NS 1619 and inhibited by progesterone. BSA-conjugated estrogen also increased KCa currents. Progesterone reduced the estrogen-stimulated KCa currents. KV1.5 channels were also expressed in Xenopus oocytes and inhibited by 4-aminopyridine. Progesterone reduced the KV1.5 current, while estrogen had little effect. These results showed that estrogen could stimulate KCa channels without an effect on KV1.5 channels. Progesterone inhibited the activity of both KCa and KV1.5 channels expressed in Xenopus oocytes. Progesterone was described to antagonize the vascular action of estrogen. Inhibition of K+ channels may be involved in the reported antagonistic effect of progesterone against the estrogen-induced vasorelaxation. (supported by UPGC Direct Grant)

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1540-8191.2002.101419.x

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9

Digitale Medien

Multiplicity in the Vascular Response to Pinacidil in Rat Mesenteric Artereies (2002)

Tsang, SY ; Yao, XQ ; Wong, CM ; [weitere]

350 Main Street , Malden , MA 02148 , USA. , and 9600 Garsington Road , Oxford OX4 2DQ , England . : Blackwell Science Inc

Journal of cardiac surgery 17 (2002), S. 0

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ISSN: 1540-8191

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Medizin

Notizen: Pinacidil is a clinically effective antihypertensive drug that directly relaxes vascular smooth muscle. Pinacidil activates both ATP-sensitive and Ca2+-activated K+ channels in vascular myocytes. However, it remains controversial whether activation of K+ channels and subsequent hyperpolarization mediates pinacidil-induced vasorelaxation, particularly when the concentration is higher than that reported for pinacidil-induced opening of KATP channels. In the present study, attempt was made to investigate the possible KATP channel-independent relaxant effect of pinacidil in isolated rat mesenteric arteries without endothelium. In phenylephrine-contracted rings, glibenclamide at 10 μM attenuated pinacidil-induced relaxation without an effect on the maximum relaxation. Pinacidil relaxed arteries contracted by U46619 and 60 mM K+ with respective IC50 of 0.19 and 16.7 μM. Some rings were first contracted by 60 mM K+ and then relaxed totally by 1 μM nifedipine in order to minimize the influence of both K+ channels and voltage-sensitive Ca2+ channels. Under this condition, U46619-induced tone was reduced by pinacidil (IC50 of 20.6 μM) and maximum relaxation can be achieved. Following inhibition of K+ and Ca2+ channels pinacidil-induced relaxation remained unchanged by pretreatment with 10 μM cyclopiazonic acid, the endoplasmic reticulum Ca2+-ATPase inhibitor or with 100 μM ouabain, the Na+-K+-ATPase inhibitor. Pretreatment with 30 μM Ni2+ caused parallel rightward shift of concentration-relaxation curve for pinacidil without affecting maximal relaxation. Besides, pinacidil also concentration-dependently relaxed rings preconstricted by active phorbol ester, phorbol 12,13-diacetate (1 μM). The present results indicate that the mechanisms by which pinacidil mediates vasorelaxation are multifactorial when its concentration is higher than 1 μM (supported by UPGC Direct Grant)

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1540-8191.2002.101418.x

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10

Digitale Medien

Altered Vascular Reactivity of the Cerebral Arteries in Ovariectomized Rat (2002)

Tsang, S.Y. ; Yao, X.Q. ; Chan, F.L. ; [weitere]

350 Main Street , Malden , MA 02148 , USA. , and 9600 Garsington Road , Oxford OX4 2DQ , England . : Blackwell Science Inc

Journal of cardiac surgery 17 (2002), S. 0

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ISSN: 1540-8191

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Medizin

Notizen: Estrogen has received considerable attention recently as a potential therapeutic agent in vascular pathophysiological states such as stroke. The mechanisms by which estrogen influences cerebral arteries are incompletely understood. The present study was to examine the effect of ovariectomy and chronic estrogen or tamoxifen treatment on vascular reactivity in rat posterior communicating cerebral arteries with intact endothelium. Changes in vascular tension were measured by microvessel myograph. Ovariectomy significantly enhanced the constricting responses to endothelin I, but not to phenylephrine. Chronic treatment with estrogen or tamoxifen partially reversed or abolished the effect of ovariectomy. The contraction induced by high K+ solution was also enhanced in the ovariectomized rats and this enhancement was abolished by estrogen or tamoxifen treatment. Ovariectomy potentiated the relaxant response to nicardipine but not NS 1619. Estrogen but not tamoxifen reversed the effect of ovariectomy. The present results indicate that chronic tamoxifen may not act as an antagonist of estrogen, instead, chronic treatment with estrogen and tamoxifen has similar effect in inhibiting the increased vascular tension induced by ovariectomy. This study suggests the influence of physiological level of estrogen on vascular contractility. It is at present unknown what may have caused increased relaxant effect of nicardipine, a L-type Ca2+ channel blocker. More experiments are needed to show the role of endothelium in the altered vascular contractility in the ovariectomized and estrogen-treated rats. (supported by UPGC Direct Grant).

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1540-8191.2002.101417.x

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