bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of the Oxytocin Receptor in Bovine Reproductive Tissues and the Role of Steroids
Authors: Ivell R , Fuchs A‐R , Bathgate R , Tillmann G , Kimura T
Published: July 2002

Contents

The oxytocin receptor (OTR) plays a central role in the functioning of the reproductive tract in the female ruminant. During the oestrous cycle endometrial OTR is suppressed through most of the cycle, probably in a progesterone‐dependent manner, to be massively up‐regulated during the few days before and after oestrus. At this time, luteal OT triggers a positive feedback loop, the endometrial OTR mediating the release of luteolytic PGF2α which feeds back to the corpus luteum to cause the secretion of more OT and to induce luteolysis. This feedback is only interrupted if a newly formed blastocyst is present. Ruminant blastocysts secrete the cytokine interferon‐τ, which interacts directly with the endometrial epithelial cells, preventing the up‐regulation of OTR in late luteal phase. During early pregnancy the levels of OTR in endometrium remain very low whereas myometrial OTR are less affected. OTR in endometrium are up‐regulated around day 50 and then progressively increase to reach a maximum at the onset of labour; those in the myometrium are upregulated somewhat later in gestation, around day 100. The OTR in the cervix are differently regulated: their concentrations are very low through most of the cycle and gestation and do not increase until pro‐oestrus and at parturition when they abruptly rise to high values. Ligand binding to the mucosal and endometrial OTR causes specific release of prostaglandins, which in turn activate paracrine pathways in the surrounding tissues to induce softening of the connective tissue of the uterine wall during pregnancy, and of the cervix at term. Additionally, local uterine contractions induced by OT and potentiated by prostaglandins may serve a physiological function during pregnancy by improving uterine blood flow. Due to the appearance of gap junctions in myometrium at term the OT‐induced contractions become synchronized and well propagated and because of concomitant cervical softening the contractions become expulsive. Although OTR‐dependent physiology correlates well with the levels of circulating gonadal steroids, there is no evidence for any direct effect of steroids either on the OTR gene or OTR protein. Instead, progesterone appears to exert an indirect inhibitory effect on the OTR gene, probably mediated via other cell types. This is in contrast to the inhibition by interferon‐τ which appears to activate a pathway which directly suppresses the OTR gene expression. The important role of OTR in female uterine physiology, and its value as an indicator molecule, make it imperative to understand the complex molecular mechanisms underlying its regulation. These are likely to be of fundamental importance for many aspects of uterine function both in ruminants and in other species, including the human.
Factors Associated with Home Versus Institutional Death Among Cancer Patients in Connecticut
Authors: Gallo William T. , Baker Matthew J. , Bradley Elizabeth H.
Published: July 2002

OBJECTIVE: To assess the relationships between home death and a set of demographic, disease‐related, and health‐resource factors among individuals who died of cancer.

DESIGN: Prospective cohort study.

SETTING: All adult deaths from cancer in Connecticut during 1994.

PARTICIPANTS: Six thousand eight hundred and thirteen individuals who met all of the following criteria: died of a cancer‐related cause in 1994, had previously been diagnosed with cancer in Connecticut, and were age 18 and older at the time of death.

MEASUREMENT: Site of death.

RESULTS: Twenty‐nine percent of the study sample died at home, 42% died in a hospital, 17% died in a nursing home, and 11% died in an inpatient hospice facility. Multivariate analysis indicated that demographic characteristics (being married, female, white, and residing in a higher income area), disease‐related factors (type of cancer, longer survival postdiagnosis), and health‐resource factors (greater availability of hospice providers, less availability of hospital beds) were associated with dying at home rather than in a hospital or inpatient hospice.

CONCLUSIONS: The implications of this study for clinical practice and health planning are considerable. The findings identify groups (men, unmarried individuals, and those living in lower income areas) at higher risk for institutionalized death—groups that may be targeted for possible interventions to promote home death when home death is preferred by patients and their families. Further, the findings suggest that site of death is influenced by available health‐system resources. Thus, if home death is to be supported, the relative availability of hospital beds and hospice providers may be an effective policy tool for promoting home death. J Am Geriatr Soc 49:771–777, 2001.
Medical Care Inconsistent with Patients' Treatment Goals: Association with 1‐Year Medicare Resource Use and Survival
Authors: Teno Joan M. , Fisher Elliott S. , Hamel Mary Beth , Coppola Kristen , Dawson Neal V.
Published: July 2002

OBJECTIVES:

To describe how frequently seriously ill persons perceive that the care they receive is inconsistent with treatment preferences and the effect on 1‐year resource utilization.

SETTING:

Five U.S. teaching hospitals.

DESIGN:

Secondary analysis of interview data.

PARTICIPANTS:

Seriously ill Medicare beneficiaries.

MEASUREMENTS:

Interviews about patients' preferred approaches to care and whether they perceived care was consistent with these preferences. Part A and B costs for up to 1 year, adjusted for cost differences across hospitals and over time and for 1‐year survival.

RESULTS:

Forty percent of the 1,185 study patients expressed a preference for treatment to focus on extending life, whereas 60% expressed a preference for comfort care. Eighty‐six percent of the patients who wanted aggressive treatment reported that care was consistent with their preferences, but only 41% of those who preferred comfort care reported that care was consistent with their preferences. More than one‐third of those with a preference for comfort care (35%) reported that the medical care that they received was inconsistent with their goals; 24% were unsure of treatment goals. Those who preferred comfort care but believed that their care was inconsistent with their wishes had higher estimated mean 1‐year costs than those who believed that their care was consistent with their wishes ($92,442 vs $52,098, P < .001). Even after adjusting for differences in disease severity, age, gender, race, functional status, income, and years of education, adjusted costs were 1.4 times (95% confidence interval = 1.2–1.6) higher. However, 1‐year survival was lower in these patients who stated that care was consistent with their preference to focus on comfort care than for those who wished to receive comfort care and stated that care was not consistent with their preference (38% vs 55% 1‐year survival, P < .001).

CONCLUSION:

More than one in three seriously ill persons who prefer comfort care believe that their medical care is at odds with their preference that treatment focus on palliation. Such discord was associated with higher 1‐year healthcare costs and increased survival. J Am Geriatr Soc 50:496–500, 2002.
Does Receipt of Hospice Care in Nursing Homes Improve the Management of Pain at the End of Life?
Authors: Miller Susan C. , Mor Vincent , Wu Ning , Gozalo Pedro , Lapane Kate
Published: July 2002

OBJECTIVES:

To compare analgesic management of daily pain for dying nursing home residents enrolled and not enrolled in Medicare hospice.

DESIGN:

Retrospective, comparative cohort study.

SETTING:

Over 800 nursing homes in Kansas, Maine, Mississippi, New York, and South Dakota.

PARTICIPANTS:

A subset of residents with daily pain near the end of life taken from a matched cohort of hospice (2,644) and nonhospice (7,929) nursing home residents who had at least two resident assessments (Minimum Data Sets (MDSs)) completed, their last between 1992 and 1996, and who died before April 1997. The daily pain subset consisted of 709 hospice and 1,326 nonhospice residents.

MEASUREMENTS:

Detailed drug use data contained on the last MDS before death were used to examine analgesic management of daily pain. Guidelines from the American Medical Directors Association (AMDA) were used to identify analgesics not recommended for use in managing chronic pain in long‐term care settings. The study outcome, regular treatment of daily pain, examined whether patients received any analgesic, other than those not recommended by AMDA, at least twice a day for each day of documented daily pain (i.e., 7 days before date of last MDS).

RESULTS:

Fifteen percent of hospice residents and 23% of nonhospice residents in daily pain received no analgesics (odds ratio (OR) = 0.57, 95% confidence interval (CI) = 0.45–0.74). A lower proportion of hospice residents (21%) than of nonhospice residents (29%) received analgesics not recommended by AMDA (OR = 0.65, 95% CI = 0.52–0.80). Overall, acetaminophen (not in combination with other drugs) was used most frequently for nonhospice residents (25% of 1,673 prescriptions), whereas morphine derivatives were used most frequently for hospice residents (30% of 1,058 prescriptions). Fifty‐one percent of hospice residents and 33% of nonhospice residents received regular treatment for daily pain. Controlling for clinical confounders, hospice residents were twice as likely as nonhospice residents to receive regular treatment for daily pain (adjusted odds ratio = 2.08, 95% CI = 1.68–2.56).

CONCLUSION:

Findings suggest that analgesic management of daily pain is better for nursing home residents enrolled in hospice than for those not enrolled in hospice. The prescribing practices portrayed by this study reveal that many dying nursing home residents in daily pain are receiving no analgesic treatment or are receiving analgesic treatment inconsistent with AMDA and other pain management guidelines. Improving the analgesic management of pain in nursing homes is essential if high‐quality end‐of‐life care in nursing homes is to be achieved. J Am Geriatr Soc 50:507–515, 2002.
Temporal and spectral characteristics of soft x radiation from laser-irradiated cylindrical cavities
Authors: Weber R. , Cunningham P. F. , Balmer J. E.
Published: July 2002

Cylindrical cavity targets with inner diameters between 200 and 300 μm have been irradiated with 4 J, 80 ps, Nd:glass laser pulses through a 100-μm-wide longitudinal slit. From the spatially resolved temporal and spectral behavior of the x-ray emission along the axis, data on temperature and density of the expanding primary and secondary plasmas and of the region of collision have been obtained.
High Q coplanar transmission line resonator of YBa2Cu3O7−x on MgO
Authors: Valenzuela A. A. , Russer P.
Published: July 2002

We present the first coplanar waveguide transmission line resonator patterned from a perovskite high Tc superconducting film at 9 GHz. At 77 K the unloaded quality factor Q0 of the resonator patterned from a YBa2Cu3O7−x film on a MgO substrate is 1300, that is, 14 times higher than that of the copper resonator and 17 times higher than that of the gold resonator at the same temperature. At 4.2 K a Q0 factor of 3300 was measured for the YBa2Cu3O7−x /MgO resonator. Simple calculations of the quality factor show that values of 10 000 at 77 K should be possible using better substrates, films, and etching techniques. This resonator could form the basic structure of more complex microwave filter systems operating at liquid-nitrogen temperatures.
Thermal stability of electro-optic response in poled polyimide systems
Authors: Wu J. W. , Valley J. F. , Ermer S. , Binkley E. S. , Kenney J. T. , Lipscomb G. F. , Lytel R.
Published: July 2002

Using polyimide as host in a guest-host thin film we demonstrate the first poled-polymer electro-optic response stable at temperatures up to 150 °C (samples poled and cured at 250 °C). A coplanar-electrode poling geometry is used so that the molecular alignment of the guest dye between the electrodes is coincident with the free volume of the host. We hypothesize that ‘‘high’’ temperature poling during the imidization process, when the polyimide forms rings and densifies, accounts for the excellent poled response stability.
Perpendicular magnetization in Ni/Pt multilayers
Authors: Krishnan R. , Lassri H. , Porte M. , Tessier M. , Renaudin P.
Published: July 2002

Ni/Pt multilayers have been prepared by electron beam evaporation under ultrahigh vacuum conditions. All the samples were grown at 300 K. The t(Ni) was in the range 0.7–2.1 nm and t(Pt) was fixed at 2 nm. The magnetization and the Curie temperature for these samples are lower than that of bulk Ni. For the samples with t(Ni)≤1 nm perfect rectangular hysteresis loops are obtained along the film normal in the low temperature range (5 to 70 K) indicating the presence of a strong uniaxial anisotropy. The coercivity for the sample with t(Ni)=0.7 nm at 5 K is as high as 4.7 kOe.
Energy level of the nitrogen dangling bond in amorphous silicon nitride
Authors: Warren W. L. , Kanicki J. , Robertson J. , Lenahan P. M.
Published: July 2002

The composition dependence and room-temperature metastability of the paramagnetic nitrogen dangling-bond center is amorphous silicon nitride suggest that its energy level lies close to the N pπ states, in agreement with theoretical calculations.
Resonant Stark tuning of second-order susceptibility in coupled quantum wells
Authors: Sirtori Carlo , Capasso Federico , Sivco Deborah L. , Hutchinson A. L. , Cho Alfred Y.
Published: July 2002

The first observation of the resonant Stark tuning of second harmonic generation is reported. Our AlInAs/GaInAs asymmetric coupled-well structures are engineered in such a way that certain intersubband transitions (1→2 and 2→3) exhibit a large Stark shift equal to the potential drop between the centers of the wells. Thus the second-order susceptibility ‖χ(2)2ω‖ exhibits a pronounced peak when the bound states are made equally spaced by the application of an electric field and ℏω=ΔE12. A peak ‖χ(2)2ω‖=7.5×10−8 m/V, approximately 200 times the bulk values in InAs and GaAs, has been measured.
Efficient coupling of high-intensity subpicosecond laser pulses into solids
Authors: Murnane M. M. , Kapteyn H. C. , Gordon S. P. , Bokor J. , Glytsis E. N. , Falcone R. W.
Published: July 2002

We demonstrate a new technique for enhancing the absorption of high-intensity, ultrashort-duration laser pulses by solids. Targets consisting of gold gratings and gold clusters were found to absorb greater than 90% of the incident high-intensity laser light. This is in contrast to less than 10% absorption by flat surfaces. As a result of this strong coupling of the laser to a high-density plasma, conversion efficiency of laser energy to x rays of greater than 1% was observed for x rays above 1 keV. Efficiency of nearly 25% was observed for emissions greater than 30 eV. These conversion efficiencies are more than an order of magnitude greater than those measured from flat targets.
Second-harmonic generation in asymmetric Si/SiGe quantum wells
Authors: Seto M. , Helm M. , Moussa Z. , Boucaud P. , Julien F. H. , Lourtioz J.-M. , Nützel J. F. , Abstreiter G.
Published: July 2002

The observation of infrared second-harmonic generation in asymmetric Si/SiGe p-doped quantum wells is reported. The generated signal stems entirely from valence intersubband transitions, since bulk Si, with an inversion symmetric crystal structure, has a zero second-order susceptibility. The experiments were performed using a Q-switched CO2 laser operating at 10.56 μm and give a nonlinear susceptibility of 5×10−8 m/V.
Hydrogen induced vibrational and electronic transitions in chemical vapor deposited diamond, identified by isotopic substitution
Authors: Fuchs F. , Wild C. , Schwarz K. , Müller-Sebert W. , Koidl P.
Published: July 2002

Homoepitaxial diamond films grown by chemical vapor deposition from 12C and 13C containing gases have been studied by Fourier transform infrared spectroscopy. A sharp absorption band observed at 3123 cm−1 is attributed to a CH vibrational absorption. It resembles the previously observed 3107 cm−1 absorption band in natural diamond. Isotopic replacement of carbon, hydrogen, and nitrogen by 13C, 2H, and 15N reveals, that a CH center without nitrogen participation is responsible for this new absorption. Furthermore, new hydrogen related electronic transitions have been observed around 7300 cm−1. These lines shift to higher energies in 13C crystals, in accordance with the increase of the electronic band gap.
Amorphous Si/SiC three-color detector with adjustable threshold
Authors: de Cesare G. , Irrera F. , Lemmi F. , Palma F.
Published: July 2002

An adjustable threshold color detector (ATCD) is demonstrated, based on a hydrogenated amorphous silicon (a-Si:H) and silicon–carbide (a-SiC:H) p+-i-n+-i-n+-i-p+ multilayer. The ATCD is able to discriminate between blue (λ=450 nm), green (550 nm), and red (≳650 nm) illumination by varying the externally applied voltage within a few volts. The operation of the detector can be explained regarding the ATCD as three independent devices connected in series: a p+-i-n+, a n+-i-n+, and a n+-i-p+. The novel feature is the n+-i-n+ cell. It acts as a short circuit under strong illumination, whereas in dark it is equivalent to two low quality back-to-back diodes which introduce a shift in the threshold in the photocurrent detection. Thanks to the large number of physical parameters such as layer thickness and band gap the ATCD appears extremely versatile.
High-resolution x-ray spectrometer for an electron beam ion trap
Authors: Beiersdorfer P. , Marrs R. E. , Henderson J. R. , Knapp D. A. , Levine M. A. , Platt D. B. , Schneider M. B. , Vogel D. A. , Wong K. L.
Published: July 2002

A high-throughput von Hámos-type Bragg crystal spectrometer is described that is operated with the Livermore electron beam ion trap. The spectrometer is employed to measure high-resolution x-ray spectra from highly charged heliumlike and neonlike ions. Data from heliumlike Ti20+ and Fe24+ and from neonlike Au69+ are presented to demonstrate the utility of the new instrument.
Gauge for nondestructive measurement of the internal pressure in powder-filled evacuated panel superinsulation
Authors: Kollie Thomas G. , Thacker L. H.
Published: July 2002

A gauge that measures the internal pressure (P) in powder-filled evacuated panels (PEPs) is described. PEPs are superinsulators consisting of high thermal resistivity powders encapsulated in hermetically sealed flexible barriers enclosing a vacuum. To measure P, the gauge supplies a vacuum to the outer surface of the barrier. When the P in the PEP exceeds that supplied by the gauge, the barrier deflects. This deflection is sensed by a bifurcated-fiber-optic light system that converts the motion of the barrier into a voltage proportional to the displacement of the barrier. A pressure transducer mounted in the gauge provides a dc voltage proportional to P at the interface of the barrier and PEP. An X-Y recorder displays the relationship between these two signals. Experiments show that the gauge yields P measurements with uncertainties of +0.27 kPa and reproducibilities of ±0.16 kPa for PEPs with 0.13-mm-thick flexible polymer barriers. To achieve more accurate measurements, the gauge should first be calibrated on a PEP of known internal P then used to measure P on similar PEPs with unknown P’s. Besides PEPs, experiments suggest that the gauge can nondestructively and rapidly measure the pressure in a hermetically sealed container having a flexible enclosure, such as vacuum-packaged food. Patent applications for this gauge are on file with the United States Patent Office.
A linear ultraviolet flashlamp with self-replenishing cathode
Authors: Wekhof Alex
Published: July 2002

The design of this linear ultraviolet (UV) flashlamp ensures an equilibrium between the mercury cathode erosion and the return of mercury atoms from the discharge, making the cathode self-replenishing. The lamp, which requires a simmer current of only 0.3 A, can operate in the region of high pulse peak currents and current densities where a conventional xenon flashlamp experiences a rapid deterioration. The lamp has a minimal length of 7.5 cm and can be loaded up to 100 W/cm. It has demonstrated about 30% output in the UV region and has proven efficient for dissociation of organic compounds and for disinfection, and has promise for other photochemical applications.
Generating a jet of deagglomerated small particles in vacuum
Authors: Poppe T. , Blum J. , Henning Th.
Published: July 2002

We describe a dust jet generator, which is a device for the deagglomeration of micron-sized and submicron-sized dust particles. In contrast to other mechanisms, it principally works without any gas and generates a dust jet with a speed up to 100 m/s relative to the surrounding gas. Compressed dust powder is fed onto the front side of a fast rotating cogwheel. Upon contact with the cogwheel, the dust is deagglomerated and the single particles are accelerated at a tangent to the circumference. Design details of the mechanism and characteristics of the dust jet are presented. We will use the dust jet for the investigation of collisions of individual particles with surfaces or other particles. Other possible applications of the dust jet generator are proposed.
A new surface science in situ transmission and reflection electron microscope
Authors: Marshall M. T. , McDonald M. L. , Tong X. , Yeadon M. , Gibson J. M.
Published: July 2002

We describe an ultrahigh vacuum instrument for transmission electron microscopy and reflection electron microscopy for the study of surfaces and thin film growth. The focus of previous experiments was on the high spatial resolution (<3 Å) generally associated with microscopy, at the cost of controlled growth and characterization. We have taken a different approach. It has been shown that most experiments using diffraction and diffraction contrast imaging can be performed well at poorer resolution (∼20 Å), including the imaging of monatomic steps and monolayer coverages. The instrument is designed for best control of growth and vacuum, with sacrifices in optical resolution, which is theoretically ∼2 nm. The instrument is called SHEBA (surface high-energy electron beam apparatus). We can examine a ∼1 cm2 sample in both transmission electron microscopy and reflection electron microscopy, in situ with well-controlled molecular beam epitaxy (MBE) growth capabilities, well characterized vacuum, and surface characterization by Auger spectroscopy and low-energy electron diffraction. Preliminary experiments of cobalt on silicon have shown MBE growth rates ranging from 1.5 monolayers per hour to 18.3 monolayers per hour depending on the temperature of the evaporation source. Using SHEBA for a reactive MBE experiment has provided the first direct evidence of the formation of aluminum nitride by nitridation of basal plane sapphire. The most serious design problems were stray magnetic fields and mechanical vibrations. These have been overcome and allow a spatial resolution of <10 nm. The instrument is expected to be very valuable in studies of film growth.
Imaging conoscope for investigation of optical inhomogeneity in large boules of uniaxial crystals
Authors: Bajor Andrzej L. , Sałbut Leszek , Szwedowski Andrzej , Pia̧tkowski Tadeusz
Published: July 2002

The name “conoscope” in Greek suggests that this tool should be used for observing interference patterns of birefringent crystals in the convergent beam of light. As such, the conoscope has been frequently used in laboratories for quick and usually qualitative estimation of optical inhomogeneity of crystals. In this paper we have described details of the computer-controlled imaging conoscope used for quantitative investigation of optical inhomogeneity in uniaxial crystals. To the best of our knowledge, this is the first conoscope used in an automated arrangement. Its working is based on equations derived for a plane–parallel uniaxial crystal plate cut out obliquely to the optical axis, which is next applied for two specific plate orientations practically investigated, i.e. for plates cut out perpendicularly and parallelly to this axis. It was found that these equations are more accurate than those published by other investigators. A practical investigation of a LiNbO3 crystal pulled by the Czochralski method from a congruent melt has been presented. Two birefringence inhomogeneity maps acquired for the above-mentioned two specific orientations in this crystal were used for eliminating its inhomogeneous areas from further use in optics. A theoretical error analysis carried out also in this work has shown that the optical inhomogeneity could be detected with a relative error usually not exceeding a small fraction of a percent.
Diffusion of Sb in relaxed Si1−xGex
Authors: Larsen Arne Nylandsted , Kringho/j Per
Published: July 2002

Diffusion of antimony in relaxed Si1−xGex alloy layers grown by molecular beam epitaxy has been studied as a function of the composition for 0≤x≤0.5. The diffusivity of antimony was found to increase with the Ge alloy content, and the extracted activation energies for diffusion were found to decrease with increasing germanium content in the investigated composition range. The activation energies, however, are significantly higher than the corresponding activation energies obtained by an extrapolation between the activation energy in pure silicon and germanium.
Coulomb blockade oscillations at room temperature in a Si quantum wire metal-oxide-semiconductor field-effect transistor fabricated by anisotropic etching on a silicon-on-insulator substrate
Authors: Ishikuro H. , Fujii T. , Saraya T. , Hashiguchi G. , Hiramoto T. , Ikoma T.
Published: July 2002

We have developed a very controllable fabrication process of an extremely narrow (∼10 nm) quantum wire metal-oxide-semiconductor field-effect transistor (MOSFET) on a separation-by-implanted-oxygen (SIMOX) substrate using anisotropic etching and selective oxidation technique. The drain current versus gate voltage characteristics show oscillations caused by Coulomb blockade even at room temperature. The oscillations split into several sharp peaks when the temperature is decreased, indicating that the channel is separated by several serial coupled quantum dots and that the quantum levels of these dots correspond to the observed fine peaks.
Local amorphous thin-film crystallization induced by focused electron-beam irradiation
Authors: Libera M.
Published: July 2002

Crystallization is induced in amorphous 80 nm films of Ge48Te52 by electron irradiation to produce structures with characteristic dimensions as small as of 10–100 nm. The experiments are performed in a 200 keV field-emission scanning transmission electron microscope (TEM/STEM) that provides an electron probe about 1–2 nm in diameter (FWHM) with approximately 1 nA of current. When entire films are annealed in the absence of electron irradiation, they crystallize at approximately 450 K. Crystallization occurs under focused-probe electron irradiation when the average film temperature is as low as 300 K. The local transformation is driven by some combination of electron-beam heating and radiation-defect generation. A discussion is presented in the context of related nanocrystallization experiments driven by scanned-probe techniques for optical data storage applications.
Nearest-neighbor distance distribution of diamond nuclei on substrate surfaces
Authors: Ascarelli P. , Cappelli E. , Pinzari F.
Published: July 2002

The origin of a nucleation density depletion around each diamond nucleus on a Si substrate surface is here related to a deformation zone induced by the diamond-substrate lattice misfit. This phenomenon determines a limitation on the maximum nucleation density obtainable.
Electro-optic measurement of THz field pulses with a chirped optical beam
Authors: Jiang Zhiping , Zhang X.-C.
Published: July 2002

Using a linearly chirped optical probe pulse in free-space electro-optic measurements, a temporal wave form of a co-propagating THz field is linearly encoded onto the frequency spectrum of the optical probe pulse, and then decoded by dispersing the probe beam from a grating to a detector array. We achieve acquisition of picosecond THz field pulses without using mechanical time-delay device. We also demonstrate a single-shot electro-optic measurement of the temporal wave form of a THz pulse.
Size-dependent superparamagnetic properties of MgFe2O4 spinel ferrite nanocrystallites
Authors: Chen Qi , Zhang Z. John
Published: July 2002

Superparamagnetism is a unique and important aspect of magnetism in nanoparticles. The superparamagnetic properties of the MgFe2O4 spinel ferrite nanoparticles with the particle size from about 6 to 18 nm are studied. The blocking temperature is a function of the particle size and increases with increasing particle size. The coercivity of MgFe2O4 nanoparticles also is a function of the particle size below the blocking temperature. When the temperature rises above the blocking temperature, the nanoparticles show nonhysteresis magnetization behaviors. With these interesting superparamagnetic properties, MgFe2O4 nanoparticles have potentials for applications such as ferrofluids, magnetocaloric refrigeration, and the contrast agents for magnetic resonance imaging.
InAsSb/InAsP strained-layer superlattice injection lasers operating at 4.0 μm grown by metal-organic chemical vapor deposition
Authors: Lane B. , Wu Z. , Stein A. , Diaz J. , Razeghi M.
Published: July 2002

We report high power mid-infrared electrical injection operation of laser diodes based on InAsSb/InAsP strained-layer superlattices grown on InAs substrate by metal-organic chemical vapor deposition. The broad-area laser diodes with 100 μm aperture and 1800 μm cavity length demonstrate peak output powers of 546 and 94 mW in pulsed and cw operation respectively at 100 K with a threshold current density as low as 100 A/cm2.
Selective nucleation and growth of carbon nanotubes at the CoSi2/Si interface
Authors: Biró L. P. , Molnár G. , Szabó I. , Vértesy Z. , Horváth Z. E. , Gyulai J. , Kónya Z. , Piedigrosso P. , Fonseca A. , Nagy J. B. , Thiry P. A.
Published: July 2002

A patterned CoSi2/Si substrate was used for the catalytic growth of carbon nanostructures and nanotubes in the temperature range of 750–800 °C, using acetylene/N2 as a reaction mixture flowing through a quartz tube at ambient pressure. Selective nucleation confined to the CoSi2/Si interface region was achieved. Scanning electron microscopy and transmission electron microscopy were used to investigate the grown nanostructures.
Influence of dislocations on the magnetic structure of two-dimensional anisotropic antiferromagnets
Authors: Dudko O. K. , Kovalev A. S.
Published: July 2002

For an easy-plane antiferromagnet having anisotropy in the easy plane and containing an edge dislocation, a two-dimensional model is formulated which generalizes the Peierls model to the case of coupled fields of magnetization and elastic displacements. The proposed model is used to obtain a system of one-dimensional nonlinear integrodifferential equations for the two coupled fields. In the case of ideal crystal structure of the antiferromagnet this system of equations has a solution for a domain wall containing a Bloch line, the structure into which the magnetic vortex is transformed when the single-ion anisotropy is taken into account. In the presence of a dislocation a complex magnetostructural topological defect arises in the form of a 180° domain wall terminating on the dislocation.
The Li2 F 1Σg+ “shelf” state: Accurate potential energy curve based on the inverted perturbation approach
Authors: Pashov A. , Jastrzȩbski W. , Kowalczyk P.
Published: July 2002

We report an accurate inverted perturbation approach (IPA) potential energy curve for the “shelf” F 1Σg+ state in Li2 which reproduces positions of the experimental energy levels available in the literature for all three isotopomers Li27, Li76Li, and Li26 with a standard deviation of 0.11 cm−1. Our analysis significantly improves the shape of the recently reported Rydberg–Klein–Rees (RKR) potential curve of the F 1Σg+ state [Antonova et al., J. Chem. Phys. 112, 7080 (2000)] and provides evidence for the existence of a shallow minimum in the shelf region. Using our IPA potential curve we were able to localize and identify some local perturbations in the spectra, as well as to correct the assignment of several spectral lines previously observed experimentally.
Measurement of the hyperfine structure in low-l, high-n Rydberg states of ortho H2 by millimeter wave spectroscopy
Authors: Osterwalder A. , Seiler R. , Merkt F.
Published: July 2002

Millimeter wave spectroscopy has been used to record high-resolution spectra of high-n (n=51–64), low-l (l=1–3) Rydberg states of ortho H2 located below the N+=1 rotational level of the X 2Σg+(v+=0) ground vibronic state of H2+. The spectral resolution of better than 1 MHz enables the observation of the hyperfine structure in these spectra. A simple procedure, based on the determination of combination differences, is used to reconstruct the energy level structure in np, nd, and nf Rydberg states of H2. The Stark effect is used to distinguish experimentally between p and f Rydberg states. In the weakly penetrating nf series, the hyperfine interaction dominates and the observed hyperfine components are of mixed singlet (S=0) and triplet (S=1) character. In the penetrating np series, the dominant interactions are between the electron orbital and spin angular momenta and the molecular rotation and the observed hyperfine components are characterized by a well-defined total electron spin. The nd Rydberg states show a behavior intermediate between these two limiting cases. The observed levels are of mixed singlet (S=0) and triplet (S=1) character but the main energy separation departs from the energy separation between the Gc=1/2 and Gc=3/2 levels of the H2+ ion.
An efficient finite field approach for calculating static electric polarizabilities of periodic systems
Authors: Kudin Konstantin N. , Scuseria Gustavo E.
Published: July 2002

We introduce an efficient finite-field approach for calculating static polarizabilities of periodic systems. Our method yields polarizabilities that exactly match the oligomer extrapolation values. Theoretical details are given and benchmark calculations presented.
Nucleation and growth of carbon nanotubes by microwave plasma chemical vapor deposition
Authors: Bower Chris , Zhou Otto , Zhu Wei , Werder D. J. , Jin Sungho
Published: July 2002

The nucleation and growth of aligned multiwall carbon nanotubes by microwave plasma-enhanced chemical vapor deposition have been studied. The nanotubes nucleate and grow from catalytic cobalt islands on a silicon substrate surface, with both their diameter and length dependent on the size of the cobalt islands. Electron microscopy reveals that the nanotubes grow via a “base growth” mechanism. The nanotubes grow initially at a very rapid and constant rate (∼100 nm/s) that decreases sharply after the catalyst Co particles become fully encapsulated by the nanotubes. We propose a detailed model to explain these experimental observations on nucleation and growth of nanotubes.
Magnetic tweezers for DNA micromanipulation
Authors: Haber Charbel , Wirtz Denis
Published: July 2002

We detail the design of an electromagnetic assembly capable of generating a constant magnetic field superimposed to a large magnetic field gradient (between 40 and 100 T/m), which was uniform over a large gap (between 1.5 and 2 cm). Large gaps allowed the use of wide high numerical-aperture lenses to track microspheres attached to DNA molecules with an inverted light microscope. Given the geometric constraints of the microscope, computer-aided design was used to optimize the magnetic field gradient linearity, homogeneity, and amplitude, as well as the arrangement of the magnetic coils, the currents, and the mechanical stability of the assembly. The assembly was used to apply forces of controlled amplitude, direction, and time dependence on superparamagnetic microspheres by using magnetic coils instead of permanent magnets. A streptavidin-coated microsphere was attached to the 3′ end of a λ-phage DNA molecule through a single biotin molecule. The 5′ end of the λ-phage DNA molecule was tethered to a glass coverslip by conjugating the DNA’s overhang to a complementary 12 base-pair primer, which was itself cross-linked to a heterobifunctional group placed on the glass coverslip. By tracking the centroid of this microsphere, the mechanical response of a single λ-phage DNA molecule was measured as a function of the applied magnetic force. The resulting force-extension curve was fitted with the worm-like-chain model to obtain λ-phage DNA’s persistence length and contour length, which were in agreement with previous reports.
Critical phenomena of water bridges in nanoasperity contacts
Authors: He Mingyan , Szuchmacher Blum Amy , Aston D. Eric , Buenviaje Cynthia , Overney René M. , Luginbühl Reto
Published: July 2002

This article discusses capillary forces measured by scanning force microscopy (SFM), which, as recently reported, show a discontinuous behavior at a low relative humidity between 20% and 40% depending on the solid surfaces. A capillary force discontinuity is very interesting in terms of a possible phase change or restructuring transition of bulk water in the interfacial solid–liquid region. Unfortunately, we have found that SFM measurements show an inherent weakness in the determination of the origin of the forces that are obtained during pull-off measurements. This article critically discusses the origin of the adhesive interactions as a function of relative humidity with chemically modified probing surfaces. Our measurements indicate that force discontinuities in pull-off measurements are strongly affected by the inability of the liquid to form capillary necks below a critical threshold in relative humidity. In the course of this article, we will discuss roughness effects on capillary forces and provide a modified capillary force equation for asperity nanocontacts.
A symmetry-adapted Lanczos method for calculating energy levels with different symmetries from a single set of iterations
Authors: Wang Xiao-Gang , Carrington Tucker
Published: July 2002

We present a symmetry-adapted Lanczos method that uses projection operators to calculate energy levels with different symmetries from a single sequence of matrix–vector products. Compared with the conventional Lanczos method, this method has the advantage that energy levels are computed more efficiently and with symmetry labels. High-lying stretching energy levels of a coupled Morse oscillator Hamiltonian describing SiH428 are calculated to demonstrate the advantage of the symmetry-adapted method.
Magnetoresistance properties of quasi-two-dimensional charge-density wave compounds AMo6O17 (A=Na, K, and Tl)
Authors: Tian Ming-Liang , Yue Song , Li Shiyan , Zhang Yuheng , Shi Jing
Published: July 2002

Temperature dependence of resistivity in quasi-two-dimensional purple bronzes AMo6O17 (A=Na, K, and Tl) has been comparatively studied between 2 and 300 K at different magnetic fields. Huge positive magnetoresistance (MR) behavior below the Peierls transition temperature TP∼110 K was found in both K/Tl purple bronzes for H∥c, but only a weak one in the Na purple bronze. At lower temperature TM∼16 K, a second anomaly of the resistivity, which moved to higher temperatures under a magnetic field, was also observed in both K/Tl compounds, with no corresponding anomaly in the Na purple bronze. For H⊥c, the MR effect becomes much weaker in all three compounds. These results suggest that the second anomaly is possibly related to the second Peierls instability, and the huge MR effect results from the large modification of the third FS along the [100] direction induced by the magnetic field, in which the third FS is imperfectly nested in K/Tl purple bronzes and absent in the Na purple bronze.
Turbulent Rayleigh–Bénard convection in gaseous and liquid He
Authors: Chavanne X. , Chillà F. , Chabaud B. , Castaing B. , Hébral B.
Published: July 2002

In this article we deal with the turbulent regimes of Rayleigh–Bénard convection, namely the 2/7 regime and beyond. An experiment with He at low temperature allows us to explore a large Rayleigh number (Ra) range up to 2×1014, under Boussinesq conditions, while the Prandtl number (Pr) is equal to and larger than 0.7. Calorimetric measurements evidence a departure from the 2/7 regime above Ra=1011 toward a new regime where the heat transfer is enhanced. Local measurements with two nearby thermometers allows us to relate this change to a laminar–turbulent transition of the velocity boundary layer induced by the large-scale flow near the walls of the cell. The features of the observed new regime match those of the ultimate regime predicted by R. Kraichnan [Phys. Fluids 5, 1374 (1962)] at moderate Pr; in particular, our experimental data show that the thermal boundary layer lies inside the viscous sublayer of the turbulent boundary layer.
Adsorption of branched homopolymers on a solid surface
Authors: Striolo Alberto , Prausnitz John M.
Published: July 2002

Simulation calculations are reported for single-chain polymer–wall conformation-averaged potentials of mean force and segment-density profiles for homopolymers of different structures as a function of the segment–wall attractive potential. When there is no attraction between the wall and the polymer segments, the presence of the wall generates a polymer-segment depletion layer whose thickness depends on polymer structure and on surface roughness. Segment-density profiles are characterized by three regions. In the proximal region, the segment density is determined by surface roughness and by polymer flexibility. In the distal region, the segment density approaches unity asymptotically. In the central region, the segment density depends on geometric characteristics of the polymer in the bulk solution. When the wall–segment attractive potential is sufficiently large, the depletion layer thickness is reduced and the polymers are adsorbed. When attraction is weak, compact polymers (e.g., dendrimers of high generation) are readily adsorbed. Due to their globular shape, high-generation dendrimers, at weak attractive interactions, are at contact with the surface with numerous segments; globular polymers experience a relatively small entropic penalty for adsorption. By contrast, linear polymers, due to their flexibility at good solvent conditions, pay a high entropic penalty for each segment at contact with the surface. Therefore, at weak attractive interactions, globular polymers are readily adsorbed, whereas linear polymers are more readily adsorbed at stronger attractive interactions. With rising surface roughness, flexible polymers tend to spread on the surface, whereas branched polymers are repelled at larger distances.
Extrinsic and intrinsic magnetoresistance contributions of CrO2 thin films
Authors: Rüdiger U. , Rabe M. , Samm K. , Özyilmaz B. , Pommer J. , Fraune M. , Güntherodt G. , Senz St. , Hesse D.
Published: July 2002

The growth of (010)-oriented CrO2 thin films on Al2O3(0001) substrates leads to a higher grain boundary density than the growth of (100)-oriented CrO2 thin films on isostructural TiO2(100) substrates. For both types of films an intrinsic linear contribution to the high field magnetoresistance (MR) due to spin disorder has been determined at T=300 K. This contribution does not depend on the crystalline quality of the films and supports the suggested intrinsic double exchange mechanism for CrO2. At low temperature (T=10 K) intergrain tunneling MR and Lorentz MR appear, which strongly depend on the crystalline properties of the CrO2 films.
Analytical investigations of an electron–water molecule pseudopotential. I. Exact calculations on a model system
Authors: Turi László , Gaigeot Marie-Pierre , Levy Nicolas , Borgis Daniel
Published: July 2002

Exact quantum mechanical calculations on the excess electronic states of the electron–water molecule system have been performed in the static-exchange approximation. The computational model includes a steep, but smooth confining potential which keeps the excess electron in the vicinity of the neutral molecule. Elimination of the core states of the water molecule by the application of the Phillips–Kleinman repulsion operator, and the removal of the large core oscillations of the wave function of the excess electron by the linear combination of the core states and the valence state result in a smooth pseudo-wave function. The pseudo-wave function has proper asymptotic behavior with the correct eigenvalue, and, thus, can serve as a model for comparisons to test the validity of various approximations employed in electron–molecule pseudopotential theory. From the comparisons we conclude that of the most commonly used approximations for the repulsion and the exchange operators only the combination of the local repulsion (LR) approximation and the semiclassical exchange (SCE) works partly satisfactorily. This particular combination reproduces the exact eigenvalue reasonably well, whereas the fit of the electron density is moderate. Although the calculated local potential, based on the LR-SCE approximation, is similar in its most characteristic features to those employed earlier for hydrated electron calculations, we propose this potential to be considered as a reasonable starting point for further work. Since the other examined approximations fail seriously, we find them inappropriate to use in the development of a new effective pair potential.
Optical limiting behavior of octa-decyloxy metallo-phthalocyanines
Authors: Sanghadasa Mohan , Shin In-Seok , Clark Ronald D. , Guo Huaisong , Penn Benjamin G.
Published: July 2002

One of the key issues involved in the development of passive optical power limiters is the search for appropriate materials that show effective reverse saturable absorption. Metallo-phthalocyanines seem to be good candidates for such applications because of their high optical nonlinearity and their unique electronic absorption characteristics. A series of 1,4,8,11,15,18,22,25-octa-decyloxy metallo-phthalocyanines containing palladium, nickel, cobalt, copper, and zinc as central metal atoms were characterized for their nonlinear absorptive properties to evaluate their suitability to function as reverse saturable absorbers. Nonlinear transmission measurements were analyzed in terms of a five-state model and a simple model based on the effective excited-state absorption cross sections without ascribing their origin to the states involved. Optical limiting thresholds were also estimated and compared with the absorption cross sections.
Magnetically soft, high-moment, high-resistivity thin films using discontinuous metal/native oxide multilayers
Authors: Beach G. S. D. , Berkowitz A. E. , Parker F. T. , Smith David J.
Published: July 2002

Multilayers consisting of discontinuous metal layers with native oxide surfaces have been fabricated using CoxFe100−x alloys ranging in composition from pure Co to pure Fe. For the Fe-containing compositions, the composites are magnetically soft with resistivities in the range of 100 to 2000 μΩ cm. Mössbauer spectroscopy indicates a magnetically ordered Fe-oxide component, and the magnetic moment of the oxide phase for pure Fe/native oxide multilayers has been determined.
CO adsorption on hydrogen saturated Ru(0001)
Authors: Riedmüller B. , Ciobı̂că I. M. , Papageorgopoulos D. C. , Frechard F. , Berenbak B. , Kleyn A. W. , van Santen R. A.
Published: July 2002

The interaction of CO with the Ru(0001)(1×1)H surface has been studied by density functional theory (DFT) periodic calculations and molecular beam techniques. The hydrogen (1×1) phase induces an activation barrier for CO adsorption with a minimum barrier height of 25 kJ mol−1. The barrier originates from the initial repulsive interaction between the CO-4σ and the Ru-d3z2-r2 orbitals. Coadsorbed H also reduces the CO adsorption energy considerably and enhances the site preference of CO. On a Ru(0001)(1×1)H surface, CO adsorbs exclusively on the atop position.