bluuebunny/crossref_metadata_2025 huggingface dataset:
Congenital Short QT Syndrome and Implantable Cardioverter Defibrillator Treatment:
Authors: SCHIMPF RAINER , WOLPERT CHRISTIAN , BIANCHI FRANCESCA , GIUSTETTO CARLA , GAITA FIORENZO , BAUERSFELD URS , BORGGREFE MARTIN
Published: December 2003

Introduction: A congenital short QT interval constitutes a new primary electrical abnormality associated with syncope and/or sudden cardiac death. We report on the initial use of implantable cardioverter defibrillator (ICD) therapy in patients with inherited short QT interval and discuss sensing abnormalities and detection issues.

Methods and Results: In five consecutive patients from two unrelated European families who had structurally normal hearts, excessively shortened QT intervals, and a strong positive family history of sudden cardiac death, ICDs were placed for primary and secondary prevention. Mean QT intervals were 252 ± 13 ms (QTc 287 ± 13 ms). Despite normal sensing behavior during intraoperative and postoperative device testing, 3 of 5 patients experienced inappropriate shock therapies for T wave oversensing 30 ± 26 days after implantation. Programming lower sensitivities and decay delays prevented further inappropriate discharges.

Conclusion: The congenital short QT syndrome constitutes a new clinical entity with an increased risk for sudden cardiac death. Currently, ICD treatment is the only therapeutic option. In patients with short QT interval and implanted ICD, increased risk for inappropriate therapy is inherent due to the detection of short‐coupled and prominent T waves. Careful testing of ICD function and adaptation of sensing levels and decay delays without sacrificing correct arrhythmia detection are essential. (J Cardiovasc Electrophysiol, Vol. 14, pp. 1273‐1277, December 2003)
Delineation of Intra‐Atrial Reentrant Tachycardia Circuits After Mustard Operation for Transposition of the Great Arteries Using Biatrial Electroanatomic Mapping and Entrainment Mapping
Authors: ZRENNER BERNHARD , DONG JUN , SCHREIECK JÜRGEN , NDREPEPA GJIN , MEISNER HANS , KAEMMERER HARALD , SCHÖMIG ALBERT , HESS JOHN , SCHMITT CLAUS
Published: December 2003

Introduction: Intra‐atrial reentrant tachycardia (IART) circuits after Mustard operation remain incompletely understood due to the complex atrial anatomy after extensive surgical procedures. The aim of this study was to delineate IART circuits and their relations to the individual anatomic boundaries in Mustard patients.

Methods and Results: Twelve patients (10 men and 2 women; age 29 ± 4.6 years) with atrial tachyarrhythmias after Mustard operation were included in this study. During 14 IARTs and 2 focal atrial tachycardias, electroanatomic mapping and entrainment mapping were performed in both the systemic venous atrium and the pulmonary venous atrium. The latter was accessed via a retrograde transaortic approach. Thirteen IARTs used a single‐loop reentrant circuit, and 1 IART used a dual‐loop reentrant circuit. Ten (77%) of 13 single‐loop reentrant circuits used the tricuspid annulus (TA) as their central barrier. The remaining 3 IARTs rotated around the inferior vena cava (IVC) (n = 2) or ostium of the right upper pulmonary vein (n = 1). In 6 (60%) of the 10 peritricuspid IARTs, both pulmonary venous atrium and systemic venous atrium components of the mid‐portion of the TA‐IVC isthmus were demonstrated to be part of the reentry. Overall, 12 (86%) of 14 IARTs in 10 patients were successfully ablated by bridging two barriers that constrained the reentrant circuit. Eight (80%) of 10 peritricuspid circuits were abolished by linear ablation connecting the TA to the IVC (n = 4), incisional scar (n = 2), patch (n = 1), and atriotomy (n = 1).

Conclusions: In Mustard patients, the TA serves as the most frequent central barrier of IART. Biatrial electroanatomic mapping combined with entrainment mapping facilitates delineation of IART circuits in relation to their anatomic barriers and enables the design of individual ablation strategies to achieve high success. (J Cardiovasc Electrophysiol, Vol. 14, pp. 1302‐1310, December 2003)
Magnetic Electroanatomic Mapping of an Atrial Tachycardia Requiring Ablation Within the Coronary Sinus
Authors: NAVARRETE ANTONIO J. , ARORA RISHI , HUBBARD JOYCE E. , MILLER JOHN M.
Published: December 2003

We describe a focal atrial tachycardia (AT) originating from the region of the inferoposterior mitral annulus in which ablation at the site of earliest endocardial activation during AT was unsuccessful. Three‐dimensional electroanatomic mapping identified the earliest atrial activation within the coronary sinus. Radiofrequency energy delivered at this site within the CS terminated this tachycardia without any complications, suggesting an origin within the CS. To our knowledge, this is the first time a three‐dimensional, high‐density activation map of such a tachycardia has been reported. (J Cardiovasc Electrophysiol, Vol. 14, pp. 1361‐1364, December 2003)
Role of Compact Node and Posterior Extension in Direction‐Dependent Changes in Atrioventricular Nodal Function in Rabbit
Authors: CLAUDE REID MARIE , BILLETTE JACQUES , KHALIFE KARIM , TADROS RAFIK
Published: December 2003

Introduction: AV nodal conduction properties differ in the anterograde versus the retrograde direction. The underlying substrate remains unclear. We propose that direction‐dependent changes in AV nodal function are the net result of those occurring in the slow and fast pathways.

Methods and Results: Anterograde and retrograde AV nodal properties were determined with a premature protocol before and after posterior extension (slow pathway) ablation, and before and after upper compact node (fast pathway) ablation. Each ablation was performed in a different group of six rabbit heart preparations. In control, nodal minimum conduction time (NCTmin) and effective refractory period (ERPN) typically were longer, and maximum conduction time (NCTmax) was shorter in the retrograde compared to the anterograde direction. Posterior extension ablation prolonged anterograde ERPN from 91 ± 10 ms to 141 ± 15 ms (P < 0.01) and shortened NCTmax from 150 ± 13 ms to 82 ± 7 ms (P < 0.01) but did not affect retrograde conduction. Thus, the posterior extension normally contributes to the anterograde but not retrograde recovery curve. Compact node ablation prolonged anterograde conduction (NCTmin increased from 57 ± 2 ms to 73 ± 7 ms, P < 0.01) but did not alter ERPN and NCTmax. This ablation abolished retrograde conduction in two preparations and resulted in retrograde slow pathway conduction in four, the latter being interrupted by posterior extension ablation. Thus, the compact node accounts for the baseline of the recovery curve in both directions. Ablation of the compact node results in anterograde slow pathway conduction over the entire cycle length range and may result in retrograde slow pathway conduction.

Conclusion: Direction‐dependent properties of the AV node arise from those of the compact node‐based fast pathway and posterior extension‐based slow pathway. Normal AV node has bidirectional dual pathways. (J Cardiovasc Electrophysiol, Vol. 14, pp. 1342‐1350, December 2003)
Mechanisms of Atrial Fibrillation
Authors: WALDO ALBERT L.
Published: December 2003

Based on experimental studies in the canine heart and an early computer model, atrial fibrillation (AF) has been thought to be due to multiple reentrant wavelets. However, subsequent studies in animal models are most consistent with a mechanism of AF due to a stable reentrant circuit of short cycle length or unstable reentrant circuits of short cycle length that drive the atria so fast that much or most of the atrial tissue manifests fibrillatory conduction. Limited mapping studies in patients during open heart surgery and during electrophysiologic studies using endocardial catheter electrodes also are most consistent with the concept of a driver, seemingly most often a focus in or near one or more of the pulmonary veins, precipitating and maintaining AF. However, a precise understanding of the mechanism(s) of AF in patients is not yet available. (J Cardiovasc Electrophysiol, Vol. 14, pp. S267‐S274, December 2003, Suppl.)
Clinical Experience with Dofetilide in the Treatment of Patients with Atrial Fibrillation
Authors: PRYSTOWSKY ERIC N. , FREELAND SCOTT , BRANYAS NANCY A. , RARDON DAVID P. , FOGEL RICHARD I. , PADANILAM BENZY J. , RIPPY JANET S.
Published: December 2003

Introduction: Dofetilide is the newest drug approved by the United States Food and Drug Administration for the treatment of patients with atrial fibrillation (AF). Few data on the efficacy and safety of dofetilide in a diverse group of patients are available. The aim of this study was to evaluate the results of dofetilide in a consecutive series of 69 patients with AF.

Methods and Results: Sixty‐nine patients with persistent (n = 53) or paroxysmal (n = 16) AF were administered dofetilide in‐hospital. Prior to starting dofetilide, all patients had been adequately anticoagulated, and concomitant agents contraindicated in the presence of dofetilide were discontinued. Heart rhythms were monitored continuously by telemetry in all patients. The initial dose, which was determined using the Cockroft‐Gault calculated creatinine clearance, was 500 μg bid, 250 μg bid, and 125 μg bid in 51, 13, and 5 patients, respectively. Reductions in subsequent dosage occurred in 12 patients, 4 for QT prolongation. Dofetilide was discontinued in‐hospital in 7 patients, 2 for adverse arrhythmic events and 3 for unacceptable QT prolongation. Twenty‐seven (63%) of 43 patients in AF converted spontaneously to sinus rhythm. Fifty‐eight patients were discharged receiving dofetilide treatment and were followed as outpatients for 21 ± 7 months. One third of patients continued to take dofetilide at 1 year. One patient had a cardiac arrest 1 day after hospital discharge.

Conclusion: Dofetilide is a well‐tolerated antiarrhythmic drug with a high conversion rate of AF to sinus rhythm. One third of patients maintained sinus rhythm at 1 year. Proarrhythmia can occur and initiation of therapy must be performed in‐hospital. (J Cardiovasc Electrophysiol, Vol. 14, pp. S287‐S290, December 2003, Suppl.)
Atrial Fibrillation in Heart Failure:
Authors: NACCARELLI GERALD V. , HYNES B. JOHN , WOLBRETTE DEBORAH L. , BHATTA LUNA , KHAN MAZHAR , SAMII SORAYA , LUCK JERRY C.
Published: December 2003

Atrial fibrillation and congestive heart failure are commonly occurring cardiac disorders that often exist concomitantly. The prognostic significance of the presence or absence of atrial fibrillation, as an independent risk factor, in patients with heart failure remains controversial. Antiarrhythmic drugs with good hemodynamic profiles and neutral effects on survival are preferred treatments for converting atrial fibrillation and maintaining sinus rhythm. Other standard therapies for congestive heart failure, such as angiotensin‐converting enzyme inhibitors, angiotensin receptor blockers, and beta‐blockers also have a role in the treatment of these coexisting disease states. The article presents an overview of atrial fibrillation in patients with heart failure and reviews the prevalence, prognostic significance, and efficacy of various antiarrhythmic agents for the conversion and maintenance of sinus rhythm. (J Cardiovasc Electrophysiol, Vol. 14, pp. S281‐S286, December 2003, Suppl.)
Overview of the Management of Atrial Fibrillation:
Authors: KOWEY PETER R. , YAN GAN‐XIN , DIMINO TARA L. , KOCOVIC DUSAN Z.
Published: December 2003

There are three fundamental approaches to the management of atrial fibrillation (AF): rate control, rhythm control, and anticoagulation. Selecting a course of treatment requires a thorough knowledge of these therapeutic alternatives. This article explores treatment options, including the relative benefits of rate control versus rhythm control, which are complicated by the lack of highly effective and safe antiarrhythmic drugs. Anticoagulation is also an important issue in AF management, and warfarin effectively reduces the incidence of thromboembolic events in AF patients. The use of warfarin, however, presents its own complications. We conclude that individualization of therapy is paramount when treating AF. (J Cardiovasc Electrophysiol, Vol. 14, pp. S275‐S280, December 2003, Suppl.)
Initiation and Monitoring of Class III Antiarrhythmic Agents
Authors: FREELAND SCOTT , WORTHY CHRISTINE , ZOLNIERZ MICHAEL
Published: December 2003

Dofetilide is a Class III antiarrhythmic agent that is approved by the United States Food and Drug Administration (FDA) for use in the conversion of atrial fibrillation, as well as in the maintenance of normal sinus rhythm. Because of the risk of torsades de pointes associated with dofetilide, the FDA mandated in‐hospital initiation of therapy and initially restricted dofetilide's availability to institutions and prescribers who completed appropriate educational forums. The use of dofetilide within health care systems requires specific procedures for prescribing, dispensing, and monitoring, as well as a format for educating personnel who will be involved in the care of these patients. Several models have demonstrated success in initiating dofetilide and are also used for sotalol, which also can cause torsades de pointes. The utilization of nonphysician personnel, such as nurse practitioners and clinical pharmacists, in conjunction with a team approach were essential components for the success of these models. Preprinted order forms or procedural guidelines, as well as computer‐assisted dosing programs, can be utilized to prevent inappropriate or miscalculated dosing of these agents, which potentially can cause life‐threatening ventricular arrhythmias. (J Cardiovasc Electrophysiol, Vol. 14, pp. S291‐S295, December 2003, Suppl.)
A Fundamental Equation for Trifluoromethane (R-23)
Authors: Penoncello Steven G. , Lemmon Eric W. , Jacobsen Richard T , Shan Zhengjun
Published: December 2003

A new formulation for the thermodynamic properties of trifluoromethane (R-23) is presented. The formulation is valid for single-phase and saturation states for temperatures from the triple point (118.02 K) to 475 K, pressures up to 120 MPa, and densities up to 24.31 mol/dm3. The formulation includes a fundamental equation and ancillary functions for the estimation of saturation properties. The experimental data used to determine the fundamental equation included pressure–density–temperature (p–ρ–T), isobaric heat capacity (cp–p–T), isochoric heat capacity (cν–ρ–T), saturation heat capacity (cσ), speed of sound (w–p–T), and vapor pressure. A nonlinear regression algorithm was used to determine the constants and exponents of various functions within the formulation. Experimental data and values computed using the formulation are compared to verify the uncertainties in the calculated properties. The formulation presented may be used to compute densities to within ±0.1%, heat capacities to within ±0.5%, speed of sound to within ±0.5%, and vapor pressures to within ±0.2%, except near the critical point.
Viscosity and pVT–Second Virial Coefficient of Binary Noble–Globular Gas and Globular–Globular Gas Mixtures Calculated by Means of an Isotropic Temperature-Dependent Potential
Authors: Zarkova L. , Hohm U. , Damyanova M.
Published: December 2003

This work presents results of an extension of our earlier studies of the transport and equilibrium properties of pure heavy globular gases. It demonstrates a simple and reliable procedure for estimating the equilibrium and transport properties of their mixtures using the pure gas potentials of interaction when there are no available experimental data. Here we consider binary gas mixtures of globular gases between themselves and with the noble gases as well. The gases involved are: BF3, CH4, CF4, SiF4, SiCl4, CCl4, SF6, MoF6, WF6, UF6, C(CH3)4, Si(CH3)4, Ar, Kr, and Xe. The calculations were performed by means of the so called isotropic temperature–dependent potential (ITDP) introduced by us earlier and applied to some binary mixtures (CH4–CF4, CH4–SF6, CF4–SF6). The CH4–CH4 and noble gases potentials of interactions have been determined in a (n−6) Lennard-Jones shape in the temperature range 200–1000 K by fitting a large number of viscosity and pVT–second virial coefficient data measured by different authors with different experimental techniques. The ITDP parameters of molecular gases were taken from the tables we have determined and published earlier [L. Zarkova and U. Hohm, J. Phys. Chem. Ref. Data 31, 183 (2002)]. Simple combination rules allow us to take into account the influence of the temperature on the thermophysical properties of the binary gas mixtures containing heavy globular molecules. Tables with potential parameters of equal and unequal particles and properties of the equimolar mixtures are given for all mixtures in the temperature range 200–900 (1000) K. The deviations between experimental and calculated viscosity and second virial coefficient data of some more examined mixtures permit to evaluate the quality of the proposed approach.
Single wall carbon nanotube fibers extruded from super-acid suspensions: Preferred orientation, electrical, and thermal transport
Authors: Zhou W. , Vavro J. , Guthy C. , Winey K. I. , Fischer J. E. , Ericson L. M. , Ramesh S. , Saini R. , Davis V. A. , Kittrell C. , Pasquali M. , Hauge R. H. , Smalley R. E.
Published: December 2003

Fibers of single wall carbon nanotubes extruded from super-acid suspensions exhibit preferred orientation along their axes. We characterize the alignment by x-ray fiber diagrams and polarized Raman scattering, using a model which allows for a completely unaligned fraction. This fraction ranges from 0.17 to 0.05±0.02 for three fibers extruded under different conditions, with corresponding Gaussian full widths at half maximum (FWHM) from 64° to 44°±2°. FWHM, aligned fraction, electrical, and thermal transport all improve with decreasing extrusion orifice diameter. Resistivity, thermoelectric power, and resonant-enhanced Raman scattering indicate that the neat fibers are strongly p doped; the lowest observed ρ is 0.25 mΩ cm at 300 K. High temperature annealing increases ρ by more than 1 order of magnitude and restores the Raman resonance associated with low-energy van Hove transitions, without affecting the nanotube alignment.
Feeding a sub-ns-risetime rectangular pulse onto a rod-shaped resistive high-voltage divider in risetime <2 ns
Authors: Zeng Zhengzhong , Ma Lianying
Published: December 2003

A simple and effective bridge-type feeding network consisting only of ordinary resistors and conductive wires is designed and tested which launches a 0.8 ns risetime, 40 ns width, and kV-level rectangular pulse from a coaxial cable onto a rod-shaped resistive high-voltage divider with risetime <2 ns with no significant distortion.
Analysis of shock wave measurements in water by a piezoelectric pressure probe
Authors: Grinenko A. , Gurovich V. Ts. , Krasik Ya. E. , Sayapin A. , Efimov S. , Felsteiner J.
Published: December 2003

Investigation of underwater electrical wire explosions occurring in the time scale of few microseconds requires a measurement of pressure waves with nanosecond rise time and microsecond fall time. Various types of pressure gauges are used for this purpose, however, none of them seems to be suitable for the task since the frequency range of the pressure waves lies between 107 and 109 Hz, whereas all types of mechanical gauges have a bandwidth below 107 Hz. Therefore, a mathematical processing of measurements is required for reconstruction of the actual pressure wave forms. In this article, a signal processing algorithm, based on energy conservation requirements and Fourier analysis, for reconstruction of the wave form of the pressure wave generated under water by electrical explosion of wires is proposed. The gauge used in the experiments is a PCB 119A12 type pressure gauge with a bandwidth below 1 MHz produced by Piezo-Electronics, Inc. Pressure waves were produced by underwater electrical explosion of a thin wire made of Cu by a current pulse with an amplitude of 30–60 kA having a rise time of a 3 μs. It is shown that the error of the gauge in the measurement of the peak pressure is more than 100%, which leads to an error in the estimation of the energy of almost 300%.
Cool pulsed molecular microbeam
Authors: Zhao Bum Suk , Castillejo Marta , Chung Doo Soo , Friedrich Bretislav , Herschbach Dudley
Published: December 2003

We produce a cool pulsed supersonic molecular beam of CaF radicals essentially without recourse to pumping. The radicals are generated by laser ablating a solid precursor target in a small ablation cell of volume of about 0.01 cm3. The target is ablated through a 750 μm orifice by a pulsed Nd:YAG laser. The ablation plume supersonically expands into a vacuum chamber and cools the initially hot CaF molecules seeded in it. We enhance the supersonic character of the expansion by feeding into the ablation cell about 10 Torr of He, Ar, or Xe carrier gas. The CaF molecules are probed by time-dependent laser absorption spectroscopy. With a Xe carrier, about 1012 CaF molecules are found to be seeded in a single pulse and cooled down to a terminal translational temperature of about 140 K. We expect that a wide variety of species, including highly unstable ones, will be amenable to forming such a cool intense molecular microbeam, to the benefit of spectroscopy, reaction dynamics, and microfabrication.
X-ray absorption fine structure spectrometer using a compact superconducting synchrotron radiation source
Authors: Ozutsumi Kazuhiko , Handa Katsumi
Published: December 2003

We have constructed an x-ray absorption fine structure (XAFS) spectrometer at BL-4 using the compact superconducting synchrotron radiation (SR) source at Ritsumeikan University. BL-4 is simply designed and consists of a slit, a double-crystal monochromator, and two detectors. The mechanical movement of the monochromator is in the range from 15° to 75°. By using Si(220), Ge(220), and InSb(111) crystals, the XAFS spectrometer covers the K-edge absorption energies of elements from silicon to zinc under atmospheric pressure. The incident x-ray intensity is measured by an ionization chamber with a path length of 4.5 cm. The transmitted x-ray intensity after passing through a sample is monitored by either an ionization chamber with a path length of 31 cm or a scintillation counter. The steep decrease of x-ray intensities above 5 keV is characteristic of the spectrum of photons emitted from the compact SR source and the photon flux at 10 keV is two to three orders of magnitude smaller than that at 5 keV. Hence, the contamination of higher-order harmonics is negligible above 5 keV. The double-crystal monochromator should be detuned only in measuring K-edge XAFS spectra of K, Ca, and Sc by using Si(220) or Ge(220). Suitable gases for two ionization chambers are easily selected only based on the detection efficiency of He(100%), N2(100%), N2(85%)+Ar(15%), N2(50%)+Ar(50%), and Ar(100%) gases. The photon flux passing through a 2 mm×9 mm aperture is estimated from the ion current of the ionization chamber. Though the values normalized to 1 mm2 are a few orders of magnitude smaller than those of BL7C at the Photon Factory, it turned out that measurements of XAFS spectra of good quality are very easy to obtain from 1.7 to 10.5 keV by using the spectrometer at BL-4.
Scenario for time evolution of insulator charging under various focused electron irradiations
Authors: Cazaux Jacques
Published: December 2003

The expected time evolution of the secondary electron emission (SEE) yield, δ, and charging of insulators irradiated with keV electron probes of various sizes is deduced from the use of basic laws of electrostatics. Simple models of trapped charge distributions permit, next, quantitative estimates. With respect to the linear increase of δ from 0 towards its nominal value, δ0, the initial phase is characterized by a deficit of δ for incident spots in the submicron range and incident charge of a few 102 primary electrons (PEs). This deficit occurs even when charging is as a whole negative and it results from a partial mirror effect for the less energetic δP secondary electrons (SEs) (directly excited by the PEs) combined to attraction of δBSE (excited by the backscattered electrons) towards the central spot while the more energetic δp SEs are successively focused and next defocused. The next phase starts for incident charges in the pC range and it concerns the evolution of the total yield, δ+η from its nominal value up to the unity. Besides the increase of the SEE yield, the external slowing down of the PEs plays the main role in the compression of the distribution of newly trapped electrons. The main dynamical aspects of the internal field are also established and its influence on the trapped charge distribution is easily deduced. The present analysis is supported by some published data and the consequences concern any type of insulating material irradiated with defocused probes and “short” pulse excitation (for δ0 measurements) or stationary fine probes (for the investigation of the space charge effect by the mirror method) or scanning beams (in scanning electron microscopy).
Heteroepitaxial growth behavior of Mn-doped ZnO thin films on Al2O3 (0001) by pulsed laser deposition
Authors: Kim Sang Sub , Moon Jong Ha , Lee Byung-Teak , Song Oh Sung , Je Jung Ho
Published: December 2003

Heteroepitaxial growth behavior of Mn-doped ZnO thin films (Zn1−xMnxO) on Al2O3 (0001) substrates by pulsed laser deposition was investigated particularly as a function of Mn content (0.00⩽x⩽0.35) using synchrotron x-ray scattering and atomic force microscopy. The undoped ZnO film was grown epitaxially with a 30° rotation of ZnO basal planes with respect to the Al2O3 substrate while having a small amount of grains with another epitaxial relationship, i.e., the hexagon-on-hexagon growth. A small amount of Mn doping (x=0.05) not only greatly improved the atomic alignment both in the in-plane and in the out-of-plane directions, but also led to a singly oriented film by totally suppressing the hexagon-on-hexagon growth. With further incorporation of Mn into ZnO beyond that content, the epitaxial nature again deteriorated. The superior epitaxial growth of the film with an optimum Mn content is attributed to the formation of much larger grains in it. In addition, our Mn-doped ZnO thin films showed a paramagnetic behavior.
Bolometric technique for high-resolution broadband microwave spectroscopy of ultra-low-loss samples
Authors: Turner P. J. , Broun D. M. , Kamal Saeid , Hayden M. E. , Bobowski J. S. , Harris R. , Morgan D. C. , Preston J. S. , Bonn D. A. , Hardy W. N.
Published: December 2003

A novel low-temperature bolometric method has been devised and implemented for high-precision measurements of the microwave surface resistance of small single-crystal platelet samples having very low absorption, as a continuous function of frequency. The key to the success of this nonresonant method is the in situ use of a normal metal reference sample that calibrates the absolute rf field strength. The sample temperature can be controlled independently of the 1.2 K liquid-helium bath, allowing for measurements of the temperature evolution of the absorption. However, the sensitivity of the instrument decreases at higher temperatures, placing a limit on the useful temperature range. Using this method, the minimum detectable power at 1.3 K is 1.5 pW, corresponding to a surface resistance sensitivity of ≈1 μΩ for a typical 1 mm×1 mm platelet sample.
Experimental setup for calorimetric alternating current loss measurements on high-temperature superconductor tapes in applied longitudinal magnetic fields carrying transport currents at variable temperatures
Authors: Wass Torbjörn , Hörnfeldt Sven
Published: December 2003

In most power devices, the conductor is carrying an ac transport current while it is exposed to an ac magnetic field transverse to the current path. In certain applications, such as multilayer power cables or the control winding in a controllable reactor, the conductors are exposed to a magnetic field component parallel with the current path that is longitudinal to the tape axis. An experimental setup to measure the losses at a different longitudinal magnetic field, transport currents, frequency, and temperature is presented. The system is based on a calorimetric measuring method. Examples are given of power loss measurements on multifilamentary Bi 2223 tapes at different longitudinal ac magnetic fields 0–250 mT peak value, frequencies 0–1000 Hz, ac transport currents 0–70 A peak value, and temperatures 55–85 K. The calorimetric technique presented is fast, accurate, and capable of measuring losses between 0.5–100 mW/m. The data obtained from the apparatus can provide an improved base for the design of power devices.
Measuring thermal conductivity in extreme conditions: Sub-Kelvin temperatures and high (27 T) magnetic fields
Authors: van der Linden P. J. E. M. , Behnia K.
Published: December 2003

We present a one-heater-two-thermometer setup for measuring thermal conductivity and electric resistivity of a bulk sample at low temperatures down to 0.1 K and in magnetic fields up to 27 T. The design overcomes the difficulties emerging in the context of large water-cooled resistive magnets.
Electrical and thermal modeling of the non-Ohmic differential conductance in a tunnel junction containing a pinhole
Authors: Zhang Z.-S. , Rabson D. A.
Published: December 2003

To test the quality of a tunnel junction, one sometimes fits the bias-dependent differential conductance to a theoretical model, such as Simmons’s formula. Recent experimental work by Åkerman and collaborators, however, has demonstrated that a good fit does not necessarily imply a good junction. Modeling the electrical and thermal properties of a tunnel junction containing a pinhole, we extract an effective barrier height and effective barrier width even when as much as 88% of the current flows through the pinhole short rather than tunneling. A good fit of differential conductance to a tunneling form therefore cannot rule out pinhole defects in normal metal or magnetic tunnel junctions.
Simulation of hole phonon-velocity in strained Si/SiGe metal-oxide-semiconductor transistor
Authors: Payet Fabrice , Cavassilas Nicolas , Autran Jean-Luc
Published: December 2003

Hole phonon velocity in a strained Si inversion layer grown on a relaxed SiGe substrate has been theoretically investigated. We used: (i) a 20 band k.p Hamiltonian method for the valence-band structure calculation, (ii) a self-consistent Schrödinger and Poisson equations solver for the confined hole subband determination, (iii) a direct matrix Boltzmann transport equation solver including hole-phonon interactions for the carrier velocity estimation in the subband structure. The present work particularly focuses on the influence of SiGe alloy composition and strained Si layer thickness on the hole dynamic in the inversion layer. Our results highlight the linear slope of the hole velocity enhancement factor with strain in the Si layer. But at the same time, large strain facilitates transfer in the parasitic channel at the Si/SiGe interface for which the carrier mobility is highly degraded. Consequently, in order to optimize a p-channel transistor with Si layer strain on SiGe virtual substrate, a compromise must be found between mobility in Si layer and parasitic transfer phenomenon in this interface. Our results suggest that a 10 nm Si layer thickness strain on a relaxed Si0.7Ge0.3 allows one to take advantage of the strain-induced enhancements of carrier transport characteristics. At the same time this compromise is realistic from a technological point of view.
Characteristics of a stick waveguide resonator in a two-dimensional photonic crystal slab
Authors: Kim Se-Heon , Kim Guk-Hyun , Kim Sun-Kyung , Park Hong-Gyu , Lee Yong-Hee , Kim Sung-Bock
Published: December 2003

Optical loss and polarization characteristics of the photonic crystal stick waveguide resonator modes were investigated using both theory and experiment. A stick waveguide resonator with 12 missing air holes was found to have a very high Q(>3 800 000) mode originating from the lossless guided mode below the light line. Photoluminescence spectra show sharp resonance peaks at regular intervals in k space, satisfying the resonant condition. Linear polarizations parallel or perpendicular to the waveguide were observed, depending on the mode symmetry. This polarization selection is explained in terms of the far-field cancellation effect of the in-plane field components.
Effect of nonequilibrium ionization process on gain of neon-like argon x-ray laser
Authors: Masnavi Majid , Nakajima Mitsuo , Horioka Kazuhiko
Published: December 2003

In connection with fast plasma heating in capillary discharges, transient ionization effect on the gain of J=0→1 transition (λ=46.9 nm) in optically thin neon (Ne)-like argon (Ar IX) x-ray laser has been theoretically investigated using the reduced time-dependent collisional–radiative model. Results indicate that the gain value at nonequilibrium ionization regime is significantly affected by the relaxation process of different ionization states, and fast heating enables us to obtain higher gain compared with the steady-state plasma.
Broadband photoacoustic spectroscopy using a free-electron laser
Authors: Gómez Rivas J. , Sprik R.
Published: December 2003

Using the pulsed structure of the radiation generated by a free-electron laser, we demonstrate the capabilities of this sort of laser to perform broadband photoacoustic spectroscopy. In particular, we have measured the photoacoustic spectrum of powdered samples formed by micron-sized particles of germanium in the wavelength range of 4.5–8 μm. Two absorption bands at 6 and 6.9 μm are associated with hydrocarbon impurities introduced during the sample preparation. Independent measurements of the diffusive transmission and reflection confirm the presence of this absorption.
Automatic system to control the operation of an extended cavity diode laser
Authors: Allard F. , Maksimovic I. , Abgrall M. , Laurent Ph.
Published: December 2003

This article describes an automatic system that permanently keeps an extended cavity diode laser (ECDL) frequency locked to a cesium line (852 nm). The ECDL has a new architecture based on an intracavity étalon. The laser power is 30 mW and the linewidth is narrower than 50 kHz. Two acousto-optic modulators finely change the laser frequency and optical power. The electronic control is composed of a computer, microcontrollers, digital analog converters, and direct digital synthesizers. The computer searches the ECDL parameters to tune it to the Cs line and closes the servoloop. It permanently checks the servoloop and relocks the laser if necessary. Both acousto-optic modulators are driven in real time by microcontrollers. They are programed in order to control the laser power and frequency with a predefined time sequence. This system, especially developed for an atomic fountain, can be easily adapted to a wide range of applications.
Converting a fluorescence spectrophotometer into a three-channel colorimeter for color vision research
Authors: Pardo P. J. , Pérez A. L. , Suero M. I.
Published: December 2003

An old fluorescence spectrophotometer was recycled to make a three-channel colorimeter. The various modifications involved in its design and implementation are described. An optical system was added that allows the fusion of two visual stimuli coming from the two monochromators of the spectrofluorimeter. Each of these stimuli has a wavelength and bandwidth control, and a third visual stimulus may be taken from a monochromator, a cathode ray tube, a thin film transistor screen, or any other light source. This freedom in the choice of source of the third chromatic channel, together with the characteristics of the visual stimuli from the spectrofluorimeter, give this design a great versatility in its application to novel visual experiments on color vision.
Surface-state origin for the blueshifted emission in anodically etched porous silicon carbide
Authors: Rittenhouse Tilghman L. , Bohn Paul W. , Hossain Tim K. , Adesida Ilesanmi , Lindesay James , Marcus Alfred
Published: December 2003

Anodic etching of SiC yields a highly monodisperse distribution of nanometer dimension porous structures which extend to a significant depth. Cathodoluminescence (CL) studies of the porous layers yield luminescence peaks in the UV region, above the band gap energy of bulk SiC. Higher etching current densities produce porous silicon carbide (PSiC) with peak CL emission wavelengths deeper in the ultraviolet. Photoluminescence (PL) is also blueshifted in anodically etched PSiC, although not to the extent of the CL emission, suggesting that different emissive states are accessed in CL and PL. Raman investigations of the polar A1 LO mode, which couples strongly to the macroscopic electric field accompanying the LO phonon, were conducted in an attempt to discern whether quantum confinement effects could effectively explain the blueshifted emission. The principal feature of the Raman spectra was a significant low-frequency shoulder on the A1 LO mode, the magnitude of which correlates with the magnitude of the blueshift in PL and the intensity of the blueshifted CL emission. The shoulder was fit quantitatively with a model incorporating the effects of extraordinary LO modes and longitudinal and transverse Fröhlich modes. The Fröhlich mode widths derived from the fit are too wide to be due solely to Fröhlich modes and likely indicate the combined effects of diffuse scattering, broadening of spectral lines, and violation of the symmetry selection rules. The preponderance of the evidence, especially the inability to fit the low-frequency shoulder in the Raman spectra with a phonon confinement model, support an interpretation in which defect structures or surface states are responsible for the UV emission.
Combinatorial fabrication and studies of bright white organic light-emitting devices based on emission from rubrene-doped 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl
Authors: Li G. , Shinar J.
Published: December 2003

Very bright and efficient white multilayer organic light-emitting devices based on orange-emitting 2–10-nm-thick layers of 0.25 and 0.5 wt % rubrene-doped 4,4′-bis(2,2′-diphenylvinyl)-1,1′biphenyl are described. The color coordinates of all but one of the devices are well within the white region at 6–12 V, corresponding to a dynamic white brightness range of 30 dB. Their highest brightness Lmax was over 74 000 Cd/m2; in all devices Lmax exceeded 50 000 Cd/m2. The maximum efficiencies were 11.0 Cd/A, 6.0 lm/W, and 4.6% at 5.8 V, 0.6 mA/cm2, and 68 Cd/m2 in the 0.25 wt %, 2-nm-thick doped layer device. The color variation is attributed to either emission from different zones in devices with a thin doped layer, or saturation of emission sites due to relatively light doping.
Photoemission study of Cu deposition on molecular-beam-epitaxy-grown ZnS(001)
Authors: Zhang L. , Szargan R. , Chassé T.
Published: December 2003

The formation, the chemical and electronic properties, and the thermal stability of the Cu/ZnS(001) interface were investigated by x-ray photoelectron spectroscopy, x-ray fluorescence spectroscopy, and low energy electron diffraction (LEED). ZnS(001) films with 16 ML thickness (4.3 nm), grown on bulk GaP(001) were used as a substrate for Cu deposition. During the room-temperature deposition of the Cu film, the initial submonolayer Cu atoms react with ZnS and the reaction is confined to the interface. Beyond 1 ML the Cu starts to display a metallic character. The Cu deposition induced a downward band bending of ZnS. In the S L2,3 emission spectrum, the Cu deposition results in a significant suppression of the Zn 3d-related doublet and creates a component at about 3.6 eV binding energy in the upper valence band. After annealing of room-temperature-deposited Cu films at temperatures higher than 220 °C, as well as Cu deposition at 320 °C, the signals of Ga 2p photoelectrons reappear, as a result of Cu atoms diffusing into the substrate and reacting with GaP. From LEED observation and attenuation of Zn 2p3/2 intensity, we may conclude that the Cu film grows in an island mode at room temperature, whereas a partially ordered arrangement is adopted at the ZnS(001) surface following Cu deposition at 320 °C.
Two lasing thresholds in semiconductor lasers with a quantum-confined active region
Authors: Asryan Levon V. , Luryi Serge
Published: December 2003

We show that the free-carrier-density dependence of internal optical loss gives rise, in general, to the existence of a second lasing threshold above the conventional threshold. Above the second threshold, the light-current characteristic is two-valued up to a maximum current at which the lasing is quenched.
Calculated and measured transmittance of a tunable metallic photonic crystal filter for terahertz frequencies
Authors: Drysdale Timothy D. , Blaikie Richard J. , Cumming David R. S.
Published: December 2003

A tunable metallic photonic crystal filter with a mechanical tuning mechanism is demonstrated. The performance is predicted with rigorous full-vector electromagnetic simulations (finite-difference time domain). A prototype has been built and characterized in the W band (70–110 GHz) using a vector network analyzer configured for free-space measurement of S parameters. The measured filter’s passband has a quality factor of 11, a tuning range of 3.5 GHz, and insertion loss of only 1.1–1.7 dB. Device fabrication is straightforward, yielding an inexpensive, robust and compact tunable filter.
Solid-like dynamics in ultrathin films of polymeric liquids
Authors: Singh Gaurav , Saraf Ravi F. , Martin Yves
Published: December 2003

In this letter, we demonstrate that, at mesoscales, nonferroelectric liquid films of poly(dimethyl siloxane) exhibit significant electrostriction not present in the corresponding bulk state. Remarkably, the observed electrostrictive effect has a response time <20 μs in contrast to >5 ms recorded in conventional bulk (ferroelectric) polymers. The emergence of this fast electrostrictive strain in thin films is explained in terms of the amalgamation of two contrasting dynamic features—the influence of a highly mobile, viscous layer (at the air/film interface) on the less-mobile, but fast responding, solid-like layer at the film/substrate interface. The effect is observed for thickness below 200 nm.
Magnetoluminescence properties of GaAsSbN/GaAs quantum well structures
Authors: Senger R. T. , Bajaj K. K. , Jones E. D. , Modine N. A. , Waldrip K. E. , Jalali F. , Klem J. F. , Peake G. M. , Wei X. , Tozer S. W.
Published: December 2003

We report a measurement of the variation of the diamagnetic shift of a heavy-hole exciton in a single coherently strained GaAs0.685Sb0.3N0.015/GaAs quantum well as a function of magnetic field up to 32 T at 1.3 K using photoluminescence spectroscopy. The excitons are known to be localized in this alloy system. This localization is simulated by assuming that the hole is completely immobilized, i.e., its mass is infinite. Using this model we have calculated the variation of the diamagnetic shift with magnetic field in this quantum well structure following a variational approach. We find that the observed variation of the diamagnetic shift with magnetic field agrees quite well with that calculated when the mass of the conduction electron in the well is assumed to be 0.09 m0, about 50% larger than in GaAs0.7Sb0.3, an increase similar to that found in GaAsN for the same nitrogen composition.
Midinfrared “W” diode lasers with improved electrical characteristics
Authors: Kim M. , Bewley W. W. , Lindle J. R. , Kim C. S. , Vurgaftman I. , Meyer J. R. , Kim J. G. , Martinelli R. U.
Published: December 2003

Midinfrared “W” quantum-well diode lasers with reduced turn-on voltages are reported. Devices with coated facets operated in continuous-wave mode up to 195 K, where the emission wavelength was 3.56 μm. At 78 K, the threshold current density was 67 A/cm2, the maximum output power was 198 mW, and the slope efficiency was 106 mW/A.
S–d
exchange interaction in GaN:Mn studied by electron paramagnetic resonance
Authors: Wolos Agnieszka , Palczewska Maria , Wilamowski Zbyslaw , Kaminska Maria , Twardowski Andrzej , Bockowski Michal , Grzegory Izabella , Porowski Sylwester
Published: December 2003

We present the electron paramagnetic resonance investigations of GaN:Mn bulk crystals. The performed measurements revealed the Korringa scattering as the dominant spin relaxation mechanism in the investigated highly n-type GaN:Mn samples. The temperature dependence of the spin relaxation time determines the effective s–d exchange constant for such crystals {N0α}=14 meV. Weak exchange interaction between Mn2+ and GaN band electrons excludes carrier mediation as an origin of high-temperature ferromagnetism in n-type GaMnN.
Ferromagnetism in cobalt-implanted ZnO
Authors: Norton D. P. , Overberg M. E. , Pearton S. J. , Pruessner K. , Budai J. D. , Boatner L. A. , Chisholm M. F. , Lee J. S. , Khim Z. G. , Park Y. D. , Wilson R. G.
Published: December 2003

The magnetic and structural properties of cobalt-implanted ZnO single crystals are reported. High-quality, (110)-oriented single-crystal Sn-doped ZnO substrates were implanted at ∼350 °C with Co to yield transition metal concentrations of 3–5 at. % in the near-surface (∼2000 Å) region. After implantation, the samples were subject to a 5 min rapid thermal annealing at 700 °C. Magnetization measurements indicate ferromagnetic behavior, with hysteresis observed in the M vs H behavior at T=5 K. Coercive fields were ⩽100 Oe at this measurement temperature. Temperature-dependent magnetization measurements showed evidence for ordering temperatures of >300 K, although hysteresis in the M vs H behavior was not observed at room temperature. Four-circle x-ray diffraction results indicate the presence of (110)-oriented hexagonal phase Co in the ZnO matrix. From the 2θ full width at half maximum (FWHM) of the Co (110) peak, the nanocrystal size is estimated to be ∼3.5 nm, which is below the superparamagnetic limit at room temperature. In-plane x-ray diffraction results show that the nanocrystals are epitaxial with respect to the ZnO host matrix. The magnetic properties are consistent with the presence of Co nanocrystals, but do not preclude the possibility that a component of the magnetism is due to Co substitution on the Zn site in the ZnO matrix.
Formation and optical properties of CdTe self-assembled pyramids with quantum states grown on ZnTe buffer layers
Authors: Lee E. H. , Lee K. H. , Kim J. S. , Park H. L. , Kim T. W.
Published: December 2003

Atomic force microscopy (AFM) and photoluminescence (PL) measurements were carried out to investigate the structure and to determine the electron activation energy in CdTe/ZnTe pyramids grown by using molecular beam epitaxy and atomic layer epitaxy methods. The AFM images showed that self-assembled CdTe pyramids were formed on ZnTe buffer layers. The PL spectra showed that the formed CdTe pyramids had quantum states and that the excitonic peak corresponding to the transition from the ground electronic subband to the ground heavy-hole band (E1–HH1) in the CdTe/ZnTe pyramids was shifted to higher energy in comparison with that in CdTe/ZnTe quantum dots (QDs). The activation energy of the electrons confined in the CdTe pyramids, as obtained from the temperature-dependent PL spectra, was higher than that in CdTe QDs. These results can help improve an understanding of the formation and optical properties in self-assembled CdTe pyramids with quantum states.