bluuebunny/crossref_metadata_2025 huggingface dataset:
Principal Component Analysis of the T Wave in Patients with Chest Pain and Conduction Disturbances
Authors: KESEK MILOS , JERNBERG TOMAS , LINDAHL BERTIL , XUE JOEL , ENGLUND ANDERS
Published: October 2004

There is a need for markers reflecting the increased risk in patients with conduction disturbances. Conduction disturbances presumably cause inhomogeneous repolarization that may create an arrhythmogenic substrate. In patients with normal conduction, parameters derived from principal components analysis (PCA) of the T wave contain prognostic information. The nondipolar PCA components are assumed to reflect repolarization inhomogeneity. This study examined the PCA parameters in relation to conduction disturbances. PCA was performed on continuously recorded 12‐lead ECGs in 800 patients with chest pain and nondiagnostic ECG on admission. The patients with conduction disturbance on admission were classified into separate groups and related to comparison groups without conduction disturbance recruited from the same series. For each patient, the dipolar and nondipolar components were quantified by medians of the ratio of the two largest eigenvalues (S2/S1 Median), the residue that summarizes the eigenvalues S4–S8 (TWRabsMedian) and the ratio of this residue to the total power of the T wave (TWRrelMedian). The parameters were assessed with respect to common clinical and ECG parameters, discharge diagnosis, and total mortality during a 35‐month follow‐up. TWRabsMedian increased with increasing conduction disturbance. In 135 patients with conduction disturbances, ROC curves for TWRabsMedian as indicator of mortality exhibited areas under a curve of 0.66, 0.65, and 0.56 at 6‐month, 24‐month, and 35‐month follow‐up. Conduction disturbances were associated with increased nondipolar PCA component and, thus, with increased repolarization inhomogeneity. The nondipolar PCA component contained a moderate amount of prognostic information not present in a simple ECG diagnosis of a conduction disturbance.
Long‐Term Performance of Transvenous, Steroid‐Eluting, High Impedance, Passive‐Fixation Ventricular Pacing Leads
Authors: YEH KUAN‐HUNG , WANG CHUN‐CHIEH , WEN MING‐SHIEN , CHOU CHUNG‐CHUAN , YEH SAN‐JOU , WU DELON
Published: October 2004

The long‐term performance of two high impedance, steroid‐eluting, passive‐fixation ventricular leads, porous platinum iridium electrode CPI Selute Picotip 4035 (131 patients), and platinized platinum electrode Medtronic Capsure Z 5034 (57 patients), was compared with one conventional 8.0‐mm2 porous platinum iridium electrode CPI Selute 4285 (38 patients). The mean follow‐up period was 28 ± 14 months. Capture threshold, R wave amplitude, and pacing impedance were measured at the time of implantation, immediately after implantation, 1 week, 1, 3, and 6 months after implantation and then every 6 months thereafter. The two high impedance leads revealed a higher sensing slew rate than the conventional lead, the R wave amplitude was similar among the three groups, but the voltage threshold at 0.5‐ms pulse width was significantly higher in porous platinum iridium groups at the time of implantation. During follow‐up, the conventional lead revealed a significantly higher R wave amplitude within the first 3 months, however, this pattern disappeared after 3 months. Pacing impedance was significantly higher in the high impedance porous platinum iridium electrode groups. Voltage threshold at 0.5‐ms pulse width was similar among the three groups in the first 3 months, however, it increased gradually and was significantly higher in porous platinum iridium electrode groups subsequently. The energy threshold at 0.5 ms was significantly lower in the two high impedance groups than the conventional group, but no difference was found in the two high impedance groups. Lead related complications were similar among the three groups. In conclusion, high impendence electrodes with different design and materials had different properties; platinized platinum electrode showed a lower pacing impedance but had a more stable long‐term capture threshold as compared to the porous platinum iridium electrode. Further studies are mandatory for the development of an ideal pacing lead.
The Role of Angiotensin Receptor Blockers and/or Angiotensin Converting Enzyme Inhibitors in the Prevention of Atrial Fibrillation in Patients with Cardiovascular Diseases:
Authors: MADRID ANTONIO H. , PENG JIAN , ZAMORA JAVIER , MARÍN IRENE , BERNAL ENRIQUE , ESCOBAR CARLOS , MUÑOS‐TINOCO CONCEPCIÓN , REBOLLO JOSÉ M.G. , MORO CONCEPCIÓN
Published: October 2004

The inhibition of the renin‐angiotensin system has demonstrated both experimental and clinical effects in preventing atrial fibrillation. However, there is still uncertainty about the role of these drugs in clinical practice. The objective of this review has been to assess the effects of angiotensin II type‐1 receptor blockers (ARBs) and/or angiotensin converting enzyme inhibitors (ACEIs) for preventing atrial fibrillation. We searched the Cochrane controlled Trials Register (Cochrane Library Issue 4, 2002), MEDLINE (January 1980 to November 2003), EMBASE (January 1980 to November 2003) and reference list of articles. We also contacted manufacturers and researchers in the field. Selection criteria: We conducted a meta–analysis of all randomized controlled clinical trials that compared ARBs and/or ACEIs with either placebo or conventional therapy in patients with either hypertension, heart failure, ischemic heart disease, or diabetes mellitus. The pooled outcome was the development of new onset atrial fibrillation. Two reviewers independently assessed trial quality and extracted data. In some cases, the study authors were contacted for additional information. Seven trials involving a total of 24,849 patients were included (11,328 randomized to active therapy and 13,521 to control). There was a significant statistical difference in the pooled development of atrial fibrillation between the treatment and control group. (OR, 0.57; 95% CI, 0.39 to 0.82); test for overall effect z = 2.98 P = 0.003). Treatment with ACEIs/ARBs markedly reduces the risk of development or recurrence of atrial fibrillation.
Successful Catheter Ablation of Atrial Tachycardia Originating Near the Atrioventricular Node from the Noncoronary Sinus of Valsalva
Authors: TADA HIROSHI , NAITO SHIGETO , MIYAZAKI AKIHISA , OSHIMA SHIGERU , NOGAMI AKIHIKO , TANIGUCHI KOICHI
Published: October 2004

This report describes a patient who underwent RF catheter ablation of atrial tachycardia. Two applications of RF energy near the His‐bundle region transiently terminated the tachycardia. With detailed mapping at the aortic sinus of Valsalva using a retrograde transaortic approach, the earliest atrial activation was found in the noncoronary sinus of Valsalva. Complete elimination of the tachycardia was achieved with RF energy application from this site.
Malfunction of a Biventricular Pacing Device?
Authors: EIDELMAN RACHEL S. , DIEGUEZ FRANCISCO J. , TOLENTINO ALFONSO , ZEBEDE JOSEPH
Published: October 2004

A patient with dilated cardiomyopathy and recurrent admissions for heart failure presented 3 days after implantation of a biventricular pacemaker to the emergency department. Due to significant bradycardia, he was initially diagnosed with pacemaker malfunction. Subsequent interrogation of the device revealed a normally functioning biventricular pacemaker. After treating his underlying medical problems, the electrocardiogram returned to baseline.
Embedding the literacy strategy: snapshots of change
Authors: Fisher Ros
Published: October 2004

This paper considers the government's initiative to change the teaching of literacy in primary schools in England. It draws on evidence from a one‐year ESRC‐funded project that observed teaching in the first year of the NLS and a two‐year follow‐up study that revisited and re‐interviewed several of the teachers from the original study. It proposes that, although substantial changes have been made to the organisation and procedures of literacy teaching, deeper pedagogical change is less obvious in some classrooms. It further argues that for teachers to have the freedom to develop their pedagogy, the climate of coercion and outcome‐led education must change.
Prenatal nicotine exposure increases the strength of GABAA receptor‐mediated inhibition of respiratory rhythm in neonatal rats
Authors: Luo Zili , Costy‐Bennett Seres , Fregosi Ralph F.
Published: October 2004

Infants born to mothers that smoke while pregnant have a relatively high incidence of central respiratory control abnormalities. Recent studies have shown that prenatal nicotine exposure increases GABA release and the frequency of GABAergic currents, leading to an up‐regulation of GABAA receptors in central neurones. Activation of GABAA receptors inhibits ventilatory activity, with intense activation causing apnoea. These observations lead us to hypothesize that prenatal nicotine exposure alters GABAergic control of respiratory motor pattern in the early neonatal period. Osmotic minipumps were implanted in pregnant Sprague‐Dawley rats on the fifth day of gestation, and filled with nicotine (6 mg kg−1 day−1, 2.5 μl h−1) or physiological saline (2.5 μl h−1). Brainstem–spinal cord preparations from 1‐ to 3‐day‐old neonates were studied under in vitro conditions. Electrical activity was recorded from the fourth cervical ventral root (C4 VR), which contains the axons of phrenic motoneurones. Bath application of GABAA receptor agonists muscimol (250 μm) or pentobarbital sodium (60 μm) to the brainstem led to consistent, reversible and significant reductions in C4 VR burst frequency. In saline‐exposed animals, frequency (bursts min−1) fell from 6.8 ± 0.4 to a nadir of 2.8 ± 0.5 with muscimol, and from 6.5 ± 0.3 to a nadir of 2.9 ± 0.3 for pentobarbital; in nicotine‐exposed animals, frequency fell from 6.3 ± 0.4 to 1.0 ± 0.4 with muscimol and from 6.4 ± 0.2 to 1.7 ± 0.4 with pentobarbital (P < 0.05 in all cases). The decrease in C4 VR frequency was significantly greater in nicotine‐exposed compared to saline‐exposed preparations with both muscimol and pentobarbital (P < 0.001 for both). There were no changes in the amplitude of C4 VR bursts under any condition. The GABAA receptor antagonist bicuculline methiodide (8 μm) did not change C4 VR frequency or amplitude in either group, although it was effective in reversing the effects of muscimol. These experiments demonstrate that prenatal nicotine exposure alters the GABAergic regulation of respiratory rhythm in a reduced preparation. The results may lead to a better understanding of the perturbed breathing pattern observed in neonates that are exposed to nicotine in utero.
Increased corticospinal excitability after 5 Hz rTMS over the human supplementary motor area
Authors: Matsunaga Kaoru , Maruyama Atsuo , Fujiwara Toshiyuki , Nakanishi Ryoji , Tsuji Sadatoshi , Rothwell John C.
Published: October 2004

Transcranial magnetic stimulation (TMS) can produce effects not only at the site of stimulation but also at distant sites to which it projects. Here we examined the connection between supplementary motor area (SMA) and the hand area of the primary motor cortex (M1Hand) by testing whether prolonged repetitive TMS (rTMS) over the SMA can produce changes in excitability of the M1Hand after the end of the stimulus train. We evaluated motor‐evoked potentials (MEPs) and the cortical silent period (CSP) evoked by a single‐pulse TMS, short‐interval intracortical inhibition (SICI) and intracortical facilitation (ICF) produced by a paired‐pulse TMS, and forearm flexor H reflexes before and after 750 pulses of 5 Hz rTMS over SMA at an intensity of 110% active motor threshold (AMT) for the first dorsal interosseous (FDI) muscle. The amplitude of MEPs recorded from the right FDI muscle at rest as well as during voluntary contraction increased for at least 10 min after the end of rTMS, although the duration of the CSP, SICI and ICF did not change. There was no effect on H reflexes in the flexor carpi radialis muscle, even though the amplitude of the MEP obtained from the same muscle increased after rTMS. The effects on MEPs depended on the intensity of rTMS and were spatially specific to the SMA proper. We suggest that 5 Hz rTMS over SMA can induce a short‐lasting facilitation in excitability of the M1Hand compatible with the anatomical connections between SMA and the M1Hand.
Pancreatic two P domain K+ channels TALK‐1 and TALK‐2 are activated by nitric oxide and reactive oxygen species
Authors: Duprat F. , Girard C. , Jarretou G. , Lazdunski M.
Published: October 2004

This study firstly shows with in situ hybridization on human pancreas that TALK‐1 and TALK‐2, two members of the 2P domain potassium channel (K2P) family, are highly and specifically expressed in the exocrine pancreas and absent in Langherans islets. On the contrary, expression of TASK‐2 in mouse pancreas is found both in the exocrine pancreas and in the Langherans islets. This study also shows that TALK‐1 and TALK‐2 channels, expressed in Xenopus oocytes, are strongly and specifically activated by nitric oxide (obtained with a mixture of sodium nitroprussate (SNP) and dithiothreitol (DTT)), superoxide anion (obtained with xanthine and xanthine oxidase) and singlet oxygen (obtained upon photoactivation of rose bengal, and with chloramine T). Other nitric oxide and reactive oxygen species (NOS and ROS) donors, as well as reducing conditions were found to be ineffective on TALK‐1, TALK‐2 and TASK‐2 (sin‐1, angeli's salt, SNP alone, tBHP, H2O2, and DTT). These results suggest that, in the exocrine pancreas, specific members of the NOS and ROS families could act as endogenous modulators of TALK channels with a role in normal secretion as well as in disease states such as acute pancreatitis and apoptosis.
Raised dietary n‐6 polyunsaturated fatty acid intake increases 2‐series prostaglandin production during labour in the ewe
Authors: Elmes M. , Green L. R. , Poore K. , Newman J. , Burrage D. , Abayasekara D. R. E. , Cheng Z. , Hanson M. A. , Wathes D. C.
Published: October 2004

Preterm labour is the major cause of perinatal morbidity and mortality in humans. The incidence is around 10% and the causes are often unknown. Consumption of dietary n‐6 polyunsaturated fatty acids (PUFAs) in western societies is increasing. These are metabolized to arachidonic acid, the precursor for 2‐series prostaglandins (PGs), major signalling molecules during labour. This study investigated the effect of dietary supplementation with linoleic acid (LA, 18: 2, n‐6) on parturition. Ewes were fed a control or LA‐supplemented diet from 100 days gestation. Labour was induced using a standardized glucocorticoid challenge (dexamethasone, Dex) to the fetus, starting on day 139. Electromyographic (EMG) activity and fetal and maternal circulating PG concentrations were monitored. One third of LA‐fed ewes delivered early (pre‐Dex) although basal uterine EMG activity preceding Dex was higher in control ewes (P < 0.05). A steep increase in EMG activity occurred 18–38 h after the start of Dex infusion. Twice basal EMG activity (defined as established labour) occurred on average 7 h earlier in the LA‐supplemented ewes (P < 0.05). The basal concentrations of maternal and fetal PGFM and fetal PGE2 were approximately doubled in LA‐supplemented ewes before the start of Dex infusion (P < 0.01). The rise in fetal PGE2 and maternal oestradiol concentrations post‐Dex occurred earlier in the LA‐supplemented ewes. All PG measurements remained significantly higher in the LA‐supplemented ewes during labour onset. This study suggests that consumption of a high LA diet in late pregnancy can enhance placental PG production and may thus increase the risk of preterm labour.
Low threshold calcium currents in rat cerebellar Purkinje cell dendritic spines are mediated by T‐type calcium channels
Authors: Isope Philippe , Murphy Timothy H.
Published: October 2004

The functional role of low voltage activated (LVA) calcium channels in the cerebellar Purkinje cell dendritic tree is not completely understood. Since the localization of these channels will influence their possible roles in dendritic integration and induction of plasticity, we set out to characterize the LVA calcium current in Purkinje cell dendrites in acute cerebellar slices of young rats. Using a combination of electrophysiological recordings and two‐photon laser scanning microscopy, we show that LVA calcium current recorded at the soma can be correlated with voltage‐dependent calcium transients in Purkinje cell dendritic spines. Blocking sodium and potassium conductances allowed us to isolate and characterize a fast inactivating inward current activated positive to −55 mV. Activation and steady‐state inactivation kinetics, voltage‐dependent deactivation kinetics, and pharmacological experiments (using ω‐agatoxin‐IVA, mibefradil and nickel) show that this current is carried by T‐type calcium channels. Furthermore, the LVA calcium transient observed in the dendritic spines of the Purkinje cell is well correlated with the current recorded at the soma, suggesting that T‐type calcium channels are the main component of the LVA calcium input in spines. The fast rising phase of the calcium transient in spines and the absence of delay between the onset in the spine and the parent dendrite show that T‐type calcium channels are present both in spines and dendrites of the Purkinje cell.
The influence of normal human ageing on automatic movements
Authors: Wu Tao , Hallett Mark
Published: October 2004

There is evidence that aged normal subjects have more difficulty in achieving automaticity than young subjects. The underlying central neural mechanism for this phenomenon is unclear. In the present study, functional magnetic resonance imaging (fMRI) was used to investigate the effect of normal ageing on automaticity. Aged healthy subjects were asked to practice self‐initiated, self‐paced, memorized sequential finger movements with different complexity until they could perform the tasks automatically. Automaticity was evaluated by having subjects perform a secondary task simultaneously with the sequential movements. Although it took more time, most aged subjects eventually performed the tasks automatically at the same level as the young subjects. Functional MRI results showed that, for both groups, sequential movements activated similar brain regions before and after automaticity was achieved. No additional activity was observed in the automatic condition. While performing automatic movements, aged subjects had greater activity in the bilateral anterior lobe of cerebellum, premotor area, parietal cortex, left prefrontal cortex, anterior cingulate, caudate nucleus and thalamus, and recruited more areas, including the pre‐supplementary motor area and the bilateral posterior lobe of cerebellum, compared to young subjects. These results indicate that most healthy aged subjects can perform some complex motor tasks automatically. However, aged subjects appear to require more brain activity to perform automatically at the same level as young subjects. This appears to be the main reason why aged subjects have more difficulty in achieving automaticity.
Relations between substrate affinities and charge equilibration rates in the rat GABA cotransporter GAT1
Authors: Soragna Andrea , Bossi Elena , Giovannardi Stefano , Pisani Rossana , Peres Antonio
Published: October 2004

The relations between apparent affinity for substrates and operating rates have been investigated by two‐electrode voltage clamp in the GABA transporter rGAT1 expressed in Xenopus oocytes. We have measured the transport current induced by the presence of GABA, as well as the charge equilibration rate in the absence of the neurotransmitter, in various experimental conditions known to affect the transporter characteristics. The apparent affinities for GABA and for Na+ were also determined in the same conditions. Two pharmacological actions and three mutated isoforms have been examined. In all cases significant correlations were found between the charge equilibration rates and apparent affinities for both substrates. In particular in the transport process, the apparent affinity for GABA appears to be inversely related to the sum of the unidirectional charge equilibration rates (α+β), while the Na+ apparent affinity is directly related to their ratio (β/α). Together these observations suggest a kinetic basis for GABA affinity with higher turnover rates resulting in lower affinity, and indicate that an efficient uptake requires a compromise between these two parameters.
Kainate receptors and rhythmic activity in neuronal networks: hippocampal gamma oscillations as a tool
Authors: Fisahn André
Published: October 2004

Rhythmic electrical activity is ubiquitous in neuronal networks of the brain and is implicated in a multitude of different processes. A prominent example in the healthy brain is electrical oscillations in the gamma‐frequency band (20–80 Hz) in hippocampal and neocortical networks, which play an important role in learning, memory and cognition. An example in the pathological brain is electrographic seizures observed in certain types of epilepsy. Interestingly the activation of kainate receptors (KARs) plays an important role in synaptic physiology and plasticity, and can generate both gamma oscillations and electrographic seizures. Electrophysiological recordings of extracellular gamma oscillations and intracellular currents in a hippocampal slice combined with computer modelling can shed light on the expression loci of KAR subunits on single neurones and the distinct roles subunits play in rhythmic activity in the healthy and the pathologicalal brain. Using this approach in wild‐type (WT) and KAR knockout mice it has been shown that KAR subunits GluR5 and GluR6 have similar functions during gamma oscillations and epileptiform bursts and that small changes in the overall activity in the hippocampal area CA3 can tilt the balance between excitation and inhibition and cause the neuronal network to switch from gamma oscillations to epileptiform bursts.
Detection of Methane in the Atmosphere of Mars
Authors: Formisano Vittorio , Atreya Sushil , Encrenaz Thérèse , Ignatiev Nikolai , Giuranna Marco
Published: October 2004

We report a detection of methane in the martian atmosphere by the Planetary Fourier Spectrometer onboard the Mars Express spacecraft. The global average methane mixing ratio is found to be 10 ± 5 parts per billion by volume (ppbv). However, the mixing ratio varies between 0 and 30 ppbv over the planet. The source of methane could be either biogenic or nonbiogenic, including past or present subsurface microorganisms, hydrothermal activity, or cometary impacts.
Hepcidin Regulates Cellular Iron Efflux by Binding to Ferroportin and Inducing Its Internalization
Authors: Nemeth Elizabeta , Tuttle Marie S. , Powelson Julie , Vaughn Michael B. , Donovan Adriana , Ward Diane McVey , Ganz Tomas , Kaplan Jerry
Published: October 2004

Hepcidin is a peptide hormone secreted by the liver in response to iron loading and inflammation. Decreased hepcidin leads to tissue iron overload, whereas hepcidin overproduction leads to hypoferremia and the anemia of inflammation. Ferroportin is an iron exporter present on the surface of absorptive enterocytes, macrophages, hepatocytes, and placental cells. Here we report that hepcidin bound to ferroportin in tissue culture cells. After binding, ferroportin was internalized and degraded, leading to decreased export of cellular iron. The posttranslational regulation of ferroportin by hepcidin may thus complete a homeostatic loop: Iron regulates the secretion of hepcidin, which in turn controls the concentration of ferroportin on the cell surface.
Nuclear Pore Complex Structure and Dynamics Revealed by Cryoelectron Tomography
Authors: Beck Martin , Förster Friedrich , Ecke Mary , Plitzko Jürgen M. , Melchior Frauke , Gerisch Günther , Baumeister Wolfgang , Medalia Ohad
Published: October 2004

Nuclear pore complexes (NPCs) are gateways for nucleocytoplasmic exchange. To analyze their structure in a close-to-life state, we studied transport-active, intact nuclei from
Dictyostelium discoideum
by means of cryoelectron tomography. Subvolumes of the tomograms containing individual NPCs were extracted in silico and subjected to three-dimensional classification and averaging, whereby distinct structural states were observed. The central plug/transporter (CP/T) was variable in volume and could occupy different positions along the nucleocytoplasmic axis, which supports the notion that it essentially represents cargo in transit. Changes in the position of the CP/T were accompanied by structural rearrangements in the NPC scaffold.
ERBIUM-DOPED FIBER AMPLIFIERS FOR MULTIWAVELENGTH LIGHTWAVE NETWORKS: IMPACT OF THE NON-FLAT GAIN SPECTRUM
Authors: GOLDSTEIN EVAN L. , ESKILDSEN LARS
Published: October 2004

The effort to build amplified multiwavelength lightwave networks that are large and reconfigurable has raised a host of hard technological challenges, ranging from device-level difficulties to transmission engineering to network-management concerns. Not least of these are the challenges posed by the spectral gain nonuniformities, and the associated multiwavelength noise performance, of such a network's cascaded optical amplifiers. This paper catalogs the research challenges posed by multiwavelength amplification in networks, summarizes the theory underlying them, and describes approaches that are emerging to lessen their ill effects.
RELIABILITY OF HIGH POWER PUMP LASERS FOR ERBIUM-DOPED FIBER AMPLIFIERS
Authors: FUKUDA MITSUO
Published: October 2004

The degradation behavior and the reliability of 980 nm lasers and 1480 nm lasers are reviewed and discussed. In addition, packaging problems for the high power lasers are also discussed from the application viewpoint. For 980 nm lasers the reliability in laser chip is limited mainly by the instability of an interface between the laser material (facet) and the anti-reflecting coating film, and for most 1480 nm lasers the reliability of the laser chip is determined mainly by the instability of a buried heterointerface. These reliability problems have been solved, however, by examining the material properties and improving device fabrication technology. The main packaging problem is a packaging-induced failure (PIF) causing sudden failure in 980 nm lasers sealed in dry N2 or Ar, but packaging problems have also been suppressed or eliminated. The device technology and packaging technology needed to make high power pump laser modules have been established, and erbium-doped fiber amplifiers pumped by these lasers are indispensable components of many optical transmission systems.
GAIN DYNAMICS AND ASSOCIATED NONLINEARITIES IN SEMICONDUCTOR OPTICAL AMPLIFIERS
Authors: WIESENFELD J. M.
Published: October 2004

A rich variety of dynamical processes underlie the operation of active semiconductor light-emitting devices, such as semiconductor optical amplifiers. These processes include interband and intraband carrier dynamics. Interband processes comprise spontaneous recombination, both radiative and Auger, stimulated radiative recombination, and carrier transport. Intraband processes comprise carrier heating and cooling and spectral hole-burning, among others. The dynamical processes affect both the gain and refractive index of the semiconductor optical amplifier. In this article, these dynamic processes and their physical origins are reviewed. Under conditions of large, time-varying changes in carrier density or intraband carrier distribution, nonlinear gain and refraction becomes significant. For applications requiring linear amplification, such nonlinearities are deleterious. However, for many applications such nonlinearities can be the basis for useful device functions. In particular, the nonlinearities of cross-gain modulation, cross-phase modulation, and four-wave mixing in semiconductor optical amplifiers have been applied for the functions of wavelength conversion, optical time-demultiplexing, clock recovery, and trans-multiplexing. Such nonlinear devices based on semiconductor optical amplifiers and their effects on propagating optical signals are also reviewed.
INTRODUCTION TO LOW-POWER VLSI DESIGN
Authors: YEAP GARY , WILD ANDREAS
Published: October 2004

The paper is a survey of the current status of research and practices in various disciplines of low-power VLSI developments. After briefly discussing the rationale of the contemporary focus on low-power design, it presents the metrics and techniques used to assess the merits of the various solutions proposed for improved energy efficiency. The requirements to be fulfilled by process technologies and device structures are reviewed as well as several promising circuit design styles and ad hoc design techniques. The impact of the design automation tools is analyzed with a special emphasis on physical design and logic synthesis. A review of various architectural trade-offs, including power management, parallelism and pipelining, synchronous versus asynchronous architectures and dataflow transformations are covered, followed by a brief discussion of the impact of the system definition, software and algorithms to the overall power efficiency. Emerging semiconductor technologies and device structures are discussed and the paper is concluded with the trends and research topics for the future.
A NEW CMOS DRIVER MODEL FOR TRANSIENT ANALYSIS AND POWER DISSIPATION ANALYSIS
Authors: LIAO HAIFANG , DAI WAYNE WEI-MING , WANG RUI
Published: October 2004

While most transient analysis techniques of interconnect networks ignore the nonlinearity of the driving gates, most CMOS driver models do not take into account the distributed loads. In this paper, we propose a new CMOS driver model which can handle distributed-lumped loads for transient analysis and power dissipation analysis. The output current of the CMOS driver is represented by a linear-quadratic-exponential piecewise model, taking into account the slope of the input signal, nonlinear effects of the driver and interconnect effects of the load. The CMOS transient leakage (short-circuit) current, thus short-circuit power dissipation, can be accurately evaluated. The model provides accuracy comparable to that of SPICE3e2 with one or two orders of magnitude less computing time.
FLOORPLAN DESIGN WITH LOW POWER CONSIDERATIONS
Authors: CHAO KAI-YUAN , WONG D. F.
Published: October 2004

In this paper, a floorplanner for low power design is presented. Our objective is to optimize total power consumption and area during the selection and placement of various implementations for circuit modules. Furthermore, the proposed method considers performance requirements, power line noises, and distribution of power consumption in order to generate lower and evenly distributed power dissipation over the resulting circuit floorplan with a specified performance. For a set of benchmark circuits we tested, on the average, our floorplanner can achieve decreases of total power consumption, wire-length, and power/ground network size by 18.3%, 4.6%, and 24%, respectively, at the cost of an area increase of 8.8% when compared with an existing area/wire-length driven floorplanner.
RETIMING SEQUENTIAL CIRCUITS FOR LOW POWER
Authors: MONTEIRO JOSÉ , DEVADAS SRINIVAS , GHOSH ABHIJIT
Published: October 2004

Switching activity is a primary cause of power dissipation in combinational and sequential circuits. In this paper, we present a retiming method that targets the power dissipation of a sequential circuit by reducing the switching activity of nodes driving large capacitive loads. We explore the implications of the observation that the switching activity at flip-flop outputs in a synchronous sequential circuit can be significantly less than the activity at the flip-flop inputs. The method automatically determines positions of flip-flops in the circuit so as to heuristically minimize weighted switching activities summed over all the gates and flip-flops in the circuit. We extend this method to minimize power dissipation with a specified clock period. For this work we need to obtain efficiently an estimation of the switching activity of every node in the circuit. We give an exact method of estimating power in pipelined sequential circuits that accurately models the correlation between the vectors applied to the combinational logic of the circuit. This method is significantly more efficient than methods based on solving Chapman–Kolmogorov equations. Experimental results are presented on a variety of circuits.
OPTICAL SOLITON COMMUNICATION RESEARCH IN CHINA
Authors: WANG HONG , YE PEIDA
Published: October 2004

The optical soliton communication research in China, which began in 1984, is reviewed briefly in this paper. The main theoretical works include: optical soliton transmission characteristics, optimal design of optical soliton communication system and theories related to the key components such as soliton sources, EDFA, etc. An experimental system with 2.5 Gb/s, 21 km has been developed. Possible developments in the near future is viewed.
ANALYSIS AND EXPERIMENT OF MULTICHANNEL WDM + EDFA OPTICAL FIBER TRANSMISSION SYSTEMS
Authors: XU ANSHI , WU DEMING , XIANG QIANGSHENG , ZHANG KAN , WANG CHU , XIE LINZHEN
Published: October 2004

A 151 km "WDM + EDFA" optical fiber transmission system with 8 channels and 2 EDFAs has been built for the first time in China. Some formulas are given to estimate the effect of optical signal power and ASE noise on BER, the power penalty caused by the Stimulated Raman Scattering (SRS) and the crosstalk due to the grating demultiplexer in optical amplified WDM systems with EDFAs. The calculation results are well agreed with experimental data.

In addition, an 8-channel, optically amplified WDM system with regenerated transmission distance of 1208 km, an 8-channel, 240 km optically amplified WDM system and a 12-channel, 240 km optically amplified WDM system have been developed successively.
THE CALCULATION OF POWER PENALTY IN "WDM + EDFA" SYSTEM DUE TO STIMULATED RAMAN SCATTERING
Authors: XIANG QIANGSHENG , XU ANSHI , WU DEMING , XIE LINZHEN
Published: October 2004

A general expression is derived to calculate the power penalty due to Stimulated Raman Scattering (SRS) in a WDM system with EDFAs. It is concluded that the damage to the "WDM + EDFA" system caused by SRS depends greatly on the disposal of the EDFAs, and an easy way has been provided to minimize the power penalty. Finally, expressions are given to estimate the transmission distance and the number of EDFAs limited by SRS in the "WDM + EDFA" system.
AN INVESTIGATION OF MULTI-FUNCTIONAL SEMICONDUCTOR BISTABLE LASER
Authors: WANG QIMING , WU RONGHAN , LIN SHIMING , LI JIANMENG , XIONG FEIKE , ZHANG QUANSHENG
Published: October 2004

The co-cavity two-section (CCTS) bistable semiconductor laser with DH and MQW structures has been investigated experimentally and theoretically in this laboratory. Many attractive functions, such as optical bistable switching, optical memory effect, high stability of single longitudinal mode emission spectrum in steady on state, high gain optical amplification, mode conversion effect on injecting signal light, long delay and abnormal relaxation oscillation, ultrafast light pulse generation are investigated in the device. As a high speed, single wavelength, novel laser light source, a monolithic MQW CCTS bistable laser with MQW EA modulator has been fabricated.
A PRACTICAL ELECTRO-OPTIC SAMPLER FOR CHARACTERIZATION INTERNAL TO GaAs ICs
Authors: YI MAOBIN , SUN WEI , TIAN XIAOJIAN , JIA GANG , LIU SHIYONG
Published: October 2004

This paper describes a practical electro-optic sampler of the measuring-microscope mode for noninvasive measurements of voltage waveforms at points internal to a GaAs integrated circuit. A 360° linear sweep phase shifter is used to provide the scanning delay of the sampling point in time, and was typically demonstrated in measuring the dynamic frequency divider circuit. In addition to the characterization internal to GaAs ICs, the overlap of the electrical signal field in an integrated circuit and the interference effect on the signal voltage calibration are also investigated.
LOW COST, LOW POWER DIGITAL OPTICAL RECEIVER MODULE FOR 50 Mb/s PASSIVE OPTICAL NETWORK
Authors: OTA YUSUKE , SWARTZ ROBERT G. , SCHAFER JOHN S. , BANU MIHAI M. , DUNLOP ALFRED E. , FISCHER WILHELM C. , GABARA THADDEUS J.
Published: October 2004

A low cost digital optical receiver module for passive optical networks was developed. In order to reduce the cost of the receiver module, ICs are packaged in low cost plastic packages and the receiver module is fabricated using conventional surface mount technology. The receiver module is capable of receiving burst and packet digital optical signals, and recovered data and recovered clock in CMOS logic level are available. The receiver module contains a connectorized InGaAs PIN photodiode, a burst/packet mode-compatible preamplifier IC in a 32-lead TQFP plastic package, a comparator IC in an 8-lead SOIC plastic package, a clock recovery IC in a 32-lead TQFP plastic package and other active and passive components. These components are mounted on a four-layer printed wiring board. The intrinsic minimum receivable optical signal power is around -42 dBm/Ave and the dynamic range is over 26 dB for BER 1 × 10-8 at a bit rate of up to 60 Mb/s. The total power consumption of this module is less than 200 mW.
THE DATA STRUCTURE ACCELERATOR ARCHITECTURE
Authors: ZIPPEL RICHARD
Published: October 2004

We present a heterogeneous architecture that contains a fine grained, massively parallel SIMD component called the data structure accelerator and demonstrate its use in a number of problems in computational geometry including polygon filling and convex hull. The data structure accelerator is extremely dense and highly scalable. Systems of 106 processing elements can be embedded in workstations and personal computers, without dramatically changing their cost. These components are intended for use in tandem with conventional single sequence machines and with small scale, shared memory multiprocessors. A language for programming these heterogeneous systems is presented that smoothly incorporates the SIMD instructions of the data structure accelerator with conventional single sequence code. We then demonstrate how to construct a number of higher level primitives such as maximum and minimum, and apply these tools to problems in logic and computational geometry. For computational geometry problems, we demonstrate that simple algorithms that take advantage of the parallelism available on a data structure accelerator perform as well or better than the far more complex algorithms which are needed for comparable efficiency on single sequence computers.
NONLINEAR OPTICS OF POLYMERS: FUNDAMENTALS AND APPLICATIONS
Authors: BLOEMBERGEN N.
Published: October 2004

A broad review of nonlinear optical properties of polymeric materials and devices is presented.
GENERATION OF MID-INFRARED RADIATION BY IMPACT IONIZATION OF DEEP-CENTERS IN SEMICONDUCTOR STRUCTURES
Authors: SCAMARCIO G. , CAPASSO F. , HUTCHINSON A.L. , TANBUN-EK T. , SIVCO D.L. , CHO A.Y.
Published: October 2004

Narrow-band mid-infrared electroluminescence associated with internal transitions of metal impurities embedded in semiconductors following the impact ionization of the latter is reported. We have demonstrated this phenomenon for Fe2+ deep acceptors in InP. At 10 K the spectrum is dominated by a set of sharp lines at 3.5 µm, corresponding to the symmetry allowed (5T2→5E) d-shell transitions of Fe2+. Optical power up to ≈40 nW has been measured.
LOCALIZATION EFFECTS IN SEMICONDUCTOR SUPERLATTICES
Authors: LEE S.J. , KHURGIN J.B.
Published: October 2004

We investigated two novel effects utilizing localization properties of semiconductor super-lattices. First, a phenomenon which consists of optically induced effective mass change due to carrier localization in semiconductor superlattices is investigated. It is shown that an optical field can achieve conductivity changes in a manner similar to a dc electric field. A possible application as a nonabsorbing differential optical detector/switch is considered. Second, radiative recombination of the excitonic states in semiconductor superlattices with an applied electric field is studied theoretically. It is shown that when the electron-hole Coulomb interaction energy exceeds the miniband width, a coherent excitonic state is created whose oscillator strength surpasses the oscillator strength of a single quantum well by orders of magnitude. It is also demonstrated that a small external field can split the coherent state into isolated well states and thus severely deplete the oscillator strength of the exciton. This opens the possibility of modulating and switching of superradiance in semiconductor devices.
EXCITONIC SELF-INDUCED TRANSPARENCY IN SEMICONDUCTORS
Authors: TALANINA I.B.
Published: October 2004

The form invariant coherent pulse propagation in semiconductors excited at 1s-exciton resonance is studied analytically using the reduced semiconductor Maxwell-Bloch equations. The sech-shaped pulse solution for excitonic self-induced transparency (SIT) is presented, showing significant difference in comparison with the well known SIT solution for non-interacting two-level systems. In contrast to 2π pulses in atomic systems, the phenomenon of SIT of interacting excitons in semiconductors occurs for the pulses of area 1.07π. Possible applications of the SIT solitons in semiconductor all-optical switching devices are discussed.
FEMTOSECOND HYPER-RAYLEIGH SCATTERING STUDY OF SPATIAL ORIENTATIONAL CORRELATIONS BETWEEN CHROMOPHORES
Authors: CLAYS K. , WU M. , PERSOONS A.
Published: October 2004

Since the introduction of Hyper-Rayleigh scattering (HRS) as a measurement technique for the first hyperpolarizability of molecules in solution,1 the importance of fluctuations was realized.2 For isotropic solutions, a combination of the spatial and temporal orientational fluctuations causes the instantaneous and local deviation from macroscopic centrosymmetry, necessary to observe a second-order signal. The fluctuations in the spatial orientational distribution function of nonlinear optical chromophores cause an HRS signal that fluctuates as a function of position in solid samples. The correlation length, characterizing the decay of the autocorrelation function of this fluctuating signal, indicates the degree of spatial correlation between these chromophores. The development of femtosecond HRS was instrumental for the study of orientational correlations.3
NEW NLO POLYMERS FOR SECOND AND THIRD HARMONIC GENERATIONS
Authors: ABE H. , RIKUKAWA M. , OGATA N.
Published: October 2004

Poly(L-glutamate)s (PLG) having NLO active chromophore in side chains were synthesized by an ester exchange reaction of methyl ester of PLG with 4-(3-hydroxypropoxy)-4’-nitrostilbene or other alcohols containing the nitrostilbene moiety, and the NLO properties of these polymers were investigated in terms of second harmonic generation (SHG). These polymers exhibited rather stable poled structures after electric poling, possibly owing to the helical structures of PLG. Aromatic polymers such as poly(p-phenylene) are thermally stable with high glass transition temperatures. Poly(p-phenylene) derivatives having various donor or acceptor groups were used to measure NLO properties in terms of SHG and third harmonic generations (THG). They showed high SH coefficients with less relaxation behaviors of the poled structures.
QUANTUM DOTS OF LIGHT
Authors: KELLER O.
Published: October 2004

Basic ingredients of a microscopic theory describing the degenerate four-wave mixing of the outgoing field from a mesoscopic source particle were established. Starting from many-body theory and selfenergy quantum electrodynamics it is argued that the best spatial confinement one might hope to obtain of the source field is given by the extension of the transverse part of the current density distribution induced in the mesoscopic particle. Taking into account the phaseconjugation of evanescent components of the source field, the existence of so-called quantum dots of light having a subwavelength extension is predicted. Using the outgoing field from the tip of an optical near-field microscope in combination with a phaseconjugating mirror exhibiting a sufficiently long memory time light dots can be made experimentally. A new nonlocal nonlinear response tensor enabling one to study the four-wave mixing process of the local field itself is presented.
QUADRATIC NONLINEAR SURFACE WAVES
Authors: TRAN H.T.
Published: October 2004

Nonlinear surface waves at an interface between a linear medium and another medium with quadratic nonlinearity are possible due to the phenomenon of nonlinearity-induced phase matching. The waves are numerically calculated, along with their dispersion, stability, and comparison with their cubic counterparts. An extension to guided waves is also discussed.
MIRRORLESS OPTICAL PARAMETRIC OSCILLATORS
Authors: DING YUJIE J. , KHURGIN JACOB B.
Published: October 2004

We have considered two novel configurations for optical parametric oscillators (OPO’s): transversely-pumped counter-propagating and nondegenerate backward OPO’s due to the distributed feedback provided through the opposite propagation directions of the signal and idler. In both configurations, by changing the incident angle of the pump beam, one can tune the output frequency in a large range. The threshold pump powers for the oscillation can be as low as ~10 W for the transversely-pumped counter-propagating OPO’s and 44 W for the nondegenerate backward OPO’s. The quasi-phase matching is achieved by spatially modulating second-order susceptibility along the growth direction based on semiconductor alternating thin layers or asymmetric quantum-well domain structures or by electric-field poling in conventional second-order nonlinear materials. The nondegenerate backward OPO’s offer the most efficient conversion among all the configurations for the OPO’s having the same threshold pump power. The transversely-pumped counter-propagating OPO’s have the optimal pump power.
IMAGING THROUGH SCATTERING MEDIA BY PARAMETRIC IMAGE AMPLIFICATION
Authors: DEVAUX F. , LANTZ E. , MAILLOTTE H.
Published: October 2004

Parametric image amplification is proposed as a new solution for detecting objects hidden by scattering media. An image of a resolution chart has been obtained through a milk cell 18 scattering mean free paths thick. The ballistic light is amplified with a mean gain of 40 dB and the resolution on the object is about 20 μm.
Z-SCANS WITH NEAR-GAUSSIAN LASER BEAMS
Authors: CHAPPLE P.B. , WILSON P.J.
Published: October 2004

Laboratory measurements of optical nonlinearities can be significantly affected by imperfections in the laser beam profiles. Here the effects of beam profile on Z-scan measurements are calculated for a large number of near-Gaussian beams. These effects are modeled for Z-scans of thin media, for both refractive and absorptive nonlinearities. The difference ∆T between the maximum and minimum values of the normalized transmittance generally increases with the beam quality factor M2 (as the beam quality declines). for a given beam power and waist size. The scatter in ∆T values also increases with M2.
THE SYNTHESIS, CHARACTERIZATION, AND PHOTOCHEMICAL CROSSLINKING OF AN NLO EPOXY POLYMER
Authors: GOODSON T. , TAKACS J.M. , WANG C.H. , ZHANG L.
Published: October 2004

A photocrosslinkable second order nonlinear optical (NLO) epoxy polymer, Bisphenol A-Nitroaminotolane, containing covalently attached cinnamate side chain substituents (BisA-NAT-CM), was synthesized. After corona poling Second Harmonic Generation (SHG) is used to measure the relaxation of the anisotropy after the electric field is removed. Upon photolysis at 260 nm the cinnamoyl side chains undergo photochemical dimerization to crosslink the NLO polymer. Photobleaching is not a problem under these conditions. The photocrosslinked NLO polymer shows virtually no relaxation over a period of 500 hours at room temperature and good temporal stability at temperatures as high as 110°C.