bluuebunny/crossref_metadata_2025 huggingface dataset:
Debris-Covered Glaciers in the Sierra Nevada, California, and Their Implications for Snowline Reconstructions
Authors: Clark Douglas H. , Clark Malcolm M. , Gillespie Alan R.
Published: October 2002

Ice-walled melt ponds on the surfaces of active valley-floor rock glaciers and Matthes (Little Ice Age) moraines in the southern Sierra Nevada indicate that most of these landforms consist of glacier ice under thin (ca. 1 - 10 m) but continuous covers of rock-fall-generated debris. These debris blankets effectively insulate the underlying ice and greatly reduce rates of ablation relative to that of uncovered ice. Such insulation explains the observations that ice-cored rock glaciers in the Sierra, actually debris-covered glaciers, are apparently less sensitive to climatic warming and commonly advance to lower altitudes than do adjacent bare-ice glaciers. Accumulation-area ratios and toe-to-headwall-altitude ratios used to estimate equilibrium-line altitudes (ELAs) of former glaciers may therefore yield incorrect results for cirque glaciers subject to abundant rockfall. Inadvertent lumping of deposits from former debris-covered and bare-ice glaciers partially explains an apparently anomalous regional ELA gradient reported for the pre-Matthes Recess Peak Neoglacial advance. Distinguishing such deposits may be important to studies that rely on paleo-ELA estimates. Moreover, Matthes and Recess Peak ELA gradients along the crest evidently depend strongly on local orographic effects rather than latitudinal climatic trends, indicating that simple linear projections and regional climatic interpretations of ELA gradients of small glaciers may be unreliable.
A Preliminary Reconstruction of Rainfall in North-Central China since A.D. 1600 from Tree-Ring Density and Width
Authors: Hughes Malcolm K. , Xiangding Wu , Xuemei Shao , Garfin Gregg M.
Published: October 2002

May-June (MJ) and April-July (AJ) precipitation at Huashan in north-central China has been reconstructed for the period A.D. 1600 to 1988 using tree-ring density and width fromPinus armandii. MJ precipitation (based on ring width and maximum latewood density) calibrated and cross-validated against local instrumental data more strongly than AJ precipitation (based only on ring width). A major drought was reconstructed for the mid- and late 1920s, confirmed by local documentary sources. This drought (culminating in 1929) was the most severe of the 389-yr period for MJ and second most severe for AJ, after an event ending in 1683. Neither reconstruction shows much spectral power at frequencies lower than 1 in 10 yr, but both show concentrations of power between 2.1 and 2.7 yr and 3.5 to 9 yr. There are significant correlations between the two reconstructions and a regional dryness/wetness index (DW) based on documentary sources, particularly at high frequencies. These correlations are focused in the 7.6- to 7.3-, 3.8- to 3.6-, and 2.5-yr periods. Using singular spectrum analysis, quasiperiodic behavior with a period close to 7.2 yr was identified in the MJ precipitation reconstruction and in the DW index based on documents.
An Oxygen-Isotope Paleothermometer from Ice in Siberian Permafrost
Authors: Nikolayev Vladimir I. , Mikhalev Dmitry V.
Published: October 2002

There is a clear linear relationship between mean annual (or seasonal) air temperature at the Earth's surface and the mean oxygen isotopic composition of precipitation in polar regions. Whereas this relationship is well preserved in polar ice caps, it may not be in permafrost because freshly deposited snow in permafrost areas is subjected to great deflation and drifting by wind. Moreover, melting and freezing within the snow cover and the active layer can lead to isotopic fractionation. The δ18O of recent ground ice also depends on its geomorphic context and on the lithology (content of organic matter) of ice-containing sediments. Nevertheless, mean cold-season air temperature near the ground surface and δ18O in recent ground ice are highly correlated. Therefore, the δ18O of ground ice (ice cement and segregated ice) in permafrost areas can be used for paleoclimatic reconstructions.
An Exceptionally Thick Middle Pleistocene Tephra Layer from Epirus, Greece
Authors: Pyle David M. , van Andel Tjeerd H. , Paschos Panayiotis , van den Bogaard Paul
Published: October 2002

A newly recognized 2-m-thick trachytic volcanic ash deposit from northwestern Greece is dated at 374,000 ± 7000 yr and correlated with the Middle Pleistocene volcanic activity of central Italy. The deposit represents ash fallout from one of the largest volcanic eruptions in Europe of the past 400,000 yr and should provide an important stratigraphic marker within the poorly dated Middle Pleistocene deposits of Italy and Greece.
Meltwater Discharge to the Skagerrak–Kattegat from the Baltic Ice Lake during the Younger Dryas Interval
Authors: Jiang Hui , Svensson Nils-Olof , Björck Svante
Published: October 2002

Diatom data from the Skagerrak–Kattegat show that large amounts of meltwater were discharged into the Kattegat–Skagerrak from the Baltic Ice Lake during the Younger Dryas interval. Strong meltwater discharge greatly freshened surface-water salinity in the Kattegat and areas along the Swedish west coast and possibly changed the directions of sea-surface salinity gradients from north–south to east–west or northwest–southeast. It resulted in a markedly stratified water column in salinity in the Kattegat, which complicates the environmental interpretation based on different types of microfossils. The meltwater influence on the large area of the Skagerrak during the Younger Dryas was, however, restricted along the Norwegian coast where it flowed into the Norwegian Sea.
Problems and Possible Solutions Concerning Radiocarbon Dating of Surface Marine Sediments, Ross Sea, Antarctica
Authors: Andrews John T. , Domack Eugene W. , Cunningham Wendy L. , Leventer Amy , Licht Kathy J. , Jull A. J. Timothy , DeMaster David J. , Jennings Anne E.
Published: October 2002

Radiocarbon accelerator mass spectrometric (AMS) dates on the acid-insoluble fraction from 38 core tops from the western Ross Sea, Antarctica, are used to address these questions: (1) What are the apparent ages of sediments at or close to the present sediment/water interface? (2) Is there a statistically significant pattern to the spatial distribution of core top ages? and (3) Is there a “correction factor” that can be applied to these age determinations to obtain the best possible Holocene (downcore) chronologies? Ages of core top sediments range from 2000 to 21,000 14C yr B.P. Some “old” core top dates are from piston cores and probably represent the loss of sediment during the coring process, but some core top samples >6000 14C yr B.P. may represent little or no Holocene deposition. Four possible sources of variability in dates ≤6000 14C yr B.P. (n = 28) are associated with (1) different sample preparation methods, (2) different sediment recovery systems, (3) different geographic regions, and (4) within-sample lateral age variability. Statistical analysis on an a posteriori design indicates that geographic area is the major cause of variability; there is a difference in mean surface sediment age of nearly 2000 yr between sites in the western Ross Sea and sites east of Ross Bank in south-central Ross Sea. The systematic variability in surface age between areas may be attributed to: (a) variable sediment accumulation rates (SAR) (surface age is inversely related to SAR), (b) differences in the percentage of reworked (dead) carbon between each area, and/or (c) differences in the CO2 exchange between the ocean and the atmosphere.
The novel endoplasmic reticulum (ER)‐targeted protein HAP induces cell apoptosis by the depletion of the ER Ca2+ stores
Authors: Qu Xiaoling , Qi Yipeng , Lan Ping , Li Qilan
Published: October 2002

HAP, a novel human apoptosis‐inducing protein, was identified to localize exclusively to the endoplasmic reticulum (ER) in our previous work. In the present work, we reported that ectopic overexpression of HAP proteins caused the rapid and sustained elevation of the intracellular cytosolic Ca2+, which originated from the reversible ER Ca2+ stores release and the extracellular Ca2+ influx. The HeLa cells apoptosis induced by HAP proteins was not prevented by establishing the clamped cytosolic Ca2+ condition, or by buffering of the extracellular Ca2+ with EGTA, suggesting that the depletion of ER Ca2+ stores rather than the elevation of cytosolic Ca2+ or the extracellular Ca2+ entry contributed to HAP‐induced HeLa cells apoptosis. Caspase‐3 was also activated in the process of HAP‐triggered apoptotic cell death.
Solvent environment conducive to protein aggregation
Authors: Fernández Ariel , de las Mercedes Boland Maria
Published: October 2002

The effect of solvent structuring induced by molecular crowding is elucidated within a competitive situation involving protein folding and aggregation. Two patterned fragments of amyloidogenic proteins are chosen as study cases and analyzed by molecular dynamics with an implicit treatment of the solvent. The extent of crowding needed to induce aggregation is determined. The results constitute a first step to assess the relevance of in vivo environments in understanding fibrillogenesis. The approach is independently validated by satisfactorily reproducing the results of an all‐atom explicit solvent trajectory.
Response of safflower (Carthamus tinctorius L.) to residual soil N following cotton (Gossypium spp.) in rotation in the San Joaquin Valley of California
Authors: BASSIL E. S. , KAFFKA S. R. , HUTMACHER R. A.
Published: October 2002

Deep-rooted crops used in rotation can improve the overall water and N use efficiencies of cropping systems and help minimize nitrate leaching to groundwater. Safflower (Carthamus tinctorius L.) is a deep-rooted annual crop grown in Mediterranean regions that might be useful for this purpose. Safflower's response to residual soil N measured to 2.7 m in the soil profile was evaluated in 1998 in field plots in the San Joaquin Valley, California, USA that were used previously for cotton over a 9-year period and had been fertilized with nine N rates from 0 to 230 kg N/ha. Residual soil NO3-N measured prior to safflower planting increased with prior cotton fertilization rates. Amounts present to a soil profile depth of 2.7 m varied from 760 to 2600 kg/ha. Safflower seed yield increased with increasing pre-plant residual NO3-N levels, from 1700 kg/ha in the control to 2200 kg/ha, and then declined to 1800 kg/ha at the largest residual N level. Oil per cent, and oil yield were affected by soil N only at the largest residual N level, while oil composition was not affected. Root growth and N uptake at depth increased in plots with larger amounts of residual N compared to those with less. Results suggest that N fertilization applied to safflower could be reduced or even eliminated following crops previously fertilized at economic levels. Residual N should be accounted in growers' management programmes.
Variations of lactoperoxidase activity and thiocyanate content in cows' and goats' milk throughout lactation
Authors: FONTEH FLORENCE A. , GRANDISON ALISTAIR S. , LEWIS MICHAEL J.
Published: October 2002

Lactoperoxidase activity and thiocyanate content were monitored in the milks of seven individual cows and six goats during lactation. Lactoperoxidase activity exhibited a cyclic pattern with alternating peaks and troughs throughout lactation. Extremely large variations were observed between and within animals. For example, lactoperoxidase activity ranged from 0·05–5·60 U/ml for one cow on different sampling days. Variations between cows were also large, ranging from 0·98–5·1 U/ml on a specific sampling day. Mean lactoperoxidase activity in cows ranged from 1·5–2·7 U/ml with an overall mean of 2·3±1·0 U/ml while the thiocyanate concentration ranged from 6·0–10·2 μg/ml with an overall average of 8·5±5·1 μg/ml. Lactoperoxidase activity means for goats ranged from 0·04–0·16 U/ml with a grand mean of 0·1±0·06 U/ml while the thiocyanate content means ranged from 6·6–8·2 μg/ml with a grand mean of 7·0±2·59 μg/ml. There was no correlation between lactoperoxidase activity and thiocyanate content in either cows' (R2 = 0·011) or goats' (R2 = 0·015) milk. These experiments have revealed that lactoperoxidase activity is affected by many factors including the individual animals, species, feed and stage of lactation. Therefore the exogenous supply of thiocyanate and hydrogen peroxide needed to activate the lactoperoxidase system for raw milk preservation will vary in quantity depending on these factors.
Influence of transglutaminase treatment on some physico-chemical properties of milk
Authors: O'SULLIVAN M. M. , KELLY A. L. , FOX P. F.
Published: October 2002

Transglutaminase (TGase) is an enzyme that cross-links many proteins, including milk proteins. In this study, the effects of TGase on some physico-chemical properties of milk were studied. TGase-treated milk was not coagulable by rennet, which was due to failure of the primary (enzymic) stage of rennet action rather than the non-enzymic secondary phase. Dissociation of TGase-treated casein micelles by urea or sodium citrate or removal of colloidal calcium phosphate by acidification and dialysis was reduced, presumably due to the formation of cross-links between the caseins. Casein micelles in TGase-treated milks were also resistant to high pressure treatment and to hydrolysis by plasmin. Results of the present study show that milk proteins are fundamentally modified by the action of TGase, which may have applications in the manufacture of functional proteins for use as novel food ingredients.
Factors influencing the spatial variation in fish and macrocrustacean communities in the surf zone of sandy beaches in Belgium
Authors: Beyst Bregje , Hostens Kris , Mees Jan
Published: October 2002

An inventory of fish and epibenthic macrocrustaceans of the surf zones of sandy beaches along the Belgian coast was constructed. The surf zones were sampled intensively with a 2-m beam trawl in April–May 1996 (12 stations) and 26 species were recorded belonging to caridean shrimps (4), brachyuran crabs (5), cephalopods (1) and fish (16). The brown shrimp Crangon crangon dominated almost all samples (>80%). Total densities exceeded several times 250 ind 100 m−2 and 10 ind 100 m−2 if C. crangon was excluded. An east–west distinction as found in other (epi)benthic studies in deeper waters of the Belgian coast, was not found in the surf zone during this study. Spatial variation was mainly correlated with local characteristics such as turbidity of the water and the morphodynamic features of both the beach and the adjacent subtidal area.
Intraplant habitat and feeding preference of two gastropod herbivores inhabiting the kelp Laminaria hyperborea
Authors: Toth Gunilla B. , Pavia Henrik
Published: October 2002

The habitat and feeding preference of two gastropod mesoherbivore species, Ansates (Helcion) pellucida and Lacuna vincta, inhabiting the kelp Laminaria hyperborea were investigated by studying the distribution, habitat choice and food preference of the herbivores between new and old kelp fronds. Nitrogen content and chemical defence (phlorotannin) level of the kelp fronds were measured in order to determine whether they were correlated with the feeding preference of the herbivores. The habitat choice of Lacuna vincta was correlated with the food preference of this species, while the habitat choice of A. pellucida probably was due to some other factor, e.g. competition or mortality. Ansates pellucida preferred to reside on the old fronds of Laminaria hyperborea, but consumed an equal amount of both tissue types. Lacuna vincta, however, preferred the new Laminaria hyperborea fronds both as habitat and food. There was a large variation in the phlorotannin content among the tissue samples of L. hyperborea. However, there were no overall statistically significant differences in tissue nitrogen or phlorotannin content between the new and the old L. hyperborea fronds.
First record of the lessepsian migrant Leiognathus klunzingeri (Pisces: Leiognathidae) from the Adriatic Sea
Authors: Dulčić J. , Pallaoro A.
Published: October 2002

Lessepsian migrant Leiognathus klunzingeri is reported for the first time from the Adriatic Sea, substantially further north than its usual area of occurrence in the Mediterranean Sea. Morphometric and meristic characteristics of the specimen are provided. The possible explanations of this occurrence are discussed.
Age estimation in crabeater seals (Lobodon carcinophagus)
Authors: Laws R. M. , Baird A. , Bryden M. M.
Published: October 2002

The age of crabeater seals Lobodon carcinophagus was first estimated from the teeth by counting layers in the dentine in transverse sections of the canine teeth. Reliable estimation of age from canine teeth in animals older than c. 10 years is not possible because of root closure at a relatively early age. The present investigation compared various methods of estimating age by examination of tooth sections from a large sample of crabeater seals from Marguerite Bay, Antarctic Peninsula. The most reliable estimations were shown to be obtained by counting layers in the cementum of the third postcanine tooth. Ages of 1233 animals (58% female, 42% male) ranged from 0.5 to 39 years. It is suggested that time‐ and age‐specific historical material is potentially relevant for contemporary growth and life‐history studies as well as for trophic relations or concentrations of pollutants in animal tissues.
Long-Term Results after Silicone Prosthesis Replacement of the Proximal Pole of the Scaphoid Bone in Advanced Scaphoid Nonunion
Authors: HAUSSMANN P.
Published: October 2002

The treatment of scaphoid fracture nonunion with a small proximal fragment with disturbed circulation and radioscaphoid arthrosis is difficult, and the result is often unsatisfactory. For this reason, in 1981 the replacement of the proximal fragment by a silicone lunate prosthesis was recommended for such cases.

From 1980 to 1984, 11 patients (all male, average age 42 [range, 25–59] years) with the conditions described above were treated by silicone prosthesis partial replacement of the scaphoid. In one patient, the prosthesis had to be removed due to dislocation, and in another patient an arthrodesis of the wrist had to be carried out after 5 years due to increasing pain. All nine remaining patients were followed up after an average of 14 (range, 12–16) years, and were clinically and radiologically re-examined and assessed using the evaluation scheme proposed by Martini (1999) .

The overall results were satisfactory. Specifically, the outcome was good in one case, satisfactory in six cases, and poor in two cases. Concerning the individual criteria, the best scores were observed in “subjective overall assessment” and in “work and sports”, whilst the worst were found in “movement” and “X-ray”. For all patients, X-ray examination revealed both postoperative arthrosis and extensive multiple cystoid osteolysis, presumably due to silicone synovitis. Nevertheless, most patients were free of symptoms. None of the patients felt that further treatment was necessary.

Silicone prosthesis partial replacement of the scaphoid leads to long-term reduction in pain and adequate hand function. However, it is not capable of preventing carpal collapse and carpal arthrosis. Furthermore, since in several cases a progressive silicone synovitis developed, the method was rightly abandone d after 1984.
Medium-Term Results of Trapezio-Lunate External Fixation for Scaphoid Fractures
Authors: GÜNAL Ý. , ÖZTUNA V. , ÖZÇELIK A. , KÖSE N. , TURGUT A. , GÖKTÜRK E. , SEBER S.
Published: October 2002

We treated 36 scaphoid fractures in 34 patients with trapezio-lunate external fixation. According to the Herbert and Fisher classification, there were 16 type B1, 14 type B2, four type B3 and two type B4 fractures. Trapezial and lunate pins broke in three patients and these were rated as failures. The remaining 33 fractures were followed-up for 3 years and all had excellent outcomes, without signs of arthritis, avascularity or instability.
Bone Compression Technique for Arthrodesis and Nonunion In the Hand
Authors: WATSON H. K. , WOLLSTEIN R. , O’SULLIVAN K. , WEINZWEIG J. , ABE Y.
Published: October 2002

We present a simple compression technique for treatment of difficult nonunions and joint fusions in the hand. This technique utilizes only K-wires and small vessel loops. The results of 44 consecutive cases were studied retrospectively. Union was achieved in 37/44 cases. The average time to union was 7 weeks and our results were comparable to those of other studies. We found this technique useful, especially in complicated cases.
Osteoid Osteoma of the Hand and Wrist
Authors: MARCUZZI A. , ACCIARO A. LETI , LANDI A.
Published: October 2002

Eighteen cases of osteoid osteoma of the hand and wrist were treated between 1985 and 1999. The diagnosis was confirmed pre-operatively with X-rays, bone scintigraphy, CT, and MRI, and all the diagnoses were later confirmed by histological examination. The authors highlight the difficulties in the diagnosis of the osteoid osteoma of the hand and wrist. An accurate clinical history and a high index of suspicion are required. Three phase bones scans are highly sensitive for osteoid osteoma and should be used in conjunction with CT examination to facilitate diagnosis and pre-operative planning. All the patients were treated surgically, by removal of the tumour, with complete resolution of all symptoms.
Photodissociation of alkyl and aryl iodides and effect of fluorination: Analysis of proposed mechanisms and vertical excitations by spin–orbit ab initio study
Authors: Ajitha D. , Fedorov D. G. , Finley J. P. , Hirao K.
Published: October 2002

An ab initio study of the vertical electronic excitations in CX3I, C6X5H, and C6X5I (X=H and F) is presented. All-electron basis sets are used and the relativistic effects are accounted for with the relativistic elimination of small components scheme. The structures are optimized with the complete active space self-consistent field approach and the excitation energies are computed with the spin–orbit multiconfiguration quasidegenerate perturbation theory. The n–σ* transitions of CX3I, low-lying π–π* transitions of C6X5H, and low-lying n–σ*, π–π*, and π–σ* transitions of C6X5I are elucidated. For CH3I, energy values of parallel and perpendicular transitions differ from experimental values by 455 and 1156 cm−1, respectively. Effects of fluorination are emphasized, it is found that fluorination increases the gap between Q30 and Q11 transitions and increase is substantially more in aryl iodides than in alkyl iodides. Electronic factors influencing increased I* quantum yield in the photodissociation on fluorination of alkyl iodides is attributed to increased gap between Q30 and Q11 transitions reducing curve crossing probability and for aryl iodides there is additional role by phenyl transitions. A correlation diagram illustrating transitions of aryl iodides is presented.
Human ear tympanum oscillation recorded using a magnetoresistive sensor
Authors: Sosa M. , Carneiro A. A. O. , Baffa O. , Colafemina J. F.
Published: October 2002

A magnetic probe using a commercial magnetoresistive sensor for monitoring the dynamics of the human tympanic membrane has been developed. The method is based on the measurement of the magnetic flux changes produced by the vibrations of a small magnet attached to the tympanic membrane. The system was evaluated with respect to its applicability to detect displacement amplitudes in the tympanum by measurements performed in an excised temporal bone. A sensitivity sufficient to detect vibrations down to about 65×10−9 m was observed for a wide range of frequencies between 200 Hz and 5.0 kHz. Displacement amplitudes of 400 nm on average were detected with an error of ±65 nm.
Canonical parallel tempering simulations of Arn–HF clusters (n=1→12): Thermodynamic properties and the redshift as a function of temperature
Authors: Skone J. H. , Curotto E.
Published: October 2002

A systematic investigation of the thermodynamic and structural properties of Arn–HF clusters in the n=1 to 12 range and comparisons with the corresponding homogeneous Arn+1 reveal that Arn–HF clusters undergo mixing isomerizations. We present evidence that in some cases (n=5, 9, and 10) some isomerizations take place at extremely cold temperatures (T<1 K). We estimate the temperature dependence of the redshift for Arn–HF using a semiclassical stochastic method. We find that the classical redshift depends strongly on temperature and is affected by Ar–HF exchanges. A quantitative structural characterization of the walk allows us to detect the onset of several distinct types of isomerizations for the less stable clusters.
The field-ionization of near-dissociation ion-pair states of I2
Authors: Ridley T. , de Vries M. , Lawley K. P. , Wang S. , Donovan R. J.
Published: October 2002

Using a resonant multiphoton excitation pathway, it is shown that electronic states down to 30 cm−1 below the first ion-pair dissociation threshold of I2 can be efficiently converted from initially prepared well-defined low-J states to long-lived (τd>4 μs), subthreshold zero ion kinetic energy (ZIKE) ion-pair states which are analogous to high, zero electron kinetic energy, Rydberg states. A pulsed electric field is used to dissociate the ZIKE states and produce free-ion pairs (i.e., I++I−). Direct excitation to very high vibrational levels of the ion-pair states is ruled out and polarization data are used to probe the spectroscopic character of the doorway states to free-ion formation. The ion-pair dissociation limit, determined from the extrapolation to zero field of the onset of the prompt I+/I− signal, agrees well with the literature value.
Femtosecond velocity map imaging of concerted photodynamics in CF2I2
Authors: Roeterdink Wim G. , Janssen Maurice H. M.
Published: October 2002

The femtosecond pump–probe technique is used in combination with velocity map ion imaging to study the photodissociation dynamics of CF2I2. Velocity map ion imaging provides the kinetic energy and the angular recoil distribution of the detected fragments. It enables us to distinguish between multiple photoexcitation and dissociation pathways leading to the same ionic fragment. For the dissociation of CF2I2 with delayed femtosecond pulses at 264 and 396 nm, various ionic fragments and dissociation channels are observed. Especially interesting dynamics is observed for the molecular detachment of I2. It is found that at short pump–probe delay (⩽250 fs) I2+ can be formed via a one-photon excitation at 264 nm and subsequent ionization of the dissociating neutral CF2I2 molecule. This excitation pathway produces slow I2+ fragments recoiling predominantly parallel along the polarization of the 264 nm pump laser. At long delay time (⩾500 fs) this pathway is closed and the formation of molecular I2+ proceeds via a two-photon excitation at 264 nm to a highly electronically excited state of the CF2I2 molecule. The molecular detachment of I2 is via a concerted asynchronous dissociation producing a highly internally excited I2* fragment, possibly in the Π3/225d;2g state. The highly excited I2 fragments are ionized by a single 396 nm photon producing I2+ fragments. The kinetic energy of this pathway is higher and the I2+ fragments are recoiling perpendicular with respect to the polarization of the pump laser.
Three-axis lever actuator with flexure hinges for an optical disk system
Authors: Han Chang-Soo , Kim Soo-Hyun
Published: October 2002

A three-axis lever actuator with a flexure hinge has been designed and fabricated. This actuator is driven by electromagnetic force based on a coil-magnet system and can be used as a high precision actuator and, especially as a pickup head actuator in optical disks. High precision and low sensitivity to external vibration are the major advantages of this lever actuator. An analysis model was found and compared to the finite element method. Dynamic characteristics of the three-axis lever actuator were measured. The results are in very close agreement to those predicted by the model and finite element analysis.
Diffusing wave spectroscopy method based on high-speed charge coupled device for nonergodic systems of electrorheological fluids
Authors: Xu J. , Dong X. , Zhang L. F. , Jiang Y. G. , Zhou L. W.
Published: October 2002

Diffusing wave spectroscopy (DWS) measurement has been developed to work with a high-speed charge coupled device (CCD). A real-time measurement of autocorrelation function for a nonergodic system was performed to study statistical interaction between particles of electrorheological fluids. As a test, DWS measurements on an ergodic system were achieved using both a high-speed CCD and single-mode fiber, and the deviation of the characteristic decay times using these two methods is less than 2% for glass bead/silicone oil suspension. In the method of DWS based on a high-speed CCD, the multispeckle measurement enables one to do the ensemble average directly. The CCD with the highest rate of 8000 frames/s makes it possible to investigate the short-time behavior of nonergodic systems. The structure response time is obtained by measuring the light transmittance through samples under different electric fields. By analyzing diffusion coefficient of a sample, the force response time is also obtained.
Momentum flux measuring instrument for neutral and charged particle flows
Authors: Chavers Donald G. , Chang-Díaz Franklin R.
Published: October 2002

An instrument to measure the momentum flux (total pressure) of plasma and neutral particle jets onto a surface has been developed. While this instrument was developed for magnetized plasmas, the concept works for nonmagnetized plasmas as well. We have measured forces as small as 10−4 N on a surface immersed in the plasma where small forces are due to ionic and neutral particles with kinetic energies on the order of a few eV impacting the surface. This instrument, a force sensor, uses a target plate (surface) that is immersed in the plasma and connected to one end of an alumina rod while the opposite end of the alumina rod is mechanically connected to a titanium beam on which four strain gauges are mounted. The force on the target generates torque, causing strain in the beam. The resulting strain measurements can be correlated to a force on the target plate. The alumina rod electrically and thermally isolates the target plate from the strain gauge beam and allows the strain gauges to be located out of the plasma flow while also serving as a moment arm of several inches to increase the strain in the beam at the strain gauge location. These force measurements correspond directly to momentum flux and may be used with known plasma conditions to place boundaries on the kinetic energies of the plasma and neutral particles. The force measurements may also be used to infer thrust produced by a plasma propulsive device. Stainless steel, titanium, molybdenum, and aluminum flat target plates have been used. Momentum flux measurements of H2, D2, He, and Ar plasmas produced in a magnetized plasma device have been performed.
A low noise thermometer readout for ruthenium oxide resistors
Authors: Fixsen D. J. , Mirel P. G. A. , Kogut A. , Seiffert M.
Published: October 2002

The thermometer readout and thermal control system for the Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE) experiment is described, including the design, testing, and results from the first flight of ARCADE. The noise is equivalent to about 1 Ω or 0.15 mK in a second for the RuO2 resistive thermometers at 2.7 K. The average power dissipation in each thermometer is 1 nW. The control system can take full advantage of the thermometers to maintain stable temperatures. Systematic effects are still under investigation, but the measured precision and accuracy are sufficient to allow measurement of the cosmic background spectrum.
Germing surfaces in reaction-diffusion systems? Experiments and a hypothesis
Authors: Hantz Péter
Published: October 2002

Simple inorganic reactions in gels, such as NaOH+CuCl2, NaOH+Cu(NO3)2, and NaOH+AgNO3, are used to obtain complex spatial patterns. When the reactions are running in a thin gel sheet, trapezoid-shaped precipitate regions emerge behind shrinking reaction fronts. Our experimental results suggest that the reaction fronts, which are segments of the borders of the precipitate regions, act as reactive surfaces where an intermediate compound is formed, and the progression of the fronts require a critical concentration of this compound. This phenomenon was modeled by the combination of reaction-diffusion equations and a generalized cellular automata. The most important qualitative features of the patterns have been reproduced by computer simulations.
Exploring the OH+CO→H+CO2 potential surface via dissociative photodetachment of (HOCO)−
Authors: Clements Todd G. , Continetti Robert E. , Francisco Joseph S.
Published: October 2002

Dissociative photodetachment (DPD) of the molecular anion HOCO− is used to probe the potential energy surface for the OH+CO→H+CO2 reaction. The HOCO− anion, formed by electron impact on an expansion of CH4+N2O+CO, is characterized for the first time in these experiments by photoelectron spectroscopy and photoelectron angular distribution measurements. Photodetachment of HOCO− is found to produce H+CO2+e− and OH+CO+e− products in addition to stable HOCO radicals. Ab initio calculations of the energetics and structure of HOCO− and HOCO are consistent with the experimental results and show that photodetachment to the ground electronic HOCO surface samples the vicinity of the HOCO well. The product translational energy distributions observed on the ground state surface are consistent with unimolecular decomposition out of the HOCO well. In addition, direct DPD to a repulsive excited state of HOCO, correlating to ground state OH+CO products is observed.
Disclosing rovibrational couplings and overlaps from irregularities in action spectra: Photodissociation of the 4νCH rovibrational manifold of C2H2
Authors: Sheng Xinzhi , Ganot Yuval , Rosenwaks Salman , Bar Ilana
Published: October 2002

Absorption and free-jet action spectroscopy of states in the region of four quanta of C–H stretching of acetylene (C2H2) around 12 676 cm−1 were studied. Rovibrational excitation combined with 243.135 nm promotion of C2H2 molecules to the upper electronic trans-bent states, Ã 1Au/B̃ 1Bu, and H photofragment ionization generated action spectra measuring the H yield as a function of the excitation wavelength. The findings show that the (1030000) IR bright state of the third C–H stretch overtone has a smaller photodissociation cross section than the (1214000) combination band containing trans-bend mode excitation and lying in its vicinity, due to a favorable Franck–Condon factor for the latter. Certain line pairs accessing similar J′ levels of the (1030000) state show anomalous intensities in the action spectrum, with P transitions excessively enhanced over R transitions. This implies enormous dissociation efficacy as a consequence of Coriolis-type local resonances with nearby states of another band and due to the overlap of the P transitions with another band.
Instrumentation for direct, low frequency scanning capacitance microscopy, and analysis of position dependent stray capacitance
Authors: Lee David T. , Pelz J. P. , Bhushan Bharat
Published: October 2002

We describe instrumentation for scanning capacitance microscopy (SCM), using an atomic force microscope, that is designed to make calibrated, low frequency measurements of tip–sample capacitance and spreading resistance of thin dielectric films. We also characterize spatial variations in stray capacitance Cstray that must be understood before such measurements can be interpreted. Existing SCM circuits are generally optimized for measuring dC/dV, and not for calibrated low frequency measurements of absolute capacitance. Our circuit uses a commercially available current amplifier and low frequency (∼5 kHz) lock-in detection. This circuit adds an inverted, constant amplitude current to suppress the stray displacement current from the large (∼0.5 pF) stray capacitance Cstray between the sample and the mm-sized cantilever–probe assembly. The capacitance noise spectrum is ∼0.35 aF/Hz and is flat down to 1 Hz measurement frequency, with an integrated noise <5 aF integrated over a 1–160 Hz bandwidth. We have also used this instrumentation to identify and characterize significant (>1 fF) variations in Cstray that must be understood in order to accurately measure aF-level variations in the nm-scale tip–sample capacitance. We find that Cstray varies with lateral probe position. This is due to tilting of the probe assembly as the piezoelectric scanner tube bends during scanning. We also find that Cstray varies significantly with probe–assembly height. This causes topography related artifacts in capacitance images of rough surfaces. However, we show that stray capacitance artifacts can be mostly eliminated by properly characterizing position and height dependent variations in Cstray and subtracting them from measured capacitance data.
Pulsed inductive microwave magnetometer
Authors: Kos Anthony B. , Silva Thomas J. , Kabos Pavel
Published: October 2002

We describe the apparatus, software, and measurement procedures for a pulsed inductive microwave magnetometer (PIMM). PIMM can measure the dynamical properties of materials used in recording heads for magnetic storage applications, and it can be used as a general magnetodynamics diagnostic tool. PIMM uses a coplanar waveguide as both a source of fast pulsed magnetic fields and as an inductive flux sensor. Magnetic field pulses are provided by a 10 V, 55 ps risetime pulse generator; a 20 GHz digital sampling oscilloscope is used to acquire the fast pulse data; and orthogonal Helmholtz pairs provide the bias and saturating fields required for the measurement. The system can measure dynamical behavior as a function of several variables, including applied magnetic bias field, magnetic pulsed field amplitude and width, and sample orientation. Using a fast Fourier transform, PIMM can determine the frequency dependence of the complex magnetic permeability, as well as the step and impulse responses of the magnetic system. Data from 50 nm Ni–Fe and rare-earth-doped Ni–Fe thin films are presented.
Automated flexure testing of axially rotated optical fiber gratings
Authors: Bachim B. L. , Gaylord T. K.
Published: October 2002

The design and performance of an automated system for flexure testing of optical fiber gratings is described. In addition to flexing (bending) a fiber grating through a specified curvature range, the system can change the axial rotational orientation of the grating relative to the plane of curvature. Flexure is accomplished by holding the grating against a smooth plastic platform. A linear stage deflects the center of the pinned platform to create a curved surface. Two small weights, hanging on the optical fiber, hold the fiber grating against the curved platform and provide constant tension on the optical fiber over the entire range of curvatures. The fiber grating is axially rotated to a different orientation by returning the platform to zero curvature, removing the weights from the optical fiber, and rotating the optical fiber about its axis using a pair of rotation stages. After replacing the weights on the optical fiber, flexure testing resumes at the new axial rotational orientation. The grating transmission spectrum during flexure is monitored with a broadband source and optical spectrum analyzer. All of these steps are done in an automated fashion (unattended) under computer program control. The testing system allows complete characterization of the fiber grating response for curvatures from 0 to 4 m−1 and for axial rotational orientations from 0° to 360°. Use of this automated test fixture eliminates the need for human intervention during the measurements and greatly decreases the testing time while still allowing complete characterization of the flexure response with axial rotational orientation as a parameter. Additional advantages of the testing system include an absolute zero curvature starting position, an absence of hysteresis effects, and accurate frictionless rotation.
Capacitance dispersion in ion implanted 4H and 6H-silicon carbide
Authors: Evwaraye A. O. , Smith S. R. , Mitchel W. C. , Capano M. A.
Published: October 2002

Nitrogen doped 4H–SiC and 6H–SiC epitaxial layers with net doping concentration of 1.5×1015 cm−3 were implanted with either Al, B, or Ar ions at 600 °C. The energy of the ions was 160 keV and at a dose of 2×1016 cm−2. After annealing at 1600 °C for 5–60 min, Schottky diodes were fabricated on the samples. The measured junction capacitance of ion implanted samples varies with both temperature and frequency. The thermal activation energy determined from the frequency break ωB ranges from 183 to 202 meV. The Ar implanted samples remain n-type and show no capacitive dispersion. Similarly, the junction capacitance of samples doped with Al does not exhibit dispersion. It is suggested that the implantation induced defects play a role in the observed dispersion. The data show that the series resistance is insignificant and does not account for the observed dispersion.
Development of the imaging system of the balloon-borne gamma-ray telescope Máscara Codificada (MASCO)
Authors: Braga João , D’Amico Flavio , Villela Thyrso , Mejı́a Jorge , Fonseca Raphael A. , Rinke Elisete
Published: October 2002

We report laboratory imaging results of a balloon-borne gamma-ray imaging telescope, Máscara Codificada (Portuguese for “coded mask,”) designed to obtain high angular resolution (∼14 arcmin) images of the sky in the 50 keV–1.8 MeV energy range. The instrument incorporates a coded mask with an aperture pattern based on a 19×19-element modified uniformly redundant array (MURA). This pattern belongs to a subclass of MURAs that are almost completely antisymmetrical for 90° rotations with respect to the lower-right corner of the central element, which allows the implementation of an antimask by a single rotation of the whole mask by 90°. The symmetry properties of the MURAs are discussed. The algorithm for determining the position of the gamma-ray interactions on the instrument’s main detector is described and the results of laboratory tests of the imaging system are presented. The mask–antimask subtraction, applied after a flat-fielding procedure, produced a 60% increase in the signal-to-noise ratio of a strong (∼100σ) point source (662 keV photons coming from a Cs137 radioactive source) image by eliminating systematic distortions in the instrumental background measured over the detector plane.
Exactly solvable Ogston model of gel electrophoresis. IX. Generalizing the lattice model to treat high field intensities
Authors: Gauthier Michel G. , Slater Gary W.
Published: October 2002

Traditionally, the Ogston regime is studied solely in the limit of low field intensities. This explains why the theoretical discussion has focused until now on the relative roles of the fractional volume available to the analyte and the subtleties of the gel architecture. Over the past several years, we have developed a lattice model of gel electrophoresis that has allowed us to revisit the fundamental assumptions of the standard Ogston model. In particular, we demonstrated that the fractional free volume is not the relevant parameter for gel sieving. In this article, we continue the development of this model and we generalize our mathematical approach to treat nonvanishing electric field intensities. To do so, we must revisit the way biased random walks are normally modeled by stochastic processes. Straightforward generalizations based on standard Metropolis-like schemes fail at high field intensities. Moreover, our generalization requires the complete decoupling of the spatial directions parallel and perpendicular to the field direction. We show that our novel theoretical approach makes it possible to calculate exact mobilities in the presence of lattice obstacles. Several two-dimensional examples are then studied, including one that includes topological dead ends that act like traps. In the latter case, we recover results very similar to those reported by Serwer et al. [Biopolymers 29, 1863 (1990)] on the trapping electrophoresis of charged spheres in agarose gels. In the absence of such traps, the mobility is shown to be a very weak function of the electric field, thus validating the historical neglect of the field intensity in the development of obstruction models for the Ogston sieving regime of small analytes. Finally, we describe how the present model could be improved to treat more realistic cases and we discuss the problem of the field dependence of the diffusion coefficient during electrophoresis.
Molecular dynamics simulation of liquid N2O4⇌2NO2 by orientation-sensitive pairwise potential. II. Vibrational dephasing of the dissociation mode
Authors: Katō Toshiko
Published: October 2002

Vibrational dephasing of the N-N dissociation mode in equilibrium liquid N2O4⇌2NO2 in the extreme limit of pure N2O4 is studied by classical molecular dynamics simulations of liquid NO2. An OSPP+LJ potential between NO2 molecules, which is a sum of an orientation-sensitive pairwise potential (OSPP) between N-N atoms proposed in Paper I [J. Chem. Phys. 115, 10852 (2001)] and Lennard-Jones potentials between N-O and O-O atoms, has been used in the simulation. The vibrational correlation function and Raman spectrum of the N-N stretching ν3 mode of N2O4 are calculated, and are found to be very sensitive to the well depth De and anisotropy factors of OSPP: Aθ (0⩽Aθ⩽1) for rocking angle between the N-N bond and ONO direction, and Aτ (0⩽Aτ⩽1) for the torsional angle. As Aτ increases in equilibrium liquid N2O4⇌2NO2, the equilibrium shifts to dissociation, and the isotropic Raman band shifts to low frequency and broadens. The OSPP potential for De=0.12×10−18 J, Aθ=0.5, and Aτ=0.1 is found to reproduce both the observed liquid phase equilibrium properties and Raman band shapes (peak frequency, bandwidth, and band asymmetry) of the dissociation mode very well. The long persistent positive correlation in the vibrational frequency fluctuation correlation function Gω(t)=〈Δω(0)Δω(t)〉/〈Δω(0)2〉 is mainly ascribed to the slow energy fluctuation in the dissociation mode. It is concluded that the asymmetry of the ν3 Raman band is due to the scattering by molecular pairs excited in the dissociation mode.
Magneto-optical Kerr effect in the diffracted light of Fe gratings
Authors: Schmitte Till , Westerholt Kurt , Zabel Hartmut
Published: October 2002

The magneto-optical Kerr effect in longitudinal configuration is used to study hysteresis loops of ferromagnetic gratings patterned by electron beam lithography. We study the Kerr effect not only in specular reflection but also off-specular at the intensity maxima of the grating at different orders of diffraction n. The Kerr rotation in saturation increases linearly with the order of diffraction n if the incoming beam is at normal incidence. The shape of the hysteresis curves changes for special orders of diffraction, indicating an enhanced sensitivity for the formation of magnetic domains close to remanence. The nth order of diffraction is sensitive to the nth order Fourier component of the magnetization distribution.
Electrical isolation of InGaP by proton and helium ion irradiation
Authors: Danilov I. , de Souza J. P. , Boudinov H. , Bettini J. , de Carvalho M. M. G.
Published: October 2002

Formation of electrical isolation in n- and p-type In0.49Ga0.51P epitaxial layers grown on semi-insulating GaAs substrates was investigated using proton or helium ion irradiation. Sheet resistance increases with the irradiation dose, reaching a saturation level of ≈109 Ω/□. The results show that the threshold dose necessary for complete isolation linearly depends on the original carrier concentration either in p- or n-type doped InGaP layers. Thermal stability of the isolation during postirradiation annealing was found to increase with accumulation of the ion dose. The maximum temperature at which the isolation persists is ≅500 °C.