bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of fetal weight based on ultrasonic femur length after the second trimester
Authors: Honarvar Mehrdad , Allahyari Mahboobeh , Dehbashi Sedigheh
Published: October 2002

Objective: The ultrasonic measurement of the fetal femur length is a sensitive and precise variable for estimation of fetal growth and development. The objective of this study is to predict fetal weight in fetuses of more than 24 weeks gestation by ultrasound measurement of the femur length. Method: In this study, pregnant mothers were identified by the criteria of normalities, such as: well‐known LMP, regular menstrual cycles, no use of OCP for the last 3 months, no use of alcohol or cigarettes, no drug abuse, no history of diabetes or chronic HTN. Multiple gestations, congenital anomalies and still‐births were excluded. Birth‐weight measurements (adjusted for maternal age, baby's sex, parity and week of gestation) were taken immediately after birth. Result: The relation between fetal weight and fetal femur length has been determined by cross‐sectional analysis of 900 normal fetuses (≥25 weeks gestation) using real time ultrasonography. Mathematical modeling of the data has demonstrated that the femur growth curve is non‐linear beyond 24 weeks gestation. With the aid of a scientific calculator the data were analyzed and a simple second‐grade equation has been derived: EFW (kg)=0.042FL2 (cm)+0.32FL−1.36, S.D.∼±235 g (Honarvar's Formula 2). With the use of this data, the error in estimation of EFW given FL is ±235 g. Conclusion: This simple, new and accurate equation appears to be clinically reliable and easy to use and suggests that previous normal ultrasonic fetal femur length curves for another population may underestimate or overestimate normal fetal weight for the Iranian population. Thus, our formula is an excellent means to estimate true fetal weight.
Prenatal diagnosis of twin–twin transfusion syndrome complicated with hydrops fetalis at 14 weeks of gestation
Authors: Su R.‐M , Yu C.‐H , Chang C.‐H , Yang H.‐B , Chang F.‐M
Published: October 2002

Twin–twin transfusion syndrome (TTTS) may complicate multiple pregnancy. Monochorionic discordant twins with oligohydramnios and polyhydramnios may be diagnostic. Hydrops fetalis is particularly ominous. All the signs can appear independently at any stage of gestation. However, TTTS with hydrops fetalis in early pregnancy is rare. We report here a case of TTTS complicated with hydrops fetalis diagnosed at 14 weeks of gestation. Our case may be one of the earliest cases of the prenatal diagnosis of TTTS complicated with hydrops fetalis in the literature.
Chronic pelvic pain: defining the scope of the problem
Authors: Duffy S
Published: October 2002

Objective: To define the scope of the problems associated with chronic pelvic pain (CPP) and optimize management. Method: Clinical trial results and healthcare utilization data from the literature were reviewed. Results: Recent evidence suggests that a large percentage of women experience CPP. While no etiology tends to be found in the majority of these women, the annual cost for diagnosing and treating CPP seems considerable. The management of patients with negative laparoscopies constitutes a clinical challenge. While surgical and medical therapy have a role in CPP, there appears to be no 100% effective cure. Conclusions: There is no consensus on management of patients with no visible pathology and chronic pelvic pain. Physicians should select a treatment for CPP that will be the least complicated and least risky and will deliver speedy symptomatic relief.
Role of a symptom‐based algorithmic approach to chronic pelvic pain
Authors: Winkel C.A
Published: October 2002

Objective: Chronic pelvic pain (CPP) is a disorder that has a significant impact on the patient's quality of life. Laparoscopic diagnosis can be disappointing, and recurrence is common after surgical treatment. A symptom‐based algorithmic approach to treatment of CPP is presented that is safe and cost‐effective. Methods: This approach is oriented towards making a potential clinical diagnosis of endometriosis. It relies on a structured evaluation of the patient and administration of medical therapy including GnRH agonists to selected patients. Evaluation begins with a history and physical examination; selected cases receive specific therapy. Non‐responders undergo appropriate laboratory and imaging studies. If results remain negative, it is possible to make a clinical diagnosis of endometriosis and begin empiric treatment. Results: Early results strongly indicate that using this approach allowed clinicians to make highly accurate diagnoses (correct in 85–90% of cases). Conclusion: Use of this approach will minimize the need for surgery.
Abstract: Avoidance of radiation injuries from medical interventional procedures, ICRP Publication 85
Authors: Valentin J.
Published: October 2002

Interventional radiology (fluoroscopically-guided) techniques are being used by an increasing number of clinicians not adequately trained in radiation safety or radiobiology. Many of these interventionists are not aware of the potential for injury from these procedures or the simple methods for decreasing their incidence. Many patients are not being counselled on the radiation risks, nor followed up when radiation doses from difficult procedures may lead to injury. Some patients are suffering radiation-induced skin injuries and younger patients may face an increased risk of future cancer. Interventionists are having their practice limited or suffering injury, and are exposing their staff to high doses.

In some interventional procedures, skin doses to patients approach those experienced in some cancer radiotherapy fractions. Radiation-induced skin injuries are occurring in patients due to the use of inappropriate equipment and, more often, poor operational technique. Injuries to physicians and staff performing interventional procedures have also been observed. Acute radiation doses (to patients) may cause erythema at 2 Gy, cataract at 2 Gy, permanent epilation at 7 Gy, and delayed skin necrosis at 12 Gy. Protracted (occupational) exposures to the eye may cause cataract at 4 Gy if the dose is received in less than 3 months, at 5.5 Gy if received over a period exceeding 3 months.

Practical actions to control dose to the patient and to the staff are listed. The absorbed dose to the patient in the area of skin that receives the maximum dose is of priority concern. Each local clinical protocol should include, for each type of interventional procedure, a statement on the cumulative skin doses and skin sites associated with the various parts of the procedure. Interventionists should be trained to use information on skin dose and on practical techniques to control dose. Maximum cumulative absorbed doses that appear to approach or exceed 1 Gy (for procedures that may be repeated) or 3 Gy (for any procedure) should be recorded in the patient record, and there should be a patient follow-up procedure for such cases. Patients should be counselled if there is a significant risk of radiation-induced injury, and the patient's personal physician should be informed of the possibility of radiation effects. Training in radiological protection for patients and staff should be an integral part of the education for those using interventional techniques. All interventionists should audit and review the outcomes of their procedures for radiation injury. Risks and benefits, including radiation risks, should be taken into account when new interventional techniques are introduced.

A concluding list of recommendations is given. Annexes list procedures, patient and staff doses, a sample local clinical protocol, dose quantities used, and a procurement checklist.
The role of liver biopsy in chronic hepatitis C
Authors: Dienstag Jules L.
Published: October 2002

The report of the 1997 National Institutes of Health Consensus Development Conference on hepatitis C endorsed pretreatment liver biopsy. We revisit the following questions: Does liver histology help determine the urgency of, and predict the likelihood of response to, antiviral therapy, and can surrogate markers supplant histological assessment? Because the rate of progression of chronic hepatitis C is influenced by baseline histological grade/stage, patients can be stratified into those with moderate to severe hepatitis, who merit imminent therapy, and those with mild hepatitis, in whom therapy can be postponed until more effective/tolerable treatments become available. Less advanced baseline histology has been shown to be an independent predictor of responsiveness to antiviral therapy. Although the predictive value of biopsy is insufficient to withhold therapy from patients with advanced fibrosis, baseline biopsy helps gauge expectations for the outcome of therapy. Reports have been published recently suggesting that laboratory markers can predict distinctions between low-grade fibrosis and therapy-indicating septal fibrosis/cirrhosis. These indices, however, are insufficiently reliable to predict histological distinctions in populations with varying prevalences of fibrosis/cirrhosis or to provide anything more than broad qualitative distinctions, far short of the potential information in a liver biopsy. For most patients, the value of pretreatment liver biopsy outweighs its risks, provides information about the urgency of treatment, and should be retained. Studies to identify noninvasive laboratory markers of histological activity and stage, especially genetic predictors of accelerated disease progression, command a high priority.
The burden of hepatitis C in the United States
Authors: Kim Ray W.
Published: October 2002

According to the third National Health and Nutrition Examination Survey (NHANES), 3.9 million of the U.S. civilian population have been infected with hepatitis C virus (HCV), of whom 2.7 million (74%) have chronic infection. Hepatitis C virus infection is most common among non-Caucasian men, ages 30 to 49 years. Moreover, the prevalence of antibody to hepatitis C virus in groups not represented in the NHANES sample, such as the homeless or incarcerated, may be as high as 40%. The age-adjusted death rate for non-A, non-B viral hepatitis increased from 0.4 to 1.8 deaths per 100,000 persons per year between 1982 and 1999. In 1999, the first year hepatitis C was reported separately, there were 3,759 deaths attributed to HCV, although this is likely an underestimate. There was a 5-fold increase in the annual number of patients with HCV who underwent liver transplantation between 1990 and 2000. Currently, more than one third of liver transplant candidates have HCV. Inpatient care of HCV-related liver disease has also been increasing. In 1998, an estimated 140,000 discharges listed an HCV-related diagnosis, accounting for 2% of discharges from non-federal acute care hospitals in the United States. The total direct health care cost associated with HCV is estimated to have exceeded $1 billion in 1998. Future projections predict a 4-fold increase between 1990 and 2015 in persons at risk of chronic liver disease (i.e., those with infection for 20 years or longer), suggesting a continued rise in the burden of HCV in the United States in the foreseeable future.
Noninvasive monitoring of patients with chronic hepatitis C
Authors: Fontana Robert J. , Lok Anna S. F.
Published: October 2002

Hepatic fibrosis is the main determinant of clinical outcomes of chronic hepatitis C. Liver histology is frequently considered the gold standard for assessing hepatic fibrosis. However, liver biopsy is associated with sampling error, interobserver variability, and potential complications. Thus, there is a need for simple, inexpensive, and reliable noninvasive means to assess disease severity in patients with chronic hepatitis C. Clinical examination is unreliable in differentiating different stages of compensated liver disease. Among the routine laboratory tests, decreased platelet count, increase in the ratio of aspartate to alanine aminotransferase (AST/ALT), and prolonged prothrombin time are the earliest indicators of cirrhosis and portal hypertension. Individual serum fibrosis markers have limited accuracy in predicting hepatic fibrosis. Indices composed of a panel of markers correlate better with histological fibrosis, but their reliability requires further validation. Currently, noninvasive monitoring of patients with chronic hepatitis C relies on clinical evaluation, routine laboratory tests, and ultrasound and endoscopic surveillance in patients with cirrhosis. Initial evaluation should focus on assessment of activity and stage of liver disease for prognostication and decisions regarding treatment, and to rule out coinfections and other causes of liver disease. Subsequent follow-up should focus on detection of liver disease progression and the need for treatment. The frequency of monitoring and the tests used will depend on the patient’s age, stage of liver disease, and comorbid conditions. There is an urgent need to develop and validate noninvasive tests that can accurately reflect the full spectrum of hepatic inflammation and fibrosis in chronic hepatitis C.
Zero-electron-kinetic-energy photoelectron spectroscopy of transition-metal—ether complexes: Y-O(CH3)2, Y-O(CD3)2, Y-[O(CH3)2]2, and Y-[O(CD3)2]2
Authors: Rothschopf Gretchen K. , Li Shenggang , Yang Dong-Sheng
Published: October 2002

The yttrium complexes with one and two dimethyl ethers and their deuterated derivatives are prepared with laser vaporization molecular beam techniques, identified with photoionization time-of-flight mass spectrometry, and investigated with pulsed-field-ionization zero-electronkinetic-energy (ZEKE) photoelectron spectroscopy and ab initio calculations. Adiabatic ionization potentials and yttrium-oxygen stretch and ether-based vibrations are measured for the 1:1 and 1:2 complexes. Fermi interactions are observed from the ZEKE spectra of the 1:1 species. The ground electronic states of the monoligand complexes are determined to be A22 for the neutral and A11 for the singly charged positive ion, both in C2v symmetry, with yttrium binding to oxygen. The coordination of a second ether forms a diligand complex with a linear oxygen-yttrium-oxygen configuration. This is the first electronic-vibrational spectroscopic study of yttrium-polyatomic molecule complexes and weakly bound metal complexes with two or more polyatomic molecules.
The use of a Shack–Hartmann wave front sensor for electron density characterization of high density plasmas
Authors: Baker K. L. , Brase J. , Kartz M. , Olivier S. S. , Sawvel B. , Tucker J.
Published: October 2002

This article examines the use of a Shack–Hartmann wave front sensor to accurately measure the line-integrated electron density gradient formed in laser-produced and Z-pinch plasma experiments. The minimum discernable line-integrated density gradient is derived for the Shack–Hartmann wave front sensor, as well as its range of applicability. A laboratory comparison between a Shack–Hartmann wave front sensor and a Twyman–Green interferometer is also presented. For this comparison, a liquid-crystal spatial-light modulator is used to introduce a spatially varying phase onto both of the wave front sensors, simulating a phase profile that could occur when a probe passes through a plasma. The phase change measured by the Shack–Hartmann sensor is then compared directly with the Twyman–Green interferometer. In this article, the merits associated with the use of a Shack–Hartmann sensor are discussed. These include a wide dynamic range, high optical efficiency, broadband or low coherence length light capability, experimental simplicity, two-dimensional gradient determination, and multiplexing capability.
He discharge lamp for photoemission experiments with radioactive materials
Authors: Durakiewicz Tomasz , Arko Al , Joyce John J. , Moore David P. , Graham Kevin
Published: October 2002

A simple He discharge lamp is described. The lamp is designed specially for photoemission measurements performed on radioactive materials, mainly Pu and Pu compounds. The lamp construction allows easy single-use assembly/disassembly of the discharge tube with minimum risk of radiological contamination, minimum amount of waste generated, air cooling capability, very good He II/He I ratio at low He pressures, and stable operation for at least 200 h. Thanks to the high brightness in the He II range we were able to observe the He IIβ, He IIγ, and even He IIε features in the PuIn3 photoemission spectrum. Total cost of parts used to produce the discharge tube is less than $300, so that the cost of operation is less than $1.5/h.
Performance of a Mott detector for undulator-based spin-resolved spectroscopy
Authors: Huang D. J. , Wu W. P. , Chen J. , Chang C. F. , Chung S. C. , Yuri M. , Lin H.-J. , Johnson P. D. , Chen C. T.
Published: October 2002

To measure spin-polarized core-level electron spectra, a spectrometer equipped with a highly efficient retarding-potential Mott spin polarimeter using undulator-based soft-x-ray beamlines has been set up. With a thin film of Au as a target this polarimeter has an efficiency estimated to be ∼2×10−4. The performance of this system for spin-polarized spectroscopy has been tested using core-level spin-polarized photoemission of magnetic and nonmagnetic thin films excited with linearly and circularly polarized light, respectively. Measurements using a new spin-resolved absorption technique are also discussed.
A gold film detector for radial profile measurement of plasma density by using a gold neutral beam probe
Authors: Ishii K. , Takemura Y. , Fueki A. , Hagisawa K. , Kojima A. , Itakura A. , Yoshikawa M. , Katanuma I. , Yatsu K.
Published: October 2002

A gold film detector was developed in order to measure the plasma density profile by use of the gold neutral beam probe. The detector is a kind of neutral beam detector composed of a rectangular entrance collimator, two sets of grid plates, a gold thin film, a quartz backing, and a microcarbon coated copper plate. The secondary electrons emitted from the gold film were utilized for the neutral beam detection. The yield curves of the secondary electrons were measured as a function of the incident angle and electron energy in both cases of the gold neutral probing beam and ultraviolet ray injection. Time evolution of the plasma line density was measured by adjusting the incident angle and adding a beam chopping method. The result was in good agreement with the line density measured by a microwave interferometer. It was found that this film detector was quite useful in the viewpoint of simultaneous measurements of the electrostatic potential and plasma density profiles.
Electrostatic electron analyzer with 90° deflection angle
Authors: Vattuone L. , Rocca M.
Published: October 2002

We demonstrate the feasibility of a new type of electrostatic cylindrical analyzer terminated with plates with focus at 90° also in the presence of significant space charge. The transmission function is determined by numerical simulation of the trajectories after a full three-dimensional solution of the Poisson problem with boundary condition by an iterative finite difference algorithm. This device may allow a new generation of spin polarized electron energy loss spectroscopy experiments.
A detection system for three-dimensional visualization of cosmic muons trajectories
Authors: Marinho P. R. B. , Barbosa A. F.
Published: October 2002

A detection system for measuring the direction of cosmic muons is presented. The detector is composed by two multiwire proportional chambers 55 mm apart from each other. These chambers operate as two independent subdetectors in coincidence. Each subdetector provides two-dimensional (2D) localization of ionizing events making use of a single X and Y cathode structure for position readout. 2D localization is achieved by associating one delay line to each spatial coordinate. The trajectory is reconstructed from the two pairs of coordinates measured in the subdetector planes. Signals related to the X and Y coordinates of ionizing events are electronically processed and recorded by a data acquisition interface connected to a host personal computer (PC). A user interface software shows the trajectories of ionizing events in a three-dimensional graphic window. Cosmic particles trajectories are visualized in real time. Results are shown that characterize the system performance. The angular and length distributions for measured and simulated muon trajectories are also presented. The obtained results show that, besides the educational purpose of showing real time cosmic ray trajectories, the presented system is also suitable for studying physical properties of cosmic muons.
A fast position sensitive microstrip-gas-chamber detector at high count rate operation
Authors: Dolbnya I. P. , Alberda H. , Hartjes F. G. , Udo F. , Bakker R. E. , Konijnenburg M. , Homan E. , Cerjak I. , Goedtkindt P. , Bras W.
Published: October 2002

Testing of a newly developed position sensitive high count rate microstrip gas chamber (MSGC) detector at high count rate operation has been carried out at the Dutch–Belgian x-ray scattering beamline at the European Synchrotron Radiation Facility (Grenoble, France) with a high intensity x-ray beam. The measurements show local count rate capabilities up to ∼4.5×105 counts/s/channel. Experimental data taken with this detector are also shown. These tests show that both time resolution down to 1.5 ms/frame and a reliable operation at high counting rates can be achieved.
Design and implementation of a high-resolution, high-efficiency optical spectrometer
Authors: Utter S. B. , Crespo López-Urrutia J. R. , Beiersdorfer P. , Träbert E.
Published: October 2002

We present the design, implementation and testing of a high-efficiency, high-resolution transmission grating spectrometer for measurements of near-ultraviolet to visible-range spectra of light from an electron beam ion trap, where geometry is constrained. The system consists of two 5 in. diameter f/4.6 achromatic lenses, a 6 in. diameter transmission grating ion-beam etched in fused silica, and a thinned, backilluminated CCD detector. The simple design minimizes the number of optical components, each with optimal throughput and high efficiency. Using a 30 μm wide entrance slit, a resolving power (λ/Δλ) of 15 400 at λ≈3850 Å has been demonstrated. The features and limitations of the instrument have been explored and an in situ calibration technique for use on the Livermore EBIT-II and SuperEBIT electron beam ion traps has been developed.
New type audio frequency ion source
Authors: Ragheb M. S. , Zakhary S. G.
Published: October 2002

In this work, a new miniature type audio frequency (AF) (10 up to 100 kHz) of capacitive discharge type ion source has been constructed. The source is featured with its high output intensity and its small size. The optimized working condition of the source is defined at certain discharge pressure (0.2 Torr) and certain frequency (15 kc/s) of the audio power supply. At this optimum operating condition of pressure and frequency of the AF supply, the source yields an ion current up to 25 mA and electron current up to 60 mA at low extraction voltage (V=50 up to 150 V). The extracted ion current is found to mainly depend on the discharge pressure and frequency of the audio supply.
Itô diffusions on hypersurfaces with application to the Schwarz-P surface and nuclear magnetic resonance theory
Authors: Håkansson P. , Persson L. , Westlund P.-O.
Published: October 2002

This work presents a new Brownian dynamics simulation method of translational diffusion on curved surfaces. This new method introduce any implicit defined surface into the stochastic differential equation describing Brownian motion on that surface. The surface curvature will thus enter the force term (A) in the stochastic differential equation dXt=A(Xt)dt+B(Xt)dWt describing an Itô process. We apply the method calculating time correlation functions relevant in nuclear magnetic resonance (NMR) relaxation and translational diffusion studies of cubic phases of lyotropic systems. In particularly we study some bicontinuous cubic liquid crystalline phases which can be described as triply periodic minimal surfaces. The curvature dependent spin relaxation of the Schwarz-P minimal surface is calculated. A comparison of relaxation is made with the more complex topology of the Neovius surface which is another minimal surface in the same space group, and with parallel displacement of the minimal surface which thus results in a nonminimal surface. The curvature dependent relaxation effects are determined by calculating the translational diffusion modulated time-correlation function which determine the relaxation rates of a quadrupole nuclei residing in the water–lipid interface. The results demonstrates that spin relaxation data can provide quantitative information about micro-structure of biocontinuous cubic phases and that it is sensitive to the topology of the surface and to parallel displacement of the model surface. Consequently, spin relaxation may be used as a complement to x-ray diffraction in order to discriminate between different microstructures. It is concluded that fast and accurate computer simulations experiments is needed to be able to interpret NMR relaxation experiments on curved surfaces.
Determination of critical length scales and the limit of metastability in phase separating polymer blends
Authors: Lefebvre A. A. , Lee J. H. , Balsara N. P. , Vaidyanathan C.
Published: October 2002

Liquid–liquid phase separation in polymethylbutylene/polyethylbutylene blends near the metastability limit was studied using small angle neutron scattering (SANS). Our objective was to study the relationship between quench depth and Rc, the lower limit for the length scale of the structures formed during the early stages of the phase transition (nuclei). During the early stage of phase separation, the SANS profiles merged at a time-independent critical scattering vector, qc. We discuss different methods for estimating qc, and present arguments for the scaling relationship, Rc∼1/qc. The theory of Cahn and Hilliard predicts that in metastable blends Rc increases with increasing quench depth, and diverges at the spinodal. In contrast, our experimental measurements showed Rc increases with decreasing quench depth, and the location of the point where Rc diverges lies between the binodal and the spinodal. Some aspects of our results are addressed in recent theoretical work of Wang and Wood [J. Chem. Phys. 117, 481 (2002)], wherein the effects of fluctuations on the binodal and spinodal curves in polymer blends are incorporated.
Fluctuation mediated phase separation in polymer blends near the limit of metastability
Authors: Lefebvre A. A. , Lee J. H. , Balsara N. P. , Vaidyanathan C.
Published: October 2002

The evolution of the structure factor of off-critical polyolefin (polymethylbutylene/polyethylbutylene) blends quenched from the homogeneous state to states near the limit of metastability was studied by small angle neutron scattering. The Cahn–Hilliard–Cook theory was used to organize the data in terms of three time-independent parameters that depend on the scattering vector, q: S0(q), the initial structure factor, St(q), the terminal structure factor, and R(q), a kinetic parameter that indicates the time scale for the transformation from S0(q) to St(q). These three parameters change systematically with quench depth. Changes in the structure factor S(q,t) are only observed in the q values smaller than a critical scattering vector, qc. At small quench depths, qc is obtained because R(q)→0 as q→qc. At deeper quenches, qc is obtained because St(q)→S0(q) as q→qc. Scattering characteristics at q<qc such as scattering peaks or the lack thereof arise due to the interplay between R(q) and St(q).
Evaluation of a high-speed signal-averager for sensitivity enhancement in radio frequency Fourier transform electron paramagnetic resonance imaging
Authors: Devasahayam N. , Murugesan R. , Yamada K. , Reijnders K. , Mitchell J. B. , Subramanian S. , Krishna M. C. , Cook J. A.
Published: October 2002

A commercially available high-speed, digital signal-averager is integrated into an existing time-domain radio frequency (rf) electron paramagnetic resonance (EPR) spectrometer/imager. Sensitivity enhancement by the integrated system is estimated by coherent averaging of free induction decay signals, obtained from narrow-line EPR spin probes, and its performance is compared with that of an existing custom-built averager. For the existing custom-built “Analytek” averager, the minimum realizable trigger rate was 50 kHz, whereas for the commercial EG&G 9826 system, due the spectrometer constraints, we set the retrigger rate to 133 kHz. Very short summing and down loading times of the latter enable good temporal resolution in phantom as well as in vivo rf Fourier transform EPR images, obtained by the single point imaging (SPI) modality. For two-dimensional and three-dimensional imaging using the SPI mode, a saving of time by a factor of >2 could be achieved with the EG&G system compared with the Analytek.
A reflectance spectrofluorimeter for real-time spectral diagnosis of disease
Authors: Müller Markus G. , Wax Adam , Georgakoudi Irene , Dasari Ramachandra R. , Feld Michael S.
Published: October 2002

We have developed a portable multiexcitation dye laser system pumped by a 308 nm excimer laser, which can collect fluorescence spectra at 11 excitation wavelengths and a white light reflectance spectrum in less than 200 ms. The system is designed to be used in a hospital setting for in vivo tissue analysis based on fluorescence and reflectance spectroscopy. A specially designed optical fiber probe with SMA couplers facilitates easy alignment, important in a clinical setting. An intensified charge coupled device camera provides fast data acquisition with large signal-to-noise (S/N) ratio. The optical and electronic systems are controlled with LABVIEW, which is well suited for real time analysis, to extract diagnostic information. We present typical spectra that demonstrate the large excitation-emission wavelength range over which spectra can be acquired with very good S/N ratios.
Instrument for studies of homogeneous and heterogeneous ice nucleation in free-falling supercooled water droplets
Authors: Wood Stephen E. , Baker Marcia B. , Swanson Brian D.
Published: October 2002

We have developed an instrument to study the homogeneous and heterogeneous freezing of droplets in free fall. The advantages of this technique are high repetition rates, telemicroscopic imaging of frozen and unfrozen droplets, and the elimination of possible contamination and nucleation effects induced by substrates. Droplets are ejected at a rate of about 5 per s from a generator at the top of a temperature controlled freezing tube. They fall in a stream down the center of the tube as their images are recorded using video-telemicroscopy. The fraction of drops frozen is measured as a function of height (and, hence, as a function of temperature) by illuminating slices of the stream with linearly polarized laser light and monitoring the depolarization of the backscattered light; ice particles depolarize the scattered light while the liquid droplets do not. The use of depolarization for phase discrimination is unique in this context. We have demonstrated the usefulness of our instrument with pure water droplets and droplets containing water and a bionucleant (Pseudomonas Syringae, or “SNOMAX”). The observed homogeneous freezing temperature of pure water droplets is about −37.0 °C while heterogeneously frozen water droplets containing SNOMAX freeze at around −8.0 °C. We find that the homogeneously frozen pure water droplets tend to be more irregular and bumpy than those heterogeneously frozen.
A calcium vapor cell for atomic spectroscopy
Authors: Huang Mao-Sheng , Lu Mao-Hong , Shy Jow-Tsong
Published: October 2002

A calcium vapor cell used in laser spectroscopy usually suffers from calcium coating on the cell windows. To solve the problem, we add two mirrors in the cell to reflect the laser beam, then the calcium will coat on these mirrors instead of on the windows. Calcium coating degrades the reflectivity of the mirrors at the beginning, but the mirrors become calcium mirrors after a certain period of coating and their reflectivity will not change by further calcium coating. Using this cell in a conventional saturated-absorption spectroscopy, the observed saturated-absorption peak at 657 nm is about 2.4% of the probe beam power and its linewidth is below 300 kHz. Therefore, a portable secondary calcium-wavelength standard at 657 nm having an accuracy better than 1×10−11 is possible. In addition, our cell has a continuous working time longer than 3 d and it can be easily extended to 10 d.
The effect of electrical parameters on the simulated spark gap discharge current
Authors: Golnabi Hossein
Published: October 2002

In this article, the effects of electrical parameters on the spark gap discharge current formation are reported. Using the finite element method to solve for the electric potential and field simulates the discharge process in two- and three-electrode spark gaps using nitrogen gas. The effects of the electrical components on the discharge current buildup and switch closing time for the two switches are investigated. Simulation results for different values of series resistance, capacitance, and inductance are presented for the two-electrode spark gap. In the case of three-electrode spark gaps, the effects of the series resistance, inductance, capacitance, and the resistance and the capacitance of the trigger branch circuit on the discharge current are investigated. The effect of the trigger voltage on the discharge current buildup and arc formation time is also described for the triggered spark gap trigatron. It has been noticed that for both spark gaps the series inductance could severely limit the current buildup rate.
Multiple channel superconducting quantum interference device controller using a digital signal processor
Authors: Limketkai B. , Granger J. , Weilert M. , Hahn Inseob
Published: October 2002

We report on the design, performance, and limitations of an improved multiple superconducting quantum interference device (SQUID) controller based upon a digital signal processor. The flux noise level of the dc SQUID controller system is comparable with the commercial analog system, ∼4 μΦ0/Hz1/2 at 100 Hz. The measured maximum slew rate of the system is approximately 800 Φ0/s. The current system could control up to five SQUID channels.
High pressure circulating pump
Authors: Van Doorn John , Mather Alan E.
Published: October 2002

The design of a high pressure circulating pump operated by external magnets is described. It is an improvement of the pump of Ruska et al. [Rev. Sci. Instrum. 41, 1444 (1970)]; it incorporates features such as continuous pumping and reduced wear of the magnets and is suitable for corrosive mixtures containing H2S.
Solar and Heliospheric Observatory/Solar Ultraviolet Measurements of Estimated Radiation ultraviolet array detector distortion correction
Authors: Moran Thomas G.
Published: October 2002

We present the technique used to correct the geometric distortion in the Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Estimated Radiation (SOHO/SUMER) ultraviolet spectrograph images. Electric and magnetic fields within the SUMER crossed delay line detectors and optical misalignment within the SUMER spectrograph cause focal plane image distortion, which leads to errors in wavelength and position measurements if not corrected. A high degree of precision is required in geometric correction in order to achieve the required accuracy in solar ultraviolet line position measurements. We characterize the distortion using a combination of laboratory and in situ measurements to compute tables of horizontal and vertical pixel shift vectors and correct the distorted frame by interpolation to within 0.11 pixel rms error in wavelength pixel and 0.25 pixel rms error in spatial pixel. The correction allows measurements of line-of-sight solar ion velocities with 1 km/s accuracy.
A Bragg scattering spectrometer for studying crystallization of colloidal suspensions
Authors: Francis P. S. , Martin S. , Bryant G. , van Megen W. , Wilksch P. A.
Published: October 2002

A light scattering spectrometer is described that is used for the study of crystallization in hard sphere colloidal suspensions. Collimated laser light is Bragg scattered from the crystals as they form, and the diffracted light is focused by a liquid filled hemispherical lens onto low cost charge coupled device array detectors that are rotated about the optical axis to average the intensities around the whole Debye–Sherrer cone of scattered light. The temperature of the sample can be controlled, and this is utilized to control the amount of scattering from the sample. The spectrometer exploits the refractive index match of the colloidal particles, the solvent, the bath liquid, and the glass used for both the sample bottle and the hemispherical lens. Parameters measured are crystallization rate, the amount of crystal formed, and the average lattice spacing, all as functions of time. Results presented show that this spectrometer gives insight into the crystallization process more than 1 order of magnitude of time earlier than previous light scattering experiments, leading to understanding of the crystallization process.
Ultrasonic frequency driven long plasma column
Authors: Ragheb M. S.
Published: October 2002

A study of argon gas stimulated at ultrasonic frequencies reveals different characteristic aspects. The plasma is created in a 50 cm tube with an effective work length of 25 cm. In order to initialize and maintain the process, plasma discharge parameters, namely, current, voltage, power, pressure, and frequency are studied and optimized. The data obtained show that in order to maintain a plasma discharge specific current, it would be sufficient to apply a higher frequency and lower voltage, whereas the current, at higher frequency and higher voltage, would be higher. Moreover the increase of the discharge voltage, frequency, and pressure increases the discharge current and consequently the discharge power. On the other hand along the half length of the tube, the plasma parameters; temperature, density, mean electron energy, and Debye length are studied and evaluated by means of a floating double Langmuir probe system. Moving from the hot electrode towards the grounded one, the electron temperature increases while the electron density decreases. The plasma temperature measured is 3–20 eV and the average plasma density is on the order 1011 cm−3, according to the pressure, the frequency, and the discharge voltage applied. The plasma source has low power consumption where, for normal operation of 25 W, the discharge voltage VD is 300 V, and the discharge current Ip is 80 mA. Away from gas breakdown, the maximum power absorbed is found to be 60 W, where VD=500 V and Ip=120 mA. A plasma phenomenon of alternatively dark and bright regions appear in the vessel, and are easily seen along the plasma tube, denoting the response of both the electron temperature and the electron density to an oscillatory behavior. The range of the applied pressure, discharge voltage, frequency, current, and power consumed inside the vessel are, respectively, 0.01–0.25 Torr, 50–500 V, 10–100 kHz, 1.5–160 mA, and 5–60 W. The formed plasma is durable, until it would be discarded. Physically it has a pale pink color that becomes brighter by increasing the discharge voltage.
The secondary response distortion in transient absorption spectroscopy
Authors: Cline Jason A. , Jonah Charles D. , Bartels David M.
Published: October 2002

Transient absorption spectroscopy has been used for many years to record the kinetics and spectra of transient chemical species following a short photolysis or radiation pulse. Linearity of the detector is always important, but cannot always be assumed for experiments on a submicrosecond timescale, and should never be assumed on a subnanosecond timescale. In addition, fast photodiode detectors often exhibit a delayed secondary response, which depends on the wavelength of excitation. In this article we demonstrate the distortions introduced by secondary detector response with some examples from pulse radiolysis. A method for calibration is demonstrated using the broad visible/near-infrared absorption of solvated electrons in water. A standard decay shape is constructed from stroboscopic measurements at short time, and from the (400–800 nm) response of an EG&G FND100Q silicon diode at times greater than 10 ns. The calibration is applied to the FND100Q silicon diode, and to GMP566 germanium and GAP520 InGaAs diodes manufactured by Germanium Power Devices, Inc. Correction of the latter diode is needed to record a visible/near infrared spectrum of solvated electrons in heavy water at elevated temperatures.
A differentially pumped electrostatic lens system for photoemission studies in the millibar range
Authors: Ogletree D. Frank , Bluhm Hendrik , Lebedev Gennadi , Fadley Charles S. , Hussain Zahid , Salmeron Miquel
Published: October 2002

A high pressure photoemission system is described that combines differential pumping with an electrostatic lens system. This approach allows optimized differential pumping without loss of signal, thereby increasing the high-pressure performance by at least 2 orders of magnitude compared to passive differential pumping systems. A general analysis of aperture-based high-pressure photoemission is presented, followed by a description of the prototype system which has operated at pressures up to 7 mbar on a synchrotron beamline. Using this approach, photoemission experiments should be possible up to 100 mbar. Example data are presented for dielectric samples in gas atmospheres, for a copper catalyst under reaction conditions, and for liquid water in equilibrium with its vapor.
Hyperthermal ion beam system optimized for studying the effects of kinetic energy on thin-film growth
Authors: Pomeroy J. M. , Couture A. J. , Murty M. V. R. , Butler E. N. , Cooper B. H.
Published: October 2002

A hyperthermal and low-energy ion beam (10–1000 eV) optimized for studying morphological trends in epitaxial metal thin films as a function of atomic kinetic energy has been built and characterized. The ion beam line produces metal and inert gas ions and is specially designed to produce up to 2.9 μA of highly collimated ions with single amu mass resolution while precisely controlling the ion’s energy, achieving a ΔE/E∼0.1. Energy resolution can be enhanced further at the expense of flux. Varying the focal length of the final electrostatic lens allows the flux density to be adjusted from 10 to 500 nA/mm2. The beam line has been coupled to an ultra-high-vacuum deposition chamber with a versatile sample manipulator, an electron beam deposition source, residual gas analysis, and real-time reflection high-energy electron diffraction (RHEED). Once prepared, the sample can be moved in situ to perform Auger electron spectroscopy (AES), and scanning tunneling microscopy (STM). The high fluxes with narrow energy distributions this apparatus produces allows the poorly understood hyperthermal energy regime to be probed with RHEED, AES, and STM. The atomic kinetic energy can be varied to measure effects on nuclei densities, growth mode, and surface morphology. STM images of copper films deposited under a variety of conditions illustrate the diverse range of possible results.
Double subtractive spectrometer as a tunable high-resolution broad-bandpass optical filter
Authors: Dunstan D. J. , Frogley M. D.
Published: October 2002

In the optical part of the electromagnetic spectrum, technologies such as dielectric and holographic filters provide a broad-bandpass function with poor resolution between fully blocking and fully transmitting and with almost no tunability. Standard double subtractive spectrometers provide a high-resolution filter function that is tunable over a wide range, but because of the placing of the dispersive element relative to the collimating optics, these instruments are intrinsically narrow-bandpass. A double subtractive spectrometer in which the resolution and tunability are not compromised, yet the bandpass may be as broad as may be desired, can be achieved by placing the dispersive element at twice the focal length from the collimating optics. Such an instrument is described and demonstrated in low-wave-number Raman spectroscopy. With a 0.2 m focal length, it achieves better than 1 cm−1 resolution and can work to 5 cm−1 of the laser line. Throughput is up to 35%, and a bandpass of 1000 cm−1 is demonstrated. Combined with a final stage spectrograph, the laser rejection is 10−13 at 50 cm−1.
Cyclic plasma shearing interferometry for temporal characterization of a laser-produced plasma
Authors: Cobble J. A. , Johnson R. P. , Kurnit N. A. , Montgomery D. S. , Fernández J. C.
Published: October 2002

A cyclic shearing interferometer has been employed to characterize a laser-produced plasma with 180 ps resolution. Counterpropagation maintains an equal path length for the probe and reference beams, and the shear is provided solely by the plasma, which appears within the circuit after the reference beam has passed the laser focal spot. The background is virtually fringe free because of the overlapping of the reference and probe beams so that analysis is simplified. The plasma, which is formed by a line focus, is seen to expand in a cylindrical manner away from the line focus with an exponential density profile. In addition, the interferometer shows evidence of a bow shock when an interaction beam is introduced into the plasma parallel to the direction of the line focus.
Magnetic fluctuation probe design and capacitive pickup rejection
Authors: Franck Christian M. , Grulke Olaf , Klinger Thomas
Published: October 2002

In this article the capacitive pickup of magnetic fluctuation probes for plasma applications is studied. The nine most commonly used probe designs are compared with respect to their capacitive pickup rejection, magnetic sensitivity, and minimum plasma disturbance. For absolute calibration, well defined electric and magnetic field fluctuations are produced separately in a Faraday cup and in a Helmholtz magnetic field coil configuration, respectively. A sample measurement in a radio frequency helicon plasma demonstrates that the optimum probe design is well suited for measuring magnetic fluctuations in a plasma environment.
Spin and energy analysis of electron beams: Coupling a polarimeter based on exchange scattering to a hemispherical analyzer
Authors: Bertacco R. , Marcon M. , Trezzi G. , Duò L. , Ciccacci F.
Published: October 2002

We have coupled a high efficiency polarimeter based on exchange scattering from a magnetized target to a hemispherical analyzer. The target is a Fe(001)-p(1×1)O surface which gives rise to highly spin-dependent scattering in the 4–6 eV electron kinetic energy range. Due to the low scattering energy, the design of the transfer electron optics from the analyzer exit slit to the target is really crucial. We describe in detail the adopted solution along with the performances of the entire apparatus. For low values of the analyzer pass energy we have measured an overall efficiency of 7×10−4 with an analyzing power (Sherman function) of 0.2. As an example of application spin-resolved photoemission data from Fe(001) are reported.