Design of a neutron microscope based on Wolter mirrors.

The predominant geometry for a neutron imaging experiment is that of a pinhole camera. This is primarily due to the difficulty in focusing neutrons due to the weak refractive index, which is also strongly chromatic. Proof of concept experiments demonstrated that neutron image forming lenses based on reflective Wolter mirrors can produce quantitative, high spatial resolution neutron images while also increasing the time resolution compared to the conventional pinhole camera geometry. Motivated by these results, we report the design of a neutron microscope where two Wolter mirrors replace condensing and objective lenses, in direct analogy with typical visible light microscopes. Ray tracing results indicate that this system will yield 3 µm spatial resolution images with an acquisition time of order <1 s (104 faster than currently possible at this spatial resolution) with a field of view of about 5 mm in diameter.

Direct observation of spin rotation in Bragg scattering due to the spin-orbit interaction in silicon.

As a neutron scatters from a target nucleus, there is a small but measurable effect caused by the interaction of the neutron's magnetic dipole moment with that of the partially screened electric field of the nucleus. This spin-orbit interaction is typically referred to as Schwinger scattering and induces a small rotation of the neutron's spin on the order of 10-4 rad for Bragg diffraction from silicon. In our experiment, neutrons undergo greater than 100 successive Bragg reflections from the walls of a slotted, perfect-silicon crystal to amplify the total spin rotation. A magnetic field is employed to insure constructive addition as the neutron undergoes this series of reflections. The strength of the spin-orbit interaction, which is directly proportional to the electric field, was determined by measuring the rotation of the neutron's spin-polarization vector. Our measurements show good agreement with the expected variation of this rotation with the applied magnetic field, while the magnitude of the rotation is ≈40 % larger than expected.

Three Phase-Grating Moiré Neutron Interferometer for Large Interferometer Area Applications.

We demonstrate a three phase-grating moiré neutron interferometer in a highly intense neutron beam as a robust candidate for large area interferometry applications and for the characterization of materials. This novel far-field moiré technique allows for broad wavelength acceptance and relaxed requirements related to fabrication and alignment, thus circumventing the main obstacles associated with perfect crystal neutron interferometry. We observed interference fringes with an interferometer length of 4 m and examined the effects of an aluminum 6061 alloy sample on the coherence of the system. Experiments to measure the autocorrelation length of samples and the universal gravitational constant are proposed and discussed.

Neutron and X-ray Tomography (NeXT) system for simultaneous, dual modality tomography.

Dual mode tomography using neutrons and X-rays offers the potential of improved estimation of the composition of a sample from the complementary interaction of the two probes with the sample. We have developed a simultaneous neutron and 90 keV X-ray tomography system that is well suited to the study of porous media systems such as fuel cells, concrete, unconventional reservoir geologies, limestones, and other geological media. We present the characteristic performance of both the neutron and X-ray modalities. We illustrate the use of the simultaneous acquisition through improved phase identification in a concrete core.

Urinary tract infection after voiding cystourethrogram.

BACKGROUND: Reported rates of post-procedural urinary tract infection (ppUTI) after voiding cystourethrogram (VCUG) are highly variable (0-42%). OBJECTIVE: This study aimed to determine the risk of ppUTI after cystogram, and evaluate predictors of ppUTI. STUDY DESIGN: A retrospective cohort study of children undergoing VCUG or radionuclide cystogram (henceforth 'cystogram') was conducted. Children with neurogenic bladder who underwent cystogram in the operating room and without follow-up at the study institution were excluded. Incidence of symptomatic ppUTI within 7 days after cystogram was recorded. Predictors of ppUTI were evaluated using univariate statistics. RESULTS: A total of 1108 children (54% female, median age 1.1 years) underwent 1203 cystograms: 51% were on periprocedural antibiotics, 75% had a pre-existing urologic diagnosis (i.e., vesicoureteral reflux (VUR) or hydronephrosis; not UTI alone), and 18% had a clinical UTI within 30 days before cystogram. Of the cystograms, 41% had an abnormal cystogram and findings included VUR (82%), ureterocele (6%), and diverticula (6%). Twelve children had a ppUTI (1.0%; four girls, five uncircumcised boys, three circumcised boys; median age 0.9 years). Factors significantly associated with diagnosis of a ppUTI (Summary fig.) included: pre-existing urologic diagnosis prior to cystogram (12/12, 100% of patients with ppUTI), abnormal cystogram results (11/12, 92%), and use of periprocedural antibiotics (11/12, 92%). All 11 children with an abnormal cystogram had VUR ≥ Grade III. However, among all children with VUR ≥ Grade III, 4% (11/254) had a ppUTI. DISCUSSION: This is the largest study to date that has examined incidence and risk factors for ppUTI after cystogram. The retrospective nature of the study limited capture of some clinical details. This study demonstrated that the risk of ppUTI after a cystogram is very low (1.0% in this cohort). Having a pre-existing urologic diagnosis such as VUR or hydronephrosis was associated with ppUTI; therefore, children with moderate or high-grade VUR on cystogram may be at highest risk. Development of ppUTI after cystogram also highlighted the potential for a delay in diagnosis or oversight of a healthcare-associated infection due to several factors: 1) cystograms may be ordered, performed/interpreted, and followed up by multiple different providers; and 2) such infections are not captured by traditional healthcare-associated infection surveillance strategies. CONCLUSIONS: The risk of ppUTI after a cystogram is very low. Only children with pre-existing urologic diagnoses developed ppUTI in this study. This study's findings suggest that children undergoing a cystogram should not be given peri-procedural antibiotic prophylaxis for the sole purpose of ppUTI prevention.

A New Experiment for Investigating Evaporation and Condensation of Cryogenic Propellants.

Passive and active technologies have been used to control propellant boil-off, but the current state of understanding of cryogenic evaporation and condensation in microgravity is insufficient for designing large cryogenic depots critical to the long-term space exploration missions. One of the key factors limiting the ability to design such systems is the uncertainty in the accommodation coefficients (evaporation and condensation), which are inputs for kinetic modeling of phase change. A novel, combined experimental and computational approach is being used to determine the accommodation coefficients for liquid hydrogen and liquid methane. The experimental effort utilizes the Neutron Imaging Facility located at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland to image evaporation and condensation of hydrogenated propellants inside of metallic containers. The computational effort includes numerical solution of a model for phase change in the contact line and thin film regions as well as an CFD effort for determining the appropriate thermal boundary conditions for the numerical solution of the evaporating and condensing liquid. Using all three methods, there is the possibility of extracting the accommodation coefficients from the experimental observations. The experiments are the first known observation of a liquid hydrogen menisci condensing and evaporating inside aluminum and stainless steel cylinders. The experimental technique, complimentary computational thermal model and meniscus shape determination are reported. The computational thermal model has been shown to accurately track the transient thermal response of the test cells. The meniscus shape determination suggests the presence of a finite contact angle, albeit very small, between liquid hydrogen and aluminum oxide.

Average Soil Water Retention Curves Measured by Neutron Radiography.

Water retention curves are essential for understanding the hydrologic behavior of partially saturated porous media and modeling flow and transport processes within the vadose zone. We directly measured the main drying and wetting branches of the average water retention function obtained using two-dimensional neutron radiography. Flint sand columns were saturated with water and then drained and rewetted under quasi-equilibrium conditions using a hanging water column setup. Digital images (2048 by 2048 pixels) of the transmitted flux of neutrons were acquired at each imposed matric potential (∼10-15 matric potential values per experiment) at the National Institute of Standards and Technology Center for Neutron Research BT-2 neutron imaging beam line. Volumetric water contents were calculated on a pixel-by-pixel basis using Beer-Lambert's law after taking into account beam hardening and geometric corrections. To account for silica attenuation and remove scattering effects at high water contents, the volumetric water contents were normalized (to give relative saturations) by dividing the drying and wetting sequences of images by the images obtained at saturation and satiation, respectively. The resulting pixel values were then averaged and combined with information on the imposed basal matric potentials to give average water retention curves. The average relative saturations obtained by neutron radiography showed an approximate one-to-one relationship with the average values measured volumetrically using the hanging water column setup. There were no significant differences (P < 0.05) between the parameters of the van Genuchten equation fitted to the average neutron radiography data and those estimated from replicated hanging water column data. Our results indicate that neutron imaging is a very effective tool for quantifying the average water retention curve.

Accurate measurement of the through-plane water content of proton-exchange membranes using neutron radiography.

The water sorption of proton-exchange membranes (PEMs) was measured in situ using high-resolution neutron imaging in small-scale fuel cell test sections. A detailed characterization of the measurement uncertainties and corrections associated with the technique is presented. An image-processing procedure resolved a previously reported discrepancy between the measured and predicted membrane water content. With high-resolution neutron-imaging detectors, the water distributions across N1140 and N117 Nafion membranes are resolved in vapor-sorption experiments and during fuel cell and hydrogen-pump operation. The measured in situ water content of a restricted membrane at 80 °C is shown to agree with ex situ gravimetric measurements of free-swelling membranes over a water activity range of 0.5 to 1.0 including at liquid equilibration. Schroeder's paradox was verified by in situ water-content measurements which go from a high value at supersaturated or liquid conditions to a lower one with fully saturated vapor. At open circuit and during fuel cell operation, the measured water content indicates that the membrane is operating between the vapor- and liquid-equilibrated states.

Metabolic abnormalities and viral replication are associated with biomarkers of vascular dysfunction in HIV-infected children.

OBJECTIVES: HIV-infected children may be at risk for premature cardiovascular disease. We compared levels of biomarkers of vascular dysfunction in HIV-infected children (with and without hyperlipidaemia) with those in HIV-exposed, uninfected (HEU) children enrolled in the Pediatric HIV/AIDS Cohort Study (PHACS), and determined factors associated with these biomarkers. METHODS: A prospective cohort study was carried out. Biomarkers of inflammation [C-reactive protein (CRP), interleukin-6 (IL-6) and monocyte chemoattractant protein-1 (MCP1)], coagulant dysfunction (fibrinogen and P-selectin), endothelial dysfunction [soluble intracellular cell adhesion molecule-1 (sICAM), soluble vascular cell adhesion molecule-1 (sVCAM) and E-selectin], and metabolic dysfunction (adiponectin) were measured in 226 HIV-infected and 140 HEU children. Anthropometry, body composition, lipids, glucose, insulin, HIV disease severity, and antiretroviral therapy were recorded. RESULTS: The median ages of the children were 12.3 years in the HIV-infected group and 10.1 years in the HEU group. Body mass index (BMI) z-scores, waist and hip circumferences, and percentage body fat were lower in the HIV-infected children. Total and non-high-density lipoprotein (HDL) cholesterol and triglycerides were higher in HIV-infected children. HIV-infected children also had higher MCP-1, fibrinogen, sICAM and sVCAM levels. In multivariable analyses in the HIV-infected children alone, BMI z-score was associated with higher CRP and fibrinogen, but lower MCP-1 and sVCAM. Unfavourable lipid profiles were positively associated with IL-6, MCP-1, fibrinogen, and P- and E-selectin, whereas increased HIV viral load was associated with markers of inflammation (MCP-1 and CRP) and endothelial dysfunction (sICAM and sVCAM). CONCLUSIONS: HIV-infected children have higher levels of biomarkers of vascular dysfunction than do HEU children. Risk factors associated with higher biomarkers include unfavourable lipid levels and active HIV replication.

The Fundamental Neutron Physics Facilities at NIST.

The program in fundamental neutron physics at the National Institute of Standards and Technology (NIST) began nearly two decades ago. The Neutron Interactions and Dosimetry Group currently maintains four neutron beam lines dedicated to studies of fundamental neutron interactions. The neutrons are provided by the NIST Center for Neutron Research, a national user facility for studies that include condensed matter physics, materials science, nuclear chemistry, and biological science. The beam lines for fundamental physics experiments include a high-intensity polychromatic beam, a 0.496 nm monochromatic beam, a 0.89 nm monochromatic beam, and a neutron interferometer and optics facility. This paper discusses some of the parameters of the beam lines along with brief presentations of some of the experiments performed at the facilities.

Thermal and cold neutron phase-contrast radiography.

In this paper, we will discuss a phase-contrast imaging method that avoids the complications of interferometry to provide phase contrast in weakly absorbing samples. A transversely coherent neutron beam is used with the traditional radiography scheme. Images taken with this scheme show dramatic intensity variations due to sharp changes in the neutron wave refractive index. With some numerical processing these images may be used to reconstruct a quantitative phase radiograph of specimens imaged with this technique.

Quantitative phase radiography with polychromatic neutrons.

We develop and experimentally demonstrate a formalism that allows accurate phase imaging using neutron sources producing highly polychromatic beams. The results of measurements from a rectangular block of silicon compare favorably with theoretical simulations based upon the known composition and geometry of the block. The increased flux and reduced exposure times will permit a simple extension of the technique to tomographic phase imaging.

Precision neutron interferometric measurement of the nd coherent neutron scattering length and consequences for models of three-nucleon forces.

We have performed the first high precision measurement of the coherent neutron scattering length of deuterium in a pure sample using neutron interferometry. We find b(nd)=(6.665+/-0.004) fm in agreement with the world average of previous measurements using different techniques, b(nd)=(6.6730+/-0.0045) fm. We compare the new world average for the nd coherent scattering length b(nd)=(6.669+/-0.003) fm to calculations of the doublet and quartet scattering lengths from several modern nucleon-nucleon potential models with three-nucleon force (3NF) additions and show that almost all theories are in serious disagreement with experiment. This comparison is a more stringent test of the models than past comparisons with the less precisely determined doublet scattering length of (2)a(nd)=(0.65+/-0.04) fm.

Changes in lean body mass and total body weight are weakly associated with physical functioning in patients with HIV infection.

CONTEXT: For clinicians managing weight loss in patients with HIV, it would be useful to understand how changes in lean body mass (LBM) effect physical functioning, and whether LBM is more strongly related to physical functioning than total body weight (TBW). OBJECTIVE: To determine the relationship of changes in LBM and changes in total body weight (TBW) to changes in self-reported physical functioning in men and women with HIV infection. METHODS: Study design was longitudinal analysis of 1474 patient-intervals (each interval was approximately 6 months long) in 486 persons. Patients were participants in Nutrition for Healthy Living, a cohort study of HIV positive persons in Massachusetts and Rhode Island. The main outcome measure was change in self-reported physical functioning. RESULTS: Of the 1,474 intervals, 1,165 were contributed by men and 309 by women. The mean CD4 count for the 1,474 intervals was 383 cells/ micro L. In men, 5 kg changes in LBM and TBW were associated with 2.2 (95% confidence interval, 0.9, 3.4, P= 0.001) and 2.6 (95% confidence interval, 1.3, 3.9, P= 0.0002) point changes in physical functioning (on a 100-point scale), respectively, after adjusting for covariates. The relationships of changes in LBM and TBW to changes in physical functioning were linear. In women, there were no significant relationships between changes in LBM or TBW to changes in physical functioning. CONCLUSIONS: In this longitudinal analysis of relatively healthy persons with HIV infection, changes in LBM and TBW were significantly related to changes in physical functioning in men, but the magnitude of the relationship was small. In women, changes in LBM and TBW were not related to changes in physical functioning. Our data suggest that it is not necessary to measure body composition (lean and fat compartments) to understand the impact of changes in weight on physical functioning - it is sufficient to follow total body weight.

Concordance of human papillomavirus in the cervix and urine among inner city adolescents.

OBJECTIVES: To evaluate concordance for human papillomaviruses (HPVs) between cervix and urine in sexually active adolescents. METHODS: Cervical swabs and urine were collected from 80 adolescents in Baltimore, MD. Specimens were tested for 34 HPVs by PCR and for cancer-associated HPVs by Hybrid Capture (HC II) Probe B. Cervical vs. urine prevalence was evaluated by logistic regression with general estimating equations. Risk factors for prevalence and viral burden were evaluated by Fisher's exact and Kruskal-Wallis tests, respectively. RESULTS: HPV prevalence by PCR, for any HPV, was very high in the cervix (90.0%) and somewhat lower in urine (75.0%) (odds ratio, 1.07; 95% confidence interval 1.07 to 1.34). Only one adolescent was HPV-positive in urine alone. Among HPV-PCR positives at either or both sites, concordance was 82% for presence of any HPV and 40% for specific HPV types. Multiple infections were common at both sites. On an average, HC II viral burden (relative light unit ratio) was 9-fold higher in cervix than in urine (median, 47.3 vs. 4.9; P = 0.005) but correlated poorly between the two sites of the same individual (r = 0.14). Compared with normal adolescents, those with squamous intraepithelial lesions had a much higher prevalence of HPV by HC II in cervix (100% vs. 28.6, P<0.0001) as well as in urine (86.7% vs. 35.4%, P = 0.002) and a significantly higher viral burden in the cervix (median, 141.8 vs. 7.3, P = 0.0045) but not in urine (median, 22.7 vs. 4.38; P = 0.13). CONCLUSION: There was a very high prevalence of HPV in cervix and urine of sexually active adolescents. Testing urine for HPV may be useful in epidemiologic investigations and in monitoring of infected women.

Relationship of hormonal contraception and cervical ectopy as measured by computerized planimetry to chlamydial infection in adolescents.

BACKGROUND: Adolescents are at increased risk for chlamydial infection and its sequelae. Hormonal contraception and cervical ectopy were previously suggested risk factors for chlamydia. GOAL: To determine if chlamydia is more prevalent in female participants with greater ectopy and in hormonal contraceptive users. STUDY DESIGN: Ninety-seven adolescent females aged 11 to 20 years were recruited from two Baltimore inner-city clinics. After administering a reproductive history questionnaire, endocervical specimens were tested for Chlamydia trachomatis by polymerase chain reaction. After acetic acid application to the cervix, cervical photographs were taken, the area of ectopy was quantified by computerized planimetry, and ectopy was categorized as none (0mm2), mild (< 22mm2), and moderate (> 22mm2). The likelihood of chlamydia by ectopy and type of hormonal contraceptive use was determined by logistic regression adjusted for age and sexual partners. RESULTS: The odds of chlamydial infection was similar in persons with mild ectopy compared with no ectopy (adjusted odds ratio [OR], 0.76; 95% CI, 0.14-4.03), and in persons with moderate ectopy compared with no ectopy (adjusted OR, 1.94; 95% CI, 0.40-9.39). The likelihood of chlamydia was higher in depot-medroxyprogesterone acetate users compared with nonhormone users (adjusted OR, 5.44; 95% CI, 1.25-23.6). Oral contraceptive users did not have an increased likelihood of chlamydia (adjusted OR, 0.92; 95% CI, 0.10-8.78). CONCLUSION: Using a new, reliable, and standardized technique to quantify cervical ectopy, the authors did not find an elevated prevalence of chlamydial infection in adolescents with cervical ectopy. Depot-medroxyprogesterone acetate use may increase the risk of chlamydial infection compared with combined estrogen-progestin oral contraceptives.

Histologic development of cervical ectopy: relationship to reproductive hormones.

BACKGROUND AND OBJECTIVES: Cervical ectopy has been proposed as a risk factor for chlamydial infection, HIV, and other sexually transmitted diseases (STDs). Ectopy is a histologic phenomenon resulting from a complex interplay of morphologic and hormonal processes. Reproductive hormones influence the production of ectopy during late fetal life, puberty, pregnancy, and with use of oral contraceptives. Ectopy is modified over time by squamous metaplasia and epitheliazation, low pH, trauma, and possibly by cervical infection. STUDY DESIGN: The authors review the histologic development of ectopy from late fetal life to menopause to understand STD risk. RESULTS: Ectopy is often assessed and quantified by direct, unaided observation during speculum examinations. This method may result in inaccurate estimates and misclassification with the transformation zone. CONCLUSION: Valid, reproducible measures of ectopy are necessary for epidemiologic studies to examine the impact of exogenous hormonal contraceptives on the development of ectopy and on potential infection risk.

Ioffe et Al. Reply:.

A Reply to the Comment by C. A. Chatzidimitriou-Dreismann et al.

Cervical ectopy and the transformation zone measured by computerized planimetry in adolescents.

OBJECTIVE: To determine whether cervical ectopy and the transformation (T) zone were larger in adolescents using oral contraceptives (OCs) compared to depot medroxyprogesterone acetate (DMPA). METHOD: Cervical photographs were taken on 91 adolescents in Baltimore, Maryland. Ectopy and T zone size were measured using computerized planimetry. Patients provided reproductive and sexual history. Correlates of ectopy and T zone size were identified by proportional odds and linear regression models, respectively. RESULT: Twenty-five women had no ectopy. Parity was independently associated with greater ectopy (OR 3.9, 95% CI 1.37-11.11). Predictors of smaller ectopy were douching (OR 0.23, 95% CI 0.09-0.65), and shorter sexual history (OR 0.20, 95% CI 0.05-0.74). Neither OC or DMPA were associated with ectopy. Predictors of greater T zone size were years since menarche (13.8 mm2/year, P = 0.003) and OCs (54.7 mm2, P = 0.05). DMPA predicted a smaller T zone (-67.0 mm2, P = 0.01). CONCLUSION: Computerized planimetry provides standardized measurements. Douching and sexual activity may decrease ectopy through increased squamous metaplasia. Hormonal contraceptives were not associated with ectopy in adolescents. However, long-term progestin use may decrease T zone size.