bluuebunny/crossref_metadata_2025 huggingface dataset:
Individual differences in the cortisol and salivary α‐amylase awakening responses in early childhood: Relations to age, sex, and sleep
Authors: Bright Melissa A. , Frick Janet E. , Out Dorothee , Granger Douglas A.
Published: March 2014

Recent studies have examined post‐waking changes in cortisol as a marker of HPA functioning, but questions remain about the stability of this response, as well as its relation to sleep and other ANS markers. The purposes of this study were to a) examine the presence and developmental changes in the cortisol awakening response (CAR) and salivary α‐amylase awakening (sAA‐AR) in a toddler sample and b) determine whether and how sleep relates to these responses in this age group. We measured cortisol and sAA upon awakening (and 30 min post‐waking) and sleep characteristics using actigraphy (e.g., total sleep time, sleep efficiency, number of awakenings) in toddlers (N = 47; 36% female, ages 12–24 months). Forty‐six percent of toddlers demonstrated a CAR and 52% demonstrated a sAA‐AR. Strength of either response did not change linearly with age. Additionally, likelihood of demonstrating the CAR and sAA‐AR was unrelated to age, sex, awakening time, time between samples, and time since feeding. Higher waking cortisol levels were associated with a shorter total sleep time and an earlier awakening. No associations were observed between sleep characteristics and the sAA‐AR,ps > .05. Our findings suggest that these awakening responses function independently of sleep in toddlers. Additionally, the lack of change in percentage of children showing a CAR or sAA‐AR across these ages suggests that these responses are stable and not emerging reliably across the second year of life. © 2014 Wiley Periodicals, Inc. Dev Psychobiol 56: 1300–1315, 2014.
Development and predictive effects of eating disorder risk factors during adolescence: Implications for prevention efforts
Authors: Rohde Paul , Stice Eric , Marti C. Nathan
Published: March 2014

Objective

Although several prospective studies have identified factors that increase risk for eating disorders, little is known about when these risk factors emerge and escalate, or when they begin to predict future eating disorder onset. The objective of this report was to address these key research gaps.

Method

Data were examined from a prospective study of 496 community female adolescents (M = 13.5, SD = 0.7 at baseline) who completed eight annual assessments of potential risk factors and eating disorders from preadolescence to young adulthood.

Results

Three variables exhibited positive linear increases: Perceived pressure to be thin, thin‐ideal internalization, and body dissatisfaction; three were best characterized as quadratic effects: dieting (essentially little change); negative affectivity (overall decrease), and BMI (overall increase). Elevated body dissatisfaction at ages 13, 14, 15, and 16 predicted DSM‐5 eating disorders onset in the 4‐year period after each assessment, but the predictive effects of other risk factors were largely confined to age 14; BMI did not predict eating disorders at any age.

Discussion

The results imply that these risk factors are present by early adolescence, although eating disorders tend to emerge in late adolescence and early adulthood. These findings emphasize the need for efficacious eating disorder prevention programs for early adolescent girls, perhaps targeting 14‐year olds, when risk factors seem to be most predictive. In early adolescence, it might be fruitful to target girls with body dissatisfaction, as this was the most consistent predictor of early eating disorder onset in this study. © 2014 Wiley Periodicals, Inc. (Int J Eat Disord 2015; 48:187–198)
Heteroleptic Group 2 Metal Precursors for Metal Oxide Thin Films
Authors: George Sheby Mary , Park Bo Keun , Kim Chang Gyoun , Chung Taek‐Mo
Published: March 2014

A new class of heteroleptic complexes of calcium, strontium, and barium have been synthesized using 1‐{[2‐(dimethylamino)ethyl](methyl)amino}‐2‐methylpropan‐2‐ol (demampH) and 2,2,6,6‐tetramethyl‐3,5‐heptanedione (tmhdH). Complexes [{Ca(demamp)(tmhd)}2] (4), [{Sr(demamp)(tmhd)}2] (5), and [{Ba(demamp)(tmhd)}3] (6) were prepared in two‐step processes. Partially substituted complexes [{Ca(demamp)(btsa)}2] (1), [{Sr(demamp)(btsa)}2] (2), and [{Ba(demamp)(btsa)}2] (3) [btsa = bis(trimethylsilyl)amide] were isolated and characterized. The molecular structures of all the compounds were studied by single‐crystal X‐ray crystallography. The strontium and calcium complexes have dimeric configuration with bridging of two alkoxide oxygen atoms between the metals, whereas the barium complex is a trimer. Complexes 4 and 5 show higher volatility and thermal stability with respect to the homoleptic compounds, while barium complex 6 is unstable. The TG analyses of compounds 4 and 5 display one‐step curves with 9.0 and 9.6 % residue at 375 and 370 °C, respectively.
Copper‐ and Palladium‐Cocatalyzed Intramolecular C–H Functionalization/C–N Bond Formation: A Route to the Synthesis of Indoloisoquinoline Derivatives
Authors: Hazra Somjit , Mondal Biplab , Rahaman Habibur , Roy Brindaban
Published: March 2014

A Cu and Pd bi‐catalytic system is found to be very effective for the indole C2–H functionalization/C–N bond formation process.This is a unique reaction in which isoquinoline systems were synthesized from aldoximes rather than from ketoximes. During the reaction Cu(OTf)2 converts the aldoximes into the corresponding cyanides and indoloisoquinolines, but introduction of Pd(OAc)2 changes the outcome of the reaction significantly, by suppressing the formation of cyano products, thus giving exclusively indoloisoquinolines. A range of substituted indoloisoquinolines and aza‐indoloisoquinolines are prepared in good to very good yields under air.
Reliability of estimated glomerular filtration rate in patients treated with platinum containing therapy
Authors: Lauritsen Jakob , Gundgaard Maria G. , Mortensen Mette S. , Oturai Peter S. , Feldt‐Rasmussen Bo , Daugaard Gedske
Published: March 2014

Estimates of glomerular filtration rate (eGFR) are widely used when administering nephrotoxic chemotherapy. No studies performed in oncology patients have shown whether eGFR can safely substitute a measured GFR (mGFR) based on a marker method. We aimed to assess the validity of four major formulas based on PCr (Cockcroft‐Gault, MDRD, Wright and CKD‐EPI) in comparison to mGFR in an oncology setting. Patients included had disseminated germ cell cancer and received conventional chemotherapy: bleomycin, etoposide and cisplatin. The mGFR of the patients was compared to all estimates with focus on bias (median percentage error), precision (median absolute percentage error) and accuracy (p10 and p30). The precision of carboplatin dosage based on eGFR was calculated. Data on mGFR, eGFR, and PCr were available in 390 patients, with a total of ∼1,600 measurements. Median PCr and mGFR synchronically decreased after chemotherapy, yielding high bias and low precision of most estimates. Post‐chemotherapy, bias ranged from −0.2% (MDRD after four cycles) to 33.8% (CKD‐EPI after five cycles+), precision ranged from 11.6% (MDRD after four cycles) to 33.8% (CKD‐EPI after five cycles+) and accuracy (p30) ranged from 37.5% (CKD‐EPI after five cycles+) to 86.9% (MDRD after four cycles). Although MDRD appeared acceptable after chemotherapy because of high accuracy, this equation underestimated GFR in all other measurements. Before and years after treatment, Cockcroft‐Gault and Wright offered best results. Precision of carboplatin dosage was low. In conclusion, bias, precision and accuracy were unacceptable in all equations due to a synchronous decrease of PCr and mGFR during chemotherapy.
Iterative projection onto convex sets for quantitative susceptibility mapping
Authors: Deng Weiran , Boada Fernando , Poser Benedikt A. , Schirda Claudiu , Stenger Victor Andrew
Published: March 2014

Purpose

Quantitative susceptibility map (QSM) reconstruction is ill posed due to the zero values on the “magic angle cone” that make the maps prone to streaking artifacts. We propose projection onto convex sets (POCS) in the method of steepest descent (SD) for QSM reconstruction.

Methods

Two convex projections, an object‐support projection in the image domain and a projection in k‐space were used. QSM reconstruction using the proposed SD‐POCS method was compared with SD and POCS alone as well as with truncated k‐space division (TKD) for numerically simulated and 7 Tesla (T) human brain phase data.

Results

The QSM reconstruction error from noise‐free simulated phase data using SD‐POCS is at least two orders of magnitude lower than using SD, POCS, or TKD and has reduced streaking artifacts. Using the l1‐TV reconstructed susceptibility as a gold standard for 7T in vivo imaging, SD‐POCS showed better image quality comparing to SD, POCS, or TKD from visual inspection.

Conclusion

POCS is an alternative method for regularization that can be used in an iterative minimization method such as SD for QSM reconstruction. Magn Reson Med 73:697–703, 2015. © 2014 Wiley Periodicals, Inc.
Bone mineral density among long‐term survivors of childhood acute lymphoblastic leukemia: Results from the St. Jude Lifetime Cohort Study
Authors: Gurney J. G. , Kaste S. C. , Liu W. , Srivastava D. K. , Chemaitilly W. , Ness K. K. , Lanctot J. Q. , Ojha R. P. , Nottage K. A. , Wilson C. L. , Li Z. , Robison L. L. , Hudson M. M.
Published: March 2014

Background

The prevalence of low bone mineral density (BMD) in adult survivors of childhood acute lymphoblastic leukemia (ALL), and the degree of recovery or decline, are not well elucidated.

Procedure

Study subjects (age ≥ 18 years and ≥10 years post‐diagnosis) participated in an institutional follow‐up protocol and risk‐based clinical evaluation based on Children's Oncology Group guidelines. Trabecular volumetric BMD was ascertained using quantitative computed tomography, reported as age‐ and sex‐specific Z‐scores.

Results

At median age 31 years, 5.7% of 845 subjects had a BMD Z‐score of ≤−2 and 23.8% had a Z‐score of −1 to −2. Cranial radiation dose of ≥24 Gy, but not cumulative methotrexate or prednisone equivalence doses, was associated with a twofold elevated risk of a BMD Z‐score of ≤−1. The cranial radiation effect was stronger in females than in males. In a subset of 400 subjects, 67% of those who previously had a BMD Z‐score of ≤−2 improved by one or more categories a median of 8.5 years later.

Conclusions

Very low BMD was relatively uncommon in this sample of adult survivors of childhood ALL, and BMD Z‐scores tended to improve from adolescence to young adulthood. High‐dose cranial or craniospinal radiation exposure was the primary predictor of suboptimal BMD in our study. Given that cranial radiation treatment for childhood ALL is used far more sparingly now than in earlier treatment eras, concerns about persistently low BMD among most current childhood ALL patients may be unwarranted. Pediatr Blood Cancer 2014;61:1270–1276. © 2014 Wiley Periodicals, Inc.
Effects of measuring nestling condition on nest success in the dickcissel (Spiza americana)
Authors: Monroe Adrian P. , Martin James A. , Riffell Samuel K. , Burger L. Wes
Published: March 2014

Handling songbird nestlings is often necessary to investigate a variety of basic and applied research questions, but this may also introduce observer effects that could compromise indices of reproductive success. To test for potential observer effects while measuring nestling condition in a study population of dickcissels (Spiza americana), we handled nestlings from 18 of 30 nests in Prairie, Mississippi, USA. We used generalized linear mixed models to compare nest success rate with nests that were monitored but where nestlings were not handled. Confidence intervals for nest success rates overlapped broadly for nests with handled (0.84, 95% CI = 0.57–0.95) and unhandled nestlings (0.77, 95% CI = 0.44–0.93), and a likelihood ratio test indicated the effect of treatment did not approximate the data better than a null model. We also did not find evidence of adults rejecting or abandoning handled and banded nestlings. This suggests that it is unlikely we incurred negative impacts on nest success when measuring nestling condition in our study. © 2014 The Wildlife Society.
Laparoscopic radiofrequency volumetric thermal ablation of fibroids versus laparoscopic myomectomy
Authors: Brucker Sara Y. , Hahn Markus , Kraemer Dorit , Taran Florin Andrei , Isaacson Keith B. , Krämer Bernhard
Published: March 2014

Objective

To compare the mean hospital discharge times and perioperative outcomes for radiofrequency volumetric thermal ablation (RFVTA) of fibroids and laparoscopic myomectomy (LM).

Methods

The present postmarket, randomized, prospective, single‐center, longitudinal, comparative study, conducted in Tübingen, Germany, evaluated the outcomes of RFVTA and the current standard of care (LM) for symptomatic uterine fibroids in women who desired uterine conservation. The surgeons were blinded to the treatment until all fibroids had been mapped by laparoscopic ultrasound.

Results

The mean hospitalization times were 10.0 ± 5.5 (median 7.8 [range 4.2–25.5]) hours for the RFVTA group and 29.9 ± 14.2 (median 22.6 [range 16.1–68.1]) hours for the LM group (P < 0.001, Wilcoxon test). Intraoperative blood loss was 16 ± 9 (median 20 [range: 0–30]) mL for the RFVTA procedures and 51 ± 57 (median 35 [range 10–300]) mL for the LM procedures. The percentage of fibroids imaged by laparoscopic ultrasound that were treated/excised was 98.6% for RFVTA and 80.3% for LM. Two complications were reported: vertigo (n = 1; RFVTA) and port site hematoma (n = 1; LM).

Conclusion

Radiofrequency volumetric thermal ablation resulted in the treatment of more fibroids, a significantly shorter hospital stay, and less intraoperative blood loss than laparoscopic myomectomy.

ClinicalTrials.gov: NCT01750008
Hydrosonographic assessment of the effects of 2 different suturing techniques on healing of the uterine scar after cesarean delivery
Authors: Sevket Osman , Ates Seda , Molla Taner , Ozkal Fulya , Uysal Omer , Dansuk Ramazan
Published: March 2014

Objective

To compare the effects of 2 suturing techniques (single versus double layer) on healing of the uterine scar after a cesarean delivery.

Methods

In the present randomized, prospective study, 36 women with a term pregnancy who had an elective cesarean delivery were randomly assigned to closure of the uterine incision with a single‐layer locked suture or with a double‐layer locked/unlocked suture. Six months after the operation, the integrity of the cesarean scar at the uterine incision site was assessed by hydrosonography. The healing ratio and the thickness of the residual myometrium covering the defect were calculated as markers of uterine scar healing.

Results

There were no significant differences between the groups in terms of estimated blood loss, operation time, or additional hemostatic suture. However, the mean thickness of the residual myometrium covering the defect was 9.95 ± 1.94 mm after a double‐layer closure and 7.53 ± 2.54 mm after a single‐layer closure (P= 0.005). The mean healing ratio was significantly higher after a double‐layer closure (0.83 ± 0.10) than after a single‐layer closure (0.67 ± 0.15;P= 0.004).

Conclusion

A double‐layer locked/unlocked closure of the uterine incision at cesarean delivery decreases the risk of poor uterine scar healing.
Aβ and cognitive change: Examining the preclinical and prodromal stages of Alzheimer's disease
Authors: Lim Yen Ying , Maruff Paul , Pietrzak Robert H. , Ellis Kathryn A. , Darby David , Ames David , Harrington Karra , Martins Ralph N. , Masters Colin L. , Szoeke Cassandra , Savage Greg , Villemagne Victor L. , Rowe Christopher C. ,   AIBL Research Group
Published: March 2014

Background

High β‐amyloid (Aβ) is associated with faster memory decline in healthy individuals and adults with mild cognitive impairment (MCI). However, longer prospective studies are required to determine if Aβ‐related memory decline continues and whether it is associated with increased rate of disease progression.

Methods

Healthy controls (HCs; n = 177) and adults with MCI (n = 48) underwent neuroimaging for Aβ and cognitive assessment at baseline. Cognition was reassessed 18 and 36 months later.

Results

Compared with low‐Aβ HCs, high‐Aβ HC and MCI groups showed moderate decline in episodic and working memory over 36 months. Those with MCI with low Aβ did not show any cognitive decline. Rates of disease progression were increased in the high‐Aβ HC and MCI groups.

Conclusions

In healthy individuals, high Aβ likely indicates that Alzheimer's disease (AD)‐related neurodegeneration has begun. Once commenced, the rate of decline in cognitive function remains constant across the preclinical and prodromal stages of AD.
Cardiac resynchronization therapy for exercise‐induced left ventricular dysfunction in the setting of left bundle branch block: A case report and review of the literature
Authors: Abraham JoEllyn M. , Thomas James D. , Wilkoff Bruce L.
Published: March 2014

Exercise‐induced dyspnea is one of the most common symptoms that cause a patient to see a physician and a broad differential diagnosis is required. In this case report, we describe a patient with this complaint who had a left bundle branch block and preserved left ventricular function at rest. On stress echocardiography, she had significant exercise‐induced left ventricular dysfunction and associated mitral regurgitation but a coronary angiogram demonstrated normal coronary arteries. Both of the echocardiographic findings, as well as her symptoms, improved with the placement of a bi‐ventricular pacemaker. A brief review of the literature on cardiac resynchronization therapy for indications beyond the current guidelines is also provided.
Measuring and Reasoning
Authors: Bookstein Fred L.
Published: March 2014

In Measuring and Reasoning, Fred L. Bookstein examines the way ordinary arithmetic and numerical patterns are translated into scientific understanding, showing how the process relies on two carefully managed forms of argument:
• Abduction: the generation of new hypotheses to accord with findings that were surprising on previous hypotheses, and
• Consilience: the confirmation of numerical pattern claims by analogous findings at other levels of measurement.
These profound principles include an understanding of the role of arithmetic and, more importantly, of how numerical patterns found in one study can relate to numbers found in others. More than 200 figures and diagrams illuminate the text. The book can be read with profit by any student of the empirical nature or social sciences and by anyone concerned with how scientists persuade those of us who are not scientists why we should credit the most important claims about scientific facts or theories.
Fast track to nanomaterials: microwave assisted synthesis in ionic liquid media
Authors: Kessler Michael T. , Hentschel Maria K. , Heinrichs Christina , Roitsch Stefan , Prechtl Martin H. G.
Published: March 2014

Herein we present a general approach to metal and metal oxide nanoparticles using simple metal salts as starting materials.
The ligation of aspirin to cisplatin demonstrates significant synergistic effects on tumor cells
Authors: Cheng Qinqin , Shi Hongdong , Wang Hongxia , Min Yuanzeng , Wang Jun , Liu Yangzhong
Published: March 2014

Asplatin, a fusion of aspirin and cisplatin, exhibits significant synergistic-effects on tumor cells and cisplatin-resistant cells.
A bio-inspired inner-motile photocatalyst film: a magnetically actuated artificial cilia photocatalyst
Authors: Zhang Dunpu , Wang Wei , Peng Fengping , Kou Jiahui , Ni Yaru , Lu Chunhua , Xu Zhongzi
Published: March 2014

An inner-motile photocatalyst film is developed by employing artificial cilia, which provides an impactful methodology for overcoming mass transfer limitation due to the microfluidic mixing capability. The photocatalytic performance is significantly enhanced.
Self-assembled conjugated polymer/carboxymethyl chitosan grafted poly(p-dioxanone) nanomicelles and their use in functionalized indicator paper for fast and visual detection of a banned food dye
Authors: Chen Hui , Chen Meiwan , Wang Xiaohui , Sun Runcang
Published: March 2014

Fluorescent nanoparticles composed of a self-assembled polysaccharide derivative and a conjugated polymer show greatly improved sensitivity for the selective detection of a banned food dye in aqueous media.
Paper substrate modification for rapid capillary flow in microfluidic paper-based analytical devices
Authors: Xu Y. , Enomae T.
Published: March 2014

The development of microfluidic paper-based analytical devices is the most promising emerging research globally, due to its main advantage of spontaneous liquid transport.
Zirconium–Beta zeolite as a robust catalyst for the transformation of levulinic acid to γ-valerolactone via Meerwein–Ponndorf–Verley reduction
Authors: Wang Jie , Jaenicke Stephan , Chuah Gaik-Khuan
Published: March 2014

Zr–Beta zeolite is a robust and active catalyst for the Meerwein–Ponndorf–Verley reduction of levulinic acid to γ-valerolactone, a versatile intermediate for bio-fuels and chemicals.
Practical polar code construction using generalised generator matrices
Authors: Serbetci Berksan , Pusane Ali Emre
Published: March 2014

Polar coding is a recently proposed coding technique that can provably achieve the channel capacity. The polar code structure, which is based on the original 2 × 2 generator matrix, polarises the channels, that is, a portion of the channel capacities approach 1, whereas the remaining channel capacities approach 0. Owing to the specific size of this original generator matrix, polar codes can only have code lengths equal to the powers of 2, resulting in inefficiency for codes of practical lengths. In this study, the performance of finite‐length polar codes over the binary erasure channel is analysed. A normalised polarisation distance measure is defined and polar codes from different generator matrices showing different amount of polarisation are compared using this measure. Encoding structures for these generalised polar codes are proposed and polarisation performances in both asymptotical and finite‐length cases are investigated for generator matrices of size 3 × 3 and 4 × 4. A generalised decoder is also proposed for this generator matrix and its erasure rate is compared with that of the original generator matrix. It is shown that polar codes that have performance similar to the original construction can be constructed and used for a variety of code lengths, not necessarily equal to powers of 2, using generalised generator matrices.
Controller design with model identification approach in wide area power system
Authors: Kishor Nand , Haarla Liisa , Turunen Jukka , Larsson Mats , Mohanty Soumya R.
Published: March 2014

Using wide area monitoring systems (WAMS) offers a possibility for an integrated measurement‐based and model‐based control, which suits to the operation of large electric power system (EPS), along with online analysis. This study presents studies on fixed‐order controller design through model identification approach with use of synchronous measurement data. Firstly, in the study, the coherent generator in each area of large EPS is determined by the mutual information theory. Then, state‐space two‐input two‐output model is identified for the generator that has highest participation factor and thus referred as coherent generator. The model identification algorithms; least‐square, instrumental variable and subspace state‐space based generalised Poisson moment function are used. Next, WAMS level model is identified between the input controllable variable and speed deviation difference of coherent generator of each area. Finally, a local controller (decentralised) in each coherent area and a centralised controller at WAMS level between two coherent areas are designed by optimisation of the several design functions; H∞ norm, H2 norm, spectral abscissa and complex stability radius, as much as possible. These controllers feed supplementary control signal in addition to one fed by local conventionally tuned power system stabiliser. The centralised controller at WAMS level is demonstrated to stabilise the speed deviations of each generator between any two areas in the large EPS. The study is investigated with different input signal variables; ΔVref, ΔPm excited by different pattern of disturbances.
Photovoltaic power forecasting using statistical methods: impact of weather data
Authors: De Giorgi Maria Grazia , Congedo Paolo Maria , Malvoni Maria
Published: March 2014

An important issue for the growth and management of grid‐connected photovoltaic (PV) systems is the possibility to forecast the power output over different horizons. In this work, statistical methods based on multiregression analysis and the Elmann artificial neural network (ANN) have been developed in order to predict power production of a 960 kWP grid‐connected PV plant installed in Italy. Different combinations of the time series of produced PV power and measured meteorological variables were used as inputs of the ANN. Several statistical error measures are evaluated to estimate the accuracy of the forecasting methods. A decomposition of the standard deviation error has been carried out to identify the amplitude and phase error. The skewness and kurtosis parameters allow a detailed analysis of the distribution error.
Optical and Magentic Properties of Trivalent Vanadium Complexes
Authors: MacFarlane R. M.
Published: March 2014

An analysis of the optical and magnetic properties of trivalent vanadium complexes is given on the basis of the ligand-field model. The calculation of g values and magnetic susceptibility is outlined, using eigenstates of the "zero magnetic field" Hamiltonian, including trigonal field and spin-orbit terms. This enables the results of magnetic resonance experiments to be interpreted without the use of a spin Hamiltonian, in cases where the optical spectrum has been measured. The example of vanadium corundum is discussed in some detail. The dependence of energy levels on the parameters B, C, Δ, v, v′, and ζ is used to determine these parameters from the absorption spectrum. Values of the magnetic constants of vanadium corundum are obtained as g∥= 1.919, g⊥= 1.719, and D=7.9 cm-1, in excellent agreement with previous experimental results. The paramagnetic susceptibility is predicted in the range lo-300°K.
Ionization dynamics and radiative behavior of a betatron driven gold atom
Authors: Davis J. , Petrova Tz. B. , Whitney K. G.
Published: March 2014

The study of inner-shell transitions induced by an intense (>1019 W/cm2) ultrashort (∼5 fs) x-ray pulse provides a challenging opportunity to investigate the behavior and dynamics of hollow atoms and to explore the feasibility of creating population inversions in some of the inner-shell states that may lead to a variety of amplifications and gains in the x-ray regime. In this paper, we investigate the interaction through inner-shell photoionizations of a spectrally broad femtosecond pulse of betatron x-ray radiation incident on a gold atom. The level populations of Pt-like Au and Ir-like Au are described by non-(local thermodynamic equilibrium) inner-shell dynamics and compared and contrasted with the level populations created by a "single" frequency x-ray laser pulse. Gain coefficients for a variety of transitions are calculated. It is found that long wavelength x-rays must be filtered from the betatron spectrum before any population inversions can be generated.
Radiation from mixed multi-planar wire arrays
Authors: Safronova A. S. , Kantsyrev V. L. , Esaulov A. A. , Chuvatin A. S. , Weller M. E. , Shlyaptseva V. V. , Shrestha I. , Keim S. F. , Stafford A. , Coverdale C. A. , Apruzese J. P. , Ouart N. D. , Giuliani J. L.
Published: March 2014

The study of radiation from different wire materials in wire array Z-pinch plasma is a very challenging topic because it is almost impossible to separate different plasmas at the stagnation. A new approach is suggested based on planar wire array (PWA) loads to assess this problem. Multi-planar wire arrays are implemented that consist of few planes, each with the same number of wires and masses but from different wire materials, arranged in parallel rows. In particular, the experimental results obtained with triple PWAs (TPWAs) on the UNR Zebra generator are analyzed with Wire Ablation Dynamics Model, non-local thermodynamic equilibrium kinetic model, and 2D radiation magneto-hydrodynamic to illustrate this new approach. In TPWAs, two wire planes were from mid-atomic-number wire material and another plane was from alloyed Al, placed either in the middle or at the edge of the TPWA. Spatial and temporal properties of K-shell Al and L-shell Cu radiations were analyzed and compared from these two configurations of TPWAs. Advantages of the new approach are demonstrated and future work is discussed.
Resolving microstructures in Z pinches with intensity interferometry
Authors: Apruzese J. P. , Kroupp E. , Maron Y. , Giuliani J. L. , Thornhill J. W.
Published: March 2014

Nearly 60 years ago, Hanbury Brown and Twiss [R. Hanbury Brown and R. Q. Twiss, Nature 178, 1046 (1956)] succeeded in measuring the 30 nrad angular diameter of Sirius using a new type of interferometry that exploited the interference of photons independently emitted from different regions of the stellar disk. Its basis was the measurement of intensity correlations as a function of detector spacing, with no beam splitting or preservation of phase information needed. Applied to Z pinches, X pinches, or laser-produced plasmas, this method could potentially provide spatial resolution under one micron. A quantitative analysis based on the work of Purcell [E. M. Purcell, Nature 178, 1449 (1956)] reveals that obtaining adequate statistics from x-ray interferometry of a Z-pinch microstructure would require using the highest-current generators available. However, using visible light interferometry would reduce the needed photon count and could enable its use on sub-MA machines.
Effective versus ion thermal temperatures in the Weizmann Ne Z-pinch: Modeling and stagnation physics
Authors: Giuliani J. L. , Thornhill J. W. , Kroupp E. , Osin D. , Maron Y. , Dasgupta A. , Apruzese J. P. , Velikovich A. L. , Chong Y. K. , Starobinets A. , Fisher V. , Zarnitsky Yu. , Bernshtam V. , Fisher A. , Mehlhorn T. A. , Deeney C.
Published: March 2014

The difference between the ion thermal and effective temperatures is investigated through simulations of the Ne gas puff z-pinch reported by Kroupp et al. [Phys. Rev. Lett. 107, 105001 (2011)]. Calculations are performed using a 2D, radiation-magnetohydrodynamic code with Tabular Collisional-Radiative Equilibrium, namely Mach2-TCRE [Thornhill et al., Phys. Plasmas 8, 3480 (2001)]. The extensive data set of imaging and K-shell spectroscopy from the experiments provides a challenging validation test for z-pinch simulations. Synthetic visible images of the implosion phase match the observed large scale structure if the breakdown occurs at the density corresponding to the Paschen minimum. At the beginning of stagnation (−4 ns), computed plasma conditions change rapidly showing a rising electron density and a peak in the ion thermal temperature of ∼1.8 keV. This is larger than the ion thermal temperature (<400 eV) inferred from the experiment. By the time of peak K-shell power (0 ns), the calculated electron density is similar to the data and the electron and ion thermal temperatures are equilibrated, as is observed. Effective ion temperatures are obtained from calculated emission line widths accounting for thermal broadening and Doppler velocity shifts. The observed, large effective ion temperatures (∼4 keV) early in the stagnation of this Ne pinch can be explained solely as a combination of compressional ion heating and steep radial velocity gradients near the axis. Approximations in the modeling are discussed in regard to the higher ion thermal temperature and lower electron density early in the stagnation compared to the experimental results.
Detailed analysis of hollow ions spectra from dense matter pumped by X-ray emission of relativistic laser plasma
Authors: Hansen S. B. , Colgan J. , Faenov A. Ya. , Abdallah J. , Pikuz S. A. , Skobelev I. Yu. , Wagenaars E. , Booth N. , Culfa O. , Dance R. J. , Tallents G. J. , Evans R. G. , Gray R. J. , Kaempfer T. , Lancaster K. L. , McKenna P. , Rossall A. K. , Schulze K. S. , Uschmann I. , Zhidkov A. G. , Woolsey N. C.
Published: March 2014

X-ray emission from hollow ions offers new diagnostic opportunities for dense, strongly coupled plasma. We present extended modeling of the x-ray emission spectrum reported by Colgan et al. [Phys. Rev. Lett. 110, 125001 (2013)] based on two collisional-radiative codes: the hybrid-structure Spectroscopic Collisional-Radiative Atomic Model (SCRAM) and the mixed-unresolved transition arrays (MUTA) ATOMIC model. We show that both accuracy and completeness in the modeled energy level structure are critical for reliable diagnostics, investigate how emission changes with different treatments of ionization potential depression, and discuss two approaches to handling the extensive structure required for hollow-ion models with many multiply excited configurations.
Radiation sources with planar wire arrays and planar foils for inertial confinement fusion and high energy density physics research
Authors: Kantsyrev V. L. , Chuvatin A. S. , Safronova A. S. , Rudakov L. I. , Esaulov A. A. , Velikovich A. L. , Shrestha I. , Astanovitsky A. , Osborne G. C. , Shlyaptseva V. V. , Weller M. E. , Keim S. , Stafford A. , Cooper M.
Published: March 2014

This article reports on the joint success of two independent lines of research, each of them being a multi-year international effort. One of these is the development of innovative sources, such as planar wire arrays (PWAs). PWAs turned out to be a prolific radiator, which act mainly as a resistor, even though the physical mechanism of efficient magnetic energy conversion into radiation still remains unclear. We review the results of our extensive studies of PWAs. We also report the new results of the experimental comparison PWAs with planar foil liners (another promising alternative to wire array loads at multi-mega-ampere generators). Pioneered at UNR, the PWA Z-pinch loads have later been tested at the Sandia National Laboratories (SNL) on the Saturn generator, on GIT-12 machine in Russia, and on the QiangGuang-1 generator in China, always successfully. Another of these is the drastic improvement in energy efficiency of pulsed-power systems, which started in early 1980s with Zucker's experiments at Naval Research Laboratory (NRL). Successful continuation of this approach was the Load Current Multiplier (LCM) proposed by Chuvatin in collaboration with Rudakov and Weber from NRL. The 100 ns LCM was integrated into the Zebra generator, which almost doubled the plasma load current, from 0.9 to 1.7 MA. The two above-mentioned innovative approaches were used in combination to produce a new compact hohlraum radiation source for ICF, as jointly proposed by SNL and UNR [Jones et al., Phys. Rev. Lett. 104, 125001 (2010)]. The first successful proof-of-the-principle experimental implementation of new hohlraum concept at university-scale generator Zebra/LCM is demonstrated. A numerical simulation capability with VisRaD code (from PRISM Co.) established at UNR allowed for the study of hohlraum coupling physics and provides the possibility of optimization of a new hohlraum. Future studies are discussed.
Radiation from Ag high energy density Z-pinch plasmas and applications to lasing
Authors: Weller M. E. , Safronova A. S. , Kantsyrev V. L. , Esaulov A. A. , Shrestha I. , Apruzese J. P. , Giuliani J. L. , Chuvatin A. S. , Stafford A. , Keim S. F. , Shlyaptseva V. V. , Osborne G. C. , Petkov E. E.
Published: March 2014

Silver (Ag) wire arrays were recently introduced as efficient x-ray radiators and have been shown to create L-shell plasmas that have the highest electron temperature (>1.8 keV) observed on the Zebra generator so far and upwards of 30 kJ of energy output. In this paper, results of single planar wire arrays and double planar wire arrays of Ag and mixed Ag and Al that were tested on the UNR Zebra generator are presented and compared. To further understand how L-shell Ag plasma evolves in time, a time-gated x-ray spectrometer was designed and fielded, which has a spectral range of approximately 3.5–5.0 Å. With this, L-shell Ag as well as cold Lα and Lβ Ag lines was captured and analyzed along with photoconducting diode (PCD) signals (>0.8 keV). Along with PCD signals, other signals, such as filtered XRD (>0.2 keV) and Si-diodes (SiD) (>9 keV), are analyzed covering a broad range of energies from a few eV to greater than 53 keV. The observation and analysis of cold Lα and Lβ lines show possible correlations with electron beams and SiD signals. Recently, an interesting issue regarding these Ag plasmas is whether lasing occurs in the Ne-like soft x-ray range, and if so, at what gains? To help answer this question, a non-local thermodynamic equilibrium (LTE) kinetic model was utilized to calculate theoretical lasing gains. It is shown that the Ag L-shell plasma conditions produced on the Zebra generator at 1.7 maximum current may be adequate to produce gains as high as 6 cm−1 for various 3p → 3s transitions. Other potential lasing transitions, including higher Rydberg states, are also included in detail. The overall importance of Ag wire arrays and plasmas is discussed.
Inner-shell radiation from wire array implosions on the Zebra generator
Authors: Ouart N. D. , Giuliani J. L. , Dasgupta A. , Safronova A. S. , Kantsyrev V. L. , Esaulov A. A. , Shrestha I. , Weller M. E. , Shlyaptseva V. , Osborne G. C. , Stafford A. , Keim S. , Apruzese J. P. , Clark R. W.
Published: March 2014

Implosions of brass wire arrays on Zebra have produced L-shell radiation as well as inner-shell Kα and Kβ transitions. The L-shell radiation comes from ionization stages around the Ne-like charge state that is largely populated by a thermal electron energy distribution function, while the K-shell photons are a result of high-energy electrons ionizing or exciting an inner-shell (1s) electron from ionization stages around Ne-like. The K- and L-shell radiations were captured using two time-gated and two axially resolved time-integrated spectrometers. The electron beam was measured using a Faraday cup. A multi-zone non-local thermodynamic equilibrium pinch model with radiation transport is used to model the x-ray emission from experiments for the purpose of obtaining plasma conditions. These plasma conditions are used to discuss some properties of the electron beam generated by runaway electrons. A simple model for runaway electrons is examined to produce the Kα radiation, but it is found to be insufficient.
Characterization of the fast electrons distribution produced in a high intensity laser target interaction
Authors: Westover B. , Chen C. D. , Patel P. K. , McLean H. , Beg F. N.
Published: March 2014

Experiments on the Titan laser (∼150 J, 0.7 ps, 2 × 1020 W cm−2) at the Lawrence Livermore National Laboratory were carried out in order to study the properties of fast electrons produced by high-intensity, short pulse laser interacting with matter under conditions relevant to Fast Ignition. Bremsstrahlung x-rays produced by these fast electrons were measured by a set of compact filter-stack based x-ray detectors placed at three angles with respect to the target. The measured bremsstrahlung signal allows a characterization of the fast electron beam spectrum, conversion efficiency of laser energy into fast electron kinetic energy and angular distribution. A Monte Carlo code Integrated Tiger Series was used to model the bremsstrahlung signal and infer a laser to fast electron conversion efficiency of 30%, an electron slope temperature of about 2.2 MeV, and a mean divergence angle of 39°. Simulations were also performed with the hybrid transport code ZUMA which includes fields in the target. In this case, a conversion efficiency of laser energy to fast electron energy of 34% and a slope temperature between 1.5 MeV and 4 MeV depending on the angle between the target normal direction and the measuring spectrometer are found. The observed temperature of the bremsstrahlung spectrum, and therefore the inferred electron spectrum are found to be angle dependent.
High energy conversion efficiency in laser-proton acceleration by controlling laser-energy deposition onto thin foil targets
Authors: Brenner C. M. , Robinson A. P. L. , Markey K. , Scott R. H. H. , Gray R. J. , Rosinski M. , Deppert O. , Badziak J. , Batani D. , Davies J. R. , Hassan S. M. , Lancaster K. L. , Li K. , Musgrave I. O. , Norreys P. A. , Pasley J. , Roth M. , Schlenvoigt H.-P. , Spindloe C. , Tatarakis M. , Winstone T. , Wolowski J. , Wyatt D. , McKenna P. , Neely D.
Published: March 2014

An all-optical approach to laser-proton acceleration enhancement is investigated using the simplest of target designs to demonstrate application-relevant levels of energy conversion efficiency between laser and protons. Controlled deposition of laser energy, in the form of a double-pulse temporal envelope, is investigated in combination with thin foil targets in which recirculation of laser-accelerated electrons can lead to optimal conditions for coupling laser drive energy into the proton beam. This approach is shown to deliver a substantial enhancement in the coupling of laser energy to 5–30 MeV protons, compared to single pulse irradiation, reaching a record high 15% conversion efficiency with a temporal separation of 1 ps between the two pulses and a 5 μm-thick Au foil. A 1D simulation code is used to support and explain the origin of the observation of an optimum pulse separation of ∼1 ps.
Signatures of hot electrons and fluorescence in Mo Kα emission on Z
Authors: Hansen S. B. , Ampleford D. J. , Cuneo M. E. , Ouart N. , Jones B. , Jennings C. A. , Dasgupta A. , Coverdale C. A. , Rochau G. A. , Dunham G. , Giuliani J. L. , Apruzese J. P.
Published: March 2014

Recent experiments on the Z accelerator have produced high-energy (17 keV) inner-shell K-alpha emission from molybdenum wire array z-pinches. Extensive absolute power and spectroscopic diagnostics along with collisional-radiative modeling enable detailed investigation into the roles of thermal, hot electron, and fluorescence processes in the production of high-energy x-rays. We show that changing the dimensions of the arrays can impact the proportion of thermal and non-thermal K-shell x-rays.
Multiple time step integrators in ab initio molecular dynamics
Authors: Luehr Nathan , Markland Thomas E. , Martínez Todd J.
Published: March 2014

Multiple time-scale algorithms exploit the natural separation of time-scales in chemical systems to greatly accelerate the efficiency of molecular dynamics simulations. Although the utility of these methods in systems where the interactions are described by empirical potentials is now well established, their application to ab initio molecular dynamics calculations has been limited by difficulties associated with splitting the ab initio potential into fast and slowly varying components. Here we present two schemes that enable efficient time-scale separation in ab initio calculations: one based on fragment decomposition and the other on range separation of the Coulomb operator in the electronic Hamiltonian. We demonstrate for both water clusters and a solvated hydroxide ion that multiple time-scale molecular dynamics allows for outer time steps of 2.5 fs, which are as large as those obtained when such schemes are applied to empirical potentials, while still allowing for bonds to be broken and reformed throughout the dynamics. This permits computational speedups of up to 4.4x, compared to standard Born-Oppenheimer ab initio molecular dynamics with a 0.5 fs time step, while maintaining the same energy conservation and accuracy.
Mössbauer spectroscopy, magnetic characteristics, and reflection loss analysis of nickel-strontium substituted cobalt ferrite nanoparticles
Authors: Ghasemi Ali , Paesano Andrea , Cerqueira Machado Carla Fabiana , Shirsath Sagar E. , Liu Xiaoxi , Morisako Akimitsu
Published: March 2014

In current research work, Co1-xNix/2Srx/2Fe2O4 (x = 0–1 in a step of 0.2) ferrite nanoparticles were synthesized by a sol-gel method. According to the evolution in the subspectral areas obtained from Mössbauer spectroscopy, it was found that the relaxing iron belongs mostly to the site B, since the Mössbauer fraction of site A does not vary appreciably. With an increase in Ni-Sr substitution contents in cobalt ferrite, the coercivity and saturation of magnetization decrease. Variation of reflection loss versus frequency in microwave X-band demonstrates that the reflection peak shifts to lower frequency by adding substituted cations and the synthesized nanoparticles can be considered for application in electromagnetic wave absorber technology.
Influence of hydrogen patterning gas on electric and magnetic properties of perpendicular magnetic tunnel junctions
Authors: Jeong J. H. , Endoh T. , Kim Y. , Kim W. K. , Park S. O.
Published: March 2014

To identify the degradation mechanism in magnetic tunnel junctions (MTJs) using hydrogen, the properties of the MTJs were measured by applying an additional hydrogen etch process and a hydrogen plasma process to the patterned MTJs. In these studies, an additional 50 s hydrogen etch process caused the magnetoresistance (MR) to decrease from 103% to 14.7% and the resistance (R) to increase from 6.5 kΩ to 39 kΩ. Moreover, an additional 500 s hydrogen plasma process decreased the MR from 103% to 74% and increased R from 6.5 kΩ to 13.9 kΩ. These results show that MTJs can be damaged by the hydrogen plasma process as well as by the hydrogen etch process, as the atomic bonds in MgO may break and react with the exposed hydrogen gas. Compounds such as MgO hydrate very easily. We also calculated the damaged layer width (DLW) of the patterned MTJs after the hydrogen etching and plasma processes, to evaluate the downscaling limitations of spin-transfer-torque magnetic random-access memory (STT-MRAM) devices. With these calculations, the maximum DLWs at each side of the MTJ, generated by the etching and plasma processes, were 23.8 nm and 12.8 nm, respectively. This result validates that the hydrogen-based MTJ patterning processes cannot be used exclusively in STT-MRAMs beyond 20 nm.
Measurement of FePt thermal properties relevant to heat-assisted magnetic recording
Authors: Chernyshov Alex , Treves David , Le Thanh , Zong Fenghua , Ajan Antony , Acharya Ramamurthy
Published: March 2014

Heat-assisted magnetic recording (HAMR) is the likely successor of the conventional perpendicular magnetic recording. Due to its high anisotropy, graded L10 ordered FePt is widely used as a HAMR recording layer. Electrically insulating MgO under-layer is essential for growing FePt in HAMR media. Experimentally, we observe very low thermal conductivity of FePt and significant thermal boundary resistance between FePt and MgO, whose magnitudes affect the HAMR thermal gradient. Realistic granular FePt media has >30% segregation, and, experimentally, we observe that FePt thermal properties are affected by segregation. We utilized time domain thermo-reflectance (TDTR) technique for studying FePt thermal conductivity and boundary resistance in realistic HAMR media stack. 1D finite element heat transport model was used for fitting experimental TDTR data and extracting thermal conductivities and related thermal boundary resistances. We found best fit thermal conductivity value for non-segregated FePt is as low as 13 W/mK. When reasonable amount of segregation (30%) is added, thermal conductivity reduces from 13 W/mK to 6 W/mK, and thermal boundary resistance to MgO reduces from 3.5 × 10−9 m2K/W to 0.7 × 10−9 m2K/W.