bluuebunny/crossref_metadata_2025 huggingface dataset:
Metabolic and Environmental Conditions Determine Nuclear Genomic Instability in Budding Yeast Lacking Mitochondrial DNA
Authors: Dirick Léon , Bendris Walid , Loubiere Vincent , Gostan Thierry , Gueydon Elisabeth , Schwob Etienne
Published: January 2014

Mitochondrial dysfunctions are an internal cause of nuclear genome instability. Because mitochondria are key regulators of cellular metabolism, we have investigated a potential link between external growth conditions and nuclear chromosome instability in cells with mitochondrial defects. Using Saccharomyces cerevisiae, we found that cells lacking mitochondrial DNA (rho0 cells) have a unique feature, with nuclear chromosome instability that occurs in nondividing cells and strongly fluctuates depending on the cellular environment. Calorie restriction, lower growth temperatures, growth at alkaline pH, antioxidants (NAC, Tiron), or presence of nearby wild-type cells all efficiently stabilize nuclear genomes of rho0 cells, whereas high glucose and ethanol boost instability. In contrast, other respiratory mutants that still possess mitochondrial DNA (RHO+) keep fairly constant instability rates under the same growth conditions, like wild-type or other RHO+ controls. Our data identify mitochondrial defects as an important driver of nuclear genome instability influenced by environmental factors.
A Bayesian MCMC Approach to Assess the Complete Distribution of Fitness Effects of New Mutations: Uncovering the Potential for Adaptive Walks in Challenging Environments
Authors: Bank Claudia , Hietpas Ryan T , Wong Alex , Bolon Daniel N , Jensen Jeffrey D
Published: January 2014

The role of adaptation in the evolutionary process has been contentious for decades. At the heart of the century-old debate between neutralists and selectionists lies the distribution of fitness effects (DFE)—that is, the selective effect of all mutations. Attempts to describe the DFE have been varied, occupying theoreticians and experimentalists alike. New high-throughput techniques stand to make important contributions to empirical efforts to characterize the DFE, but the usefulness of such approaches depends on the availability of robust statistical methods for their interpretation. We here present and discuss a Bayesian MCMC approach to estimate fitness from deep sequencing data and use it to assess the DFE for the same 560 point mutations in a coding region of Hsp90 in Saccharomyces cerevisiae across six different environmental conditions. Using these estimates, we compare the differences in the DFEs resulting from mutations covering one-, two-, and three-nucleotide steps from the wild type—showing that multiple-step mutations harbor more potential for adaptation in challenging environments, but also tend to be more deleterious in the standard environment. All observations are discussed in the light of expectations arising from Fisher’s geometric model.
The Impact of Accelerating Faster than Exponential Population Growth on Genetic Variation
Authors: Reppell Mark , Boehnke Michael , Zöllner Sebastian
Published: January 2014

Current human sequencing projects observe an abundance of extremely rare genetic variation, suggesting recent acceleration of population growth. To better understand the impact of such accelerating growth on the quantity and nature of genetic variation, we present a new class of models capable of incorporating faster than exponential growth in a coalescent framework. Our work shows that such accelerated growth affects only the population size in the recent past and thus large samples are required to detect the models’ effects on patterns of variation. When we compare models with fixed initial growth rate, models with accelerating growth achieve very large current population sizes and large samples from these populations contain more variation than samples from populations with constant growth. This increase is driven almost entirely by an increase in singleton variation. Moreover, linkage disequilibrium decays faster in populations with accelerating growth. When we instead condition on current population size, models with accelerating growth result in less overall variation and slower linkage disequilibrium decay compared to models with exponential growth. We also find that pairwise linkage disequilibrium of very rare variants contains information about growth rates in the recent past. Finally, we demonstrate that models of accelerating growth may substantially change estimates of present-day effective population sizes and growth times.
A Genome-Wide Scan for Evidence of Selection in a Maize Population Under Long-Term Artificial Selection for Ear Number
Authors: Beissinger Timothy M , Hirsch Candice N , Vaillancourt Brieanne , Deshpande Shweta , Barry Kerrie , Buell C Robin , Kaeppler Shawn M , Gianola Daniel , de Leon Natalia
Published: January 2014

A genome-wide scan to detect evidence of selection was conducted in the Golden Glow maize long-term selection population. The population had been subjected to selection for increased number of ears per plant for 30 generations, with an empirically estimated effective population size ranging from 384 to 667 individuals and an increase of more than threefold in the number of ears per plant. Allele frequencies at >1.2 million single-nucleotide polymorphism loci were estimated from pooled whole-genome resequencing data, and FST values across sliding windows were employed to assess divergence between the population preselection and the population postselection. Twenty-eight highly divergent regions were identified, with half of these regions providing gene-level resolution on potentially selected variants. Approximately 93% of the divergent regions do not demonstrate a significant decrease in heterozygosity, which suggests that they are not approaching fixation. Also, most regions display a pattern consistent with a soft-sweep model as opposed to a hard-sweep model, suggesting that selection mostly operated on standing genetic variation. For at least 25% of the regions, results suggest that selection operated on variants located outside of currently annotated coding regions. These results provide insights into the underlying genetic effects of long-term artificial selection and identification of putative genetic elements underlying number of ears per plant in maize.
Morphometric Variation Affecting Sexual Size Dimorphism in Neopedies brunneri (Orthoptera: Acrididae)
Authors: Romero María Luciana , Rosetti Natalia , Remis María Isabel
Published: January 2014

Neopedies brunneri (Giglio-Tos, 1894) is a grasshopper belonging to the family Acrididae. This group of insects usually has economic importance in Argentina because of their ability to experience outbreaks, but little is known about them. Insect populations usually differ at the phenotypic level, often according to geographical and environmental variables, which may be a good indicator of some other factors with adaptive significance (such as developmental rate, seasonal resource disposal, and growing seasonal length). The aim of this article is to report the first preliminary analysis of phenotypic variation in natural populations of N. brunneri from central Argentina to study the amount of intra- and interpopulation variation in morphometric traits and their probable association with geographic and climatic variables.Wefound the existence of morphometrical differences among populations and a pattern of geographical variation, with males and females from eastern populations being larger than the ones from the west. Sexual size dimorphism was also detected and found to be correlated to geographical and climactic variation. Moreover, geographic patterns of sexual size dimorphism were determined, helping to clarify differential susceptibility of both sexes to environmental conditions.
Assessing predictions of population viability analysis: Peregrine Falcon populations in California
Authors: Wootton J. Timothy , Bell Douglas A.
Published: January 2014

Population viability analysis (PVA) has been an important tool for evaluating species extinction risk and alternative management strategies, but there is little information on how well PVA predicts population trajectories following changes in management actions. We tested previously published predictions from a stage‐structured PVA of Peregrine Falcons (Falco peregrinus) in California, USA (Wootton and Bell 1992), against population trajectories following the 1992 termination of statewide, active management (population supplementation of captive‐reared young). In the absence of extensive post‐management monitoring, we developed surrogate estimates of breeding population size by calibrating several citizen science data sets (Christmas Bird Count, CBC; and North American Breeding Bird Survey, BBS) to intensive population surveys taken primarily during the active management period. CBC abundance data standardized by observer effort exhibited a strong relationship to intensive survey data (r2 = 0.971), indicated significantly reduced annual population growth rates after management was terminated (λ = 0.023 ± 0.013 SE) than when supplementation occurred (λ = 0.089 ± 0.023 SE), and demonstrated an increasing population as predicted by the PVA. The population trajectory fell within the 95% CI of stochastic simulations of the model either with or without density dependence and assuming either measurement error or process error, but models with process error were most strongly supported by the data. These results indicate that PVA can quantitatively anticipate population trajectories following changes in management, highlight the importance of post‐management monitoring of species of concern, and illustrate the benefits of using management changes as large‐scale experiments to more rigorously test PVA.
Novel Method for Characterizing Single-Phase Polymer Flooding
Authors: Li Kewen , Sun Wenjie , Li Fen , Qu Yantao , Yang Yaozhong
Published: January 2014

Polymer flooding has been used to enhance oil production and reduce water cut for a long time. However, there are still many fundamental challenges in characterizing the multiphase-fluid flow, even the single-phase-fluid flow, associated with polymer flooding. For example, it is difficult to measure and calculate two-phase polymer solution/oil relative permeability. One of the difficulties comes from the non-Newtonian and time-dependent properties of polymer solutions; another comes from the change in absolute permeability caused by the adsorption of polymer on rock surfaces. Almost all the methods for computing relative permeability are based on the assumption that the absolute permeability is constant. It may be helpful to further understand the mechanisms and develop more-reliable methods for calculating two-phase polymer solution/oil relative permeability by investigating single-phase polymer flooding more profoundly. In this study, a new method has been developed to calculate the pseudopermeability during single-phase polymer flooding. The non-Newtonian property of the polymer solutions was considered in the new method. Polymer-flooding experiments with different concentrations of polymers were designed and conducted to study the single-phase flow of polymer solution in rocks with different permeabilities. The values of the pseudopermeability of single-phase polymer flooding were then calculated with the method. It has been found that the relationships between the pseudopermeability and the reciprocal of shear rate were linear. The polymer-flooding pseudopermeability extrapolated at the infinite shear rate was close to the brine-flooding permeability after polymer injections in many cases.
Switchable Nonionic to Cationic Ethoxylated Amine Surfactants for CO2 Enhanced Oil Recovery in High-Temperature, High-Salinity Carbonate Reservoirs
Authors: Chen Yunshen , Elhag Amro S. , Poon Benjamin M. , Cui Leyu , Ma Kun , Liao Sonia Y. , Reddy Prathima P. , Worthen Andrew J. , Hirasaki George J. , Nguyen Quoc P. , Biswal Sibani L. , Johnston Keith P.
Published: January 2014

To improve sweep efficiency for carbon dioxide (CO2) enhanced oil recovery (EOR) up to 120°C in the presence of high-salinity brine (182 g/L NaCl), novel CO2/water (C/W) foams have been formed with surfactants composed of ethoxylated amine headgroups with cocoalkyl tails. These surfactants are switchable from the nonionic (unprotonated amine) state in dry CO2 to cationic (protonated amine) in the presence of an aqueous phase with a pH less than 6. The high hydrophilicity in the protonated cationic state was evident in the high cloudpoint temperature up to 120°C. The high cloud point facilitated the stabilization of lamellae between bubbles in CO2/water foams. In the nonionic form, the surfactant was soluble in CO2 at 120°C and 3,300 psia at a concentration of 0.2% (w/w). C/W foams were produced by injecting the surfactant into either the CO2 phase or the brine phase, which indicated good contact between phases for transport of surfactant to the interface. Solubility of the surfactant in CO2 and a favorable C/W partition coefficient are beneficial for transport of surfactant with CO2-flow pathways in the reservoir to minimize viscous fingering and gravity override. The ethoxylated cocoamine with two ethylene oxide (EO) groups was shown to stabilize C/W foams in a 30-darcy sandpack with NaCl concentrations up to 182 g/L at 120°C and 3,400 psia, and foam qualities from 50 to 95%. The foam produces an apparent viscosity of 6.2 cp in the sandpack and 6.3 cp in a 762-μm-inner-diameter capillary tube (downstream of the sandpack) in contrast with values well below 1 cp without surfactant present. Moreover, the cationic headgroup reduces the adsorption of ethoxylated alkyl amines on calcite, which is also positively charged in the presence of CO2 dissolved in brine. The surfactant partition coefficients (0 to 0.04) favored the water phase over the oil phase, which is beneficial for minimizing losses of surfactant to the oil phase for efficient surfactant usage. Furthermore, the surfactant was used to form C/W foams, without forming stable/viscous oil/water (O/W) emulsions. This selectivity is desirable for mobility control whereby CO2 will have low mobility in regions in which oil is not present and high contact with oil at the displacement front. In summary, the switchable ethoxylated alkyl amine surfactants provide both high cloudpoints in brine and high interfacial activities of ionic surfactants in water for foam generation, as well as significant solubilities in CO2 in the nonionic dry state for surfactant injection.
Rapid Updating of Stochastic Models by Use of an Ensemble-Filter Approach
Authors: Tavakoli Reza , Srinivasan Sanjay , Wheeler Mary F.
Published: January 2014

Applying an ensemble Kalman filter (EnKF) is an effective method for reservoir history matching. The underlying principle is that an initial ensemble of stochastic models can be progressively updated to reflect measured values as they become available. The EnKF performance is only optimal, however, if the prior-state vector is linearly related to the predicted data and if the joint distribution of the prior-state vector is multivariate Gaussian. Therefore, it is challenging to implement the filtering scheme for non-Gaussian random fields, such as channelized reservoirs, in which the continuity of permeability extremes is well-preserved. In this paper, we develop a methodology by combining model classification with multidimensional scaling (MDS) and the EnKF to create rapidly updating models of a channelized reservoir. A dissimilarity matrix is computed by use of the dynamic responses of ensemble members. This dissimilarity matrix is transformed into a lower-dimensional space by use of MDS. Responses mapped in the lower-dimension space are clustered, and on the basis of the distances between the models in a cluster and the actual observed response, the closest models to the observed response are retrieved. Model updates within the closest cluster are performed with EnKF equations. The results of an update are used to resample new models for the next step. Two-dimensional, waterflooding examples of channelized reservoirs are provided to demonstrate the applicability of the proposed method. The obtained results demonstrate that the proposed algorithm is viable both for sequentially updating reservoir models and for preserving channel features after the data-assimilation process.
Tie-Simplex-Based Phase-Behavior Modeling in an IMPEC Reservoir Simulator
Authors: Rezaveisi M.. , Sepehrnoori K.. , Johns R.T.. T.
Published: January 2014

Recently, tie-simplex-based phase-behavior modeling in reservoir simulators has been applied and investigated as a potential method for improving the computational speed of equation-of-state (EOS) -based reservoir simulators. We implemented compositional-space adaptive tabulation (CSAT), the most promising tie-simplex-based method, in UTCOMP, the University of Texas' in-house IMPEC compositional reservoir simulator, to investigate its computational efficiency compared with the phase-behavior algorithm in UTCOMP. The results show that applying CSAT only to skip stability analysis does improve computational time, but only when a significant portion of the gridblocks are in the single-phase region and no other technique for avoiding stability analysis is used. However, in most cases, there is little or no computational advantage to use of CSAT when the simple option in UTCOMP is used where stability analysis is skipped for blocks surrounded by single-phase regions. We explore in detail the performance of CSAT, which depends significantly on the specific gas flood modeled, and the number of tie-lines generated during adaptive tabulation. The results shed light on applicability of CSAT in the IMPEC-type compositional reservoir simulators and show that the advantages of CSAT in this type of simulator are not as great as are reported in the literature for fully implicit or adaptive implicit formulations.
Effect of Elemental-Sulfur Deposition on the Rock Petrophysical Properties in Sour-Gas Reservoirs
Authors: Mahmoud M.A.. A.
Published: January 2014

The deposition of elemental sulfur as a solid phase results in plugging the pore space available for gas flow and reduces the reservoir productivity. Elemental sulfur also can be deposited as a liquid phase if the reservoir temperature is greater than 115°C. The liquid sulfur restricts the inflow of gas because of the big density difference between liquid sulfur and gas, which could be 20 times or more. For isothermal conditions in the reservoir, the reduction in reservoir pressure to lower than a critical value causes the elemental sulfur to deposit in the formation, and in turn the gas-well productivity is affected. Accurate prediction of sulfur deposition will help better manage sour-gas reservoirs with potential sulfur-deposition problems.

In this paper, a new analytical model was developed to predict the effect of sulfur deposition on the damage of the near-wellbore region. The damage was quantified through the investigation of the effect of sulfur deposition on rock porosity, relative permeability of the gas phase, and the change in rock wettability. The main objective of this model is to investigate the effect of radial distance on formation damage. Different rock- and fluid-property correlations were used in the model. Previous studies did not consider the change in gas properties with pressure, and numerically modeled the sulfur deposition as a condensate in a gas/condensate reservoir. This paper will consider sulfur adsorption, and the actual physical properties of the sulfur will be used in the developed model. The optimum gas-flow velocity that will maximize the sulfur solubility in the gas will be determined. A coreflood experiment was performed to determine the effect of sulfur deposition on the carbonate-rock permeability, porosity, and wettability. The experiment was used to determine the effect of sulfur adsorption on the rock petrophysical properties. The contact angle was measured for a carbonate core saturated with sulfur by use of a pendant-drop tensiometer.

Analytical and numerical solutions showed that the deposition of sulfur was affected by the radial distance from the wellbore and sulfur-solubility changes as a function of the pressure drop. Sulfur deposition was found to have a great effect on the rock wettability, and in turn the gas production will be affected. The model can be used to predict the critical flow velocity that the gas can flow without precipitating sulfur. The optimum gas-flow velocity was estimated to be a range that maximizes the sulfur solubility in the gas. It was confirmed experimentally that the sulfur deposition reduced the carbonate-core porosity and permeability, and changed the contact angle (rock wettability). The contact angle increased, which means sulfur adsorption on the rock surfaces changed the rock toward more-gas-wet rock.
Integration and Assurance of Well Documents and Data—Essential Preparation for Tomorrow
Authors: Sawaryn S.J.. J. , Pirie L.. , Green I.. , Scott A.. , Cosgrove B.. , Emslie I..
Published: January 2014

During the last 4 years, more than 330,000 electronic drilling, completion, and intervention documents have been consolidated in a new document-management system, improving both their accessibility and future worth to the expanding base of users. The system's document structure builds on earlier, engineer-led experience and has contributed to the new companywide standard for managing these documents. At the same time, the document-management project has eliminated more than 180,000 duplicate or obsolete documents.

As part of the migration from the old system to the new one, common well names have been adopted to support integration activities within the wells' functional organization and the subsurface and operations communities. Directional surveys are key links between these communities, and over the same period, an in-depth, field-by-field review of the company's UK directional-survey data has been conducted. This activity is now approximately 67% complete. Together, these activities are seen as essential preparations for the future, and they have already helped streamline some activities in both asset acquisitions and disposals.

These tasks took time, but measured preparation plus a degree of pragmatism have ensured they remain manageable. Care has been taken to maintain the document folder structure so it remains familiar to users while also taking advantage of the superior capabilities, such as search and assurance, available in the new system. This paper contains an outline of the structure and metadata and a description of the project's goals and history, including some of the challenges commonly encountered in preparing, processing, and exporting and importing data. Details of the directional-survey data-verification process are also provided.

This subject is of interest to many companies because of the scale of the exercise and the growing recognition in the industry of its technical and commercial importance.
Properties of a Natural Fracture and Its Skins From Reservoir Well Tests
Authors: Prats M.. , Raghavan R..
Published: January 2014

Two well tests are described that are aimed at the in-situ determination of the flow capacity (permeability-thickness product) of a natural fracture and the flow resistance of its skins at the boundaries with the reservoir matrix. Fracture skins tend to disperse flow, thus affecting the distribution of tracers in reservoir tests and contaminants and trace elements in aquifers. We are unaware of any other analytical procedure aimed at obtaining the properties of a natural fracture and its skins from subsurface measurements. Neither well test has been implemented.

The well tests are modeled after previously reported analytical expressions for the transient pressure distributions in a three-region composite reservoir in a uniform-thickness reservoir in which (1) the natural fracture is represented by a thin middle region of relatively high permeability, (2) the pressure disturbance is caused by producing from a short interval in one of the outer regions, and (3) the response is measured relatively near the fracture. The source and sensor may be on the same side or on opposite sides of the fracture, distinguishing the two tests.

Visualizing special completions in a horizontal well intersecting a natural fracture normally, pressure responses are given for both tests for a wide range of fracture/matrix permeability ratios and skin flow resistances for a source 190 ft from the fracture and 10 ft from the sensor and on either side of the fracture, both at the midplane of the reservoir.

A simple graphical procedure, not intended to replace history matching or regression where field data are available, illustrates how the two unknowns—permeability-thickness product of a natural fracture and the flow resistance of its skins—may be estimated from two representative values of an assumed measured pressure response.
Applying Method of Characteristics to Determine Pressure Distribution in 1D Shale-Gas Samples
Authors: Moghanloo R. Ghanbarnezhad , Javadpour F..
Published: January 2014

This paper examines application of the method of characteristics (MOC) to determine pressure distribution in a 1D matrix of shale gas. Because of gas expansion and local desorption in shale gas, pressure distribution changes during production. We developed a semianalytic MOC solution of gas flow in shale by use of the analogous-continuum approximation (apparent permeability). The MOC solution is derived with the inclusion of compressibility, gas-slippage effect, and desorption.

Through quantitative comparison of pressure profiles and history plots, we used a simulation approach to verify the accuracy of the analytic solution. Results suggest that the simulation results are consistent with our MOC solution, which can also be used to evaluate impacts of different parameters on pressure distribution. Prediction of pressure distribution over time will greatly enhance approximation of reservoir performance.
Laplace-Transform Finite-Difference and Quasistationary Solution Method for Water-Injection/Falloff Tests
Authors: Habte Azeb D. , Onur Mustafa
Published: January 2014

In this work, we present a method for efficiently and accurately simulating the pressure-transient behavior of oil/water flow associated with water-injection/falloff tests. The method uses the Laplace-transform finite-difference (LTFD) method coupled with the well-known Buckley-Leverett frontal-advance formula to solve the radial diffusivity equation describing slightly compressible oil/water two-phase flow. The method is semianalytical in time, and as a result, the issue of time discretization in the finite-difference approximation method is eliminated. Thus, stability and convergence problems caused by time discretization are avoided. Two approaches are presented and compared in terms of accuracy for simulating the tests with multiple-rate injection and falloff periods: One is based on solving the initial-boundary-value (IVB) problem with the initial condition attained from the end of the previous flow period, and the other is based on the conventional superposition on the basis of the single-phase flow of a slightly compressible fluid. The former is shown to always provide a more accurate and efficient solution. The method is quite general in that it allows one to incorporate the effect of wellbore storage and thick-skin and finite outer-boundary conditions. The accuracy of the method was evaluated by considering various synthetic test cases with favorable and unfavorable mobility ratios and by comparing the pressure and pressure-derivative signatures with a commercial black-oil simulator, and an excellent agreement was seen.
Laser-induced thermoelectric voltage in La0.9Pr0.1MnO3 thin films
Authors: Zhang Lisheng , Hua Qianqian , Fang Yan
Published: January 2014

The laser-induced thermoelectric voltage (LITV) was observed in La0.9Pr0.1MnO3 thin films grown on the vicinal cut LaAlO3 substrate by pulsed laser deposition for the first time. The detected signals were demonstrated to be originated from the anisotropic Seebeck effect. The largest peak value of the voltage is about 2.4 V, the full width at half-maximum of the temporal voltage peak and the rising time are 300–500 and 40–50 ns, respectively. It is a high quality and efficient material in the LITV family.
Use of track/layer morphology to develop functional parts by selective laser melting
Authors: Yadroitsev I. , Bertrand Ph. , Antonenkova G. , Grigoriev S. , Smurov I.
Published: January 2014

Selective laser melting (SLM) is a powder-based additive manufacturing capable to produce parts layer-by-layer from a 3D computer-aided design model. Currently, there is a growing interest in industry for applying this technology for generating objects with high geometrical complexity. To introduce SLM process into industry for manufacturing real components, excellent mechanical properties and high functionality of final product must be achieved. Properties of the manufactured parts depend strongly on each single laser-melted track and each single layer, as well as the strength of the connections between them. In this study, effects of the processing parameters such as hatch distance, layer thickness, laser power, scanning speed on surface morphology, and surface texturing are analyzed.
Investigation into the effects of process parameters on bending angle in the laser bending of tailor machined blanks based on a statistical analysis
Authors: Safari Mehdi , Farzin Mahmoud , Ghaei Abbas
Published: January 2014

In this paper, the effects of process parameters on bending angle in laser bending of tailor machined blanks are investigated experimentally. The Taguchi experimental design method is employed to study various parameters, which significantly affect the bending angle in the laser bending of tailor machined blanks. The start point of scan path, irradiating method, laser output power, beam diameter, and number of radiation passes are considered in the evaluations. A L18(21×34) Taguchi standard orthogonal array is chosen for the design of experiments. The level of importance of the process parameters on the bending angle is determined by using analysis of variance. The optimum process parameters combination is obtained by using the analysis of signal-to-noise (S/N) ratios. The variation of bending angle with process parameters is mathematically modeled by using the regression analysis method and a closed form equation is derived. The results show irradiating method, laser output power, beam diameter, number of radiation passes, and start point of scan path have the most importance effects on bending angle, respectively. It is concluded from results that irradiating method has the most important effect on bending angle. After irradiating method, laser output power, beam diameter, number of radiation passes, and start point of scan path have the most important effects on bending angle, respectively. Therefore, selecting a suitable irradiating method can noticeably improve the bending angle in the laser bending of tailor machined blanks.
Laser remote-fusion cutting with solid-state lasers
Authors: Wagner A. , Lütke M. , Wetzig A. , Eng L. M.
Published: January 2014

A laser remote cutting process is analyzed, which differs significantly from established laser cutting processes. On the one hand, no cutting gas is needed and a high working distance is realized. On the other hand—in opposite to conventional laser remote cutting—sheets of metal with thicknesses above 1 mm can be cut in one step. Examinations were carried out at the martensitic boron steel 22MnB5 due to its interesting applications at automotive industry and significant advantages of the presented cutting process. Large focal spots and low cutting velocities are needed when moving the laser beam over the surface of the work-piece. Mainly, the material is melted besides a little fraction of vapor, which forms a keyhole, comparable with laser deep penetration welding. Besides typical parameters, the behavior of the ejection of melt is presented. The melt exits the kerf characteristically in beam direction at the bottom of the work-piece but changes its axial direction. Therefore, two subprocesses are defined and examined separately: Subprocess A can be observed at low cutting velocities and is characterized by a pushing melt ejection, whereas subprocess B needs significantly higher velocities and results in dragging melt ejection.
Heat transfer and fluid flow in additive manufacturing
Authors: Raghavan A. , Wei H. L. , Palmer T. A. , DebRoy T.
Published: January 2014

In laser-based direct energy deposition additive manufacturing, process control can be achieved through a closed loop control system in which thermal sensing of the melt pool surface is used to adjust laser processing parameters to maintain a constant surface geometry. Although this process control technique takes advantage of important in-process information, the conclusions drawn about the final solidification structure and mechanical properties of the deposited material are limited. In this study, a validated heat transfer and fluid flow laser welding model are used to examine how changes in processing parameters similar to those used in direct energy deposition processes affect the relationships between top surface and subsurface temperatures and solidification parameters in Ti-6Al-4V. The similarities between the physical processes governing laser welding and laser-based additive manufacturing make the use of a laser welding model appropriate. Numerical simulations show that liquid pools with similar top surface geometries can have substantially different penetration depths and volumes. Furthermore, molten pool surface area is found to be a poor indicator of the cooling rate at different locations in the melt pool and, therefore, cannot be relied upon to achieve targeted microstructures and mechanical properties. It is also demonstrated that as the build temperature increases and the power level is changed to maintain a constant surface geometry, variations in important solidification parameters are observed, which are expected to significantly impact the final microstructure. Based on the results, it is suggested that the conclusions drawn from current experimental thermography control systems can be strengthened by incorporating analysis through mathematical modeling.
Numerical and experimental study of the effect of groove on plasma plume during high power laser welding
Authors: Yan Cai , Wen-Jing Xie , Yue Wu , Da-Wei Sun , Yixiong Wu
Published: January 2014

The influence of groove on the static feature and dynamic behavior of plasma plume during high power CO2 laser welding process was studied using a hydrodynamic three-dimensional model and corresponding experiments. The temperature, composition, and velocity of plasma plume along the incident path of laser beam were computed. The static morphology of plasma plume was analyzed through both models and comparative experiments. The difference of dynamic behavior of plasma plume between inside groove and on-plate was studied based on plume images taken by high-speed camera. The results showed that the groove could significantly affect the characteristics of plasma plume including static morphology, dynamic behavior, the coupling of laser energy, and resultant weld penetration. Modeling results concerning the influence of groove on plasma characteristics were reasonably consistent with experiment results.
Review study on remote laser welding with fiber lasers
Authors: Lu Jinhong , Kujanpää Veli
Published: January 2014

The appearance of the high-power fiber laser with brilliant beam quality enables a rapid development of remote laser welding (RLW). In this paper, a theoretical study of remote laser welding has been reviewed. As a promising technology, the RLW offers an increased flexibility, high operational speed, and reduced cycle time to process a wide range of workpieces. This study presents the feasibility and typical characteristics of RLW with high-power fiber lasers. Meanwhile, the influence of process parameters, such as laser power, welding speed, shielding gas supply, beam inclination, and focal position, on the weld seam quality has been investigated.
Crack-free laser dicing of glass in the microelectronics industry
Authors: Savriama Guillaume , Mendez José , Barreau Laurent , Boulmer-Leborgne Chantal , Semmar Nadjib
Published: January 2014

This paper investigates laser dicing of glass (commercial Borofloat®33) for backend packaging in the microelectronics industry. An ultraviolet (355 nm) diode-pumped solid-state nanosecond laser was used in this investigation. Laser processing of glass is challenging as glass is transparent for most available wavelengths. Nonlinear absorption can be obtained but produces undesirable effects (chipping, cracks) in the nanosecond regime. In the present study, an absorptive polymer layer was spin coated on top of the substrate and acts as a heat incubator during laser irradiation. This paper shows that preheating the substrate produces clean scribe. Laser dicing is qualitatively and quantitatively more efficient than blade sawing. 1 × 1 mm2 dice have been separated by laser scribe/break method that allows a throughput increase of 18%versus blade sawing.
Stoichiometric 6H-SiC thin films deposited at low substrate temperature by laser ablation
Authors: Quiñones-Galván J. G. , Arias-Cerón J. S. , de Moure-Flores F. , Hernández-Hernández A. , Guillén-Cervantes A. , Santoyo-Salazar J. , Mendoza-Alvarez J. G. , Meléndez-Lira M.
Published: January 2014

Silicon carbide thin films were grown by laser ablation on silicon substrates at different deposition temperatures using SiC powders as target material. The structural, morphological, compositional, and optical properties were studied as a function of the deposition temperature. The 6H-SiC crystalline phase was observed by Raman spectroscopy, x-ray diffraction, and transmission electron diffraction without the presence of any other polytype. In the room temperature photoluminescence spectra, a broad band was observed in the visible region which suggests that these films can have applications on silicon based optoelectronics.
Femtosecond laser post-processing of metal parts produced by laser additive manufacturing
Authors: Mingareev Ilya , Bonhoff Tobias , El-Sherif Ashraf F. , Meiners Wilhelm , Kelbassa Ingomar , Biermann Tim , Richardson Martin
Published: January 2014

High-repetition rate femtosecond laser radiation was utilized to improve surface quality of metal parts manufactured by laser additive techniques. Different laser scanning approaches were utilized to increase the ablation efficiency and to improve the surface finish. Processing of 3D-shaped parts made of titanium- and nickel-base alloys resulted in the reduction of the average surface roughness to a few microns. This approach can be used to post-process parts made of thermally and mechanically sensitive materials and to attain complex designed shapes with micrometer precision. Advantages and limitations of this novel post-processing technique are discussed.
Periodic antireflection surface structure fabricated on silicon by four-beam laser interference lithography
Authors: Zhang Z. , Wang Z. , Wang D. , Ding Y.
Published: January 2014

Silicon surface structures with excellent antireflection property arouse wide interest. Chemical and physical methods such as femtosecond, nanosecond, and picosecond laser processing, wet-chemical etching, electrochemical etching, and reactive ion etching have been developed to fabricate them. However, the methods can only produce a quasi-ordered array of sharp conical microspikes on silicon surface. In this paper, we present a method to fabricate periodic silicon antireflection surface structures using direct four-beam laser interference lithography (LIL). With 1 atm ambient atmosphere of SF6 and the laser fluence of the four beams irradiated on the silicon surface at 0.64 J cm−2, the periodical conical spikes were generated. Changing the polarization directions of the opposite incident beam pairs in a four-beam LIL system could convert conical spikes structure into an array of holes. Antireflection in a wide spectral range was measured by a spectrophotometer from ultraviolet to near-infrared. The average reflectance of this periodic black silicon surface is less than 3.5%.
Clinical Decision Making for Low Back Pain: A Step in the Right Direction
Authors: Childs John D. , Flynn Timothy W.
Published: January 2014

This month's issue of JOSPT includes a paper by Dr Alon Rabin and colleagues that attempts to validate a clinical prediction rule (CPR) originally developed several years ago to identify patients with low back pain likely to benefit from lumbar stabilization exercise. Regardless of one's bias as to when decision-making rules (or, perhaps better, aids) are useful for clinical decision making, few can disagree that it is beneficial to see the evolution of this CPR past the initial development stage and now into step 2 of the development process. As with all research, this study asks more questions than it answers. However, as clinicians, we now have more information on which to make decisions about the patient sitting in front of us. We believe we can all agree that this is a positive step in the right direction. J Orthop Sports Phys Ther 2014;44(1):1–2. doi:10.2519/jospt.2014.0101
JOSPT at 35
Authors: Simoneau Guy G. , Holmes Edith
Published: January 2014

The year 2014 marks the 35th anniversary of the Journal of Orthopaedic & Sports Physical Therapy. Begun on a kitchen table in 1979, JOSPT is now the top-ranked physical therapy journal in the categories of rehabilitation, orthopaedics, and sports sciences. JOSPT has grown into its tagline: “The Global Resource for Musculoskeletal Health, Injury, and Rehabilitation.” We will work to continue to be this resource in the year ahead—certainly for the physical therapy profession, but also for the broader health care community. J Orthop Sports Phys Ther 2014;44(1):3–5. doi:10.2519/jospt.2014.0102
Ganglion Cyst in the Tarsal Tunnel
Authors: Farber Daniel C. , Lovering Richard M.
Published: January 2014

The patient was a 35-year-old man who worked as a pipe fitter. He was referred to a physical therapist by an orthopaedic surgeon for a chief complaint of progressively worsening pain in the medial aspect of the right distal Achilles tendon and heel that began insidiously 12 months earlier, which was consistent with a diagnosis of insertional Achilles tendonitis. Prior radiographs revealed mild calcification at the insertion of the Achilles tendon. Despite physical therapist intervention for 8 weeks, the patient did not improve. Subsequent magnetic resonance imaging revealed a large multiloculated ganglion cyst in the tarsal tunnel. J Orthop Sports Phys Ther 2014;44(1):40. doi:10.2519/jospt.2014.0401
Snapping Pes Anserine Syndrome
Authors: Rainey Charles E. , Taysom Danielle A. , Rosenthal Michael D.
Published: January 2014

The patient was a 25-year-old man who was serving in the military. He was referred to a physical therapist for a progressively worsening painful snapping sensation in the posteromedial left knee region. Prior magnetic resonance imaging for the left knee was interpreted as normal, except for a mild fluid signal about the left pes anserine bursa. The patient was diagnosed with snapping pes anserine syndrome. However, despite 6 weeks of physical therapist intervention, the patient did not improve. A dynamic real-time ultrasound examination was then ordered, which demonstrated that the pes anserine tendons changed position as the knee moved from flexion to extension, sliding across a heterogeneous rounded mass in the posteromedial knee. J Orthop Sports Phys Ther 2014;44(1):41. doi:10.2519/jospt.2014.0402
Endovascular treatment of acute ischemic stroke: the end or just the beginning?
Authors: Mokin Maxim , Khalessi Alexander A. , Mocco J , Lanzino Giuseppe , Dumont Travis M. , Hanel Ricardo A. , Lopes Demetrius K. , Fessler Richard D. , Ringer Andrew J. , Bendok Bernard R. , Veznedaroglu Erol , Siddiqui Adnan H. , Hopkins L. Nelson , Levy Elad I.
Published: January 2014

Various endovascular intraarterial approaches are available for treating patients with acute ischemic stroke who present with severe neurological deficits. Three recent randomized trials—Interventional Management of Stroke (IMS) III, Mechanical Retrieval and Recanalization of Stroke Clots Using Embolectomy (MR RESCUE), and Synthesis Expansion: A Randomized Controlled Trial on Intra-Arterial Versus Intravenous Thrombolysis in Acute Ischemic Stroke (SYNTHESIS Expansion)—evaluated the efficacy of endovascular treatment of acute ischemic stroke and, after failing to demonstrate any significant clinical benefit of endovascular therapies, raised concerns and questions in the medical community regarding the future of endovascular treatment for acute ischemic stroke. In this paper, the authors review the evolution of endovascular treatment strategies for the treatment of acute stroke and provide their interpretation of findings and potential limitations of the three recently published randomized trials. The authors discuss the advantage of stent-retriever technology over earlier endovascular approaches and review the current status and future directions of endovascular acute stroke studies based on lessons learned from previous trials.
Imaging of high-risk carotid artery plaques: current status and future directions
Authors: DeMarco J. Kevin , Huston John
Published: January 2014

In this paper, the authors review the definition of high-risk plaque as developed by experienced researchers in atherosclerosis, including pathologists, clinicians, molecular biologists, and imaging scientists. Current concepts of vulnerable plaque are based on histological studies of coronary and carotid artery plaque as well as natural history studies and include the presence of a lipid-rich necrotic core with an overlying thin fibrous cap, plaque inflammation, fissured plaque, and intraplaque hemorrhage. The extension of these histologically identified high-risk carotid plaque features to human in vivo MRI is reviewed as well. The authors also assess the ability of in vivo MRI to depict these vulnerable carotid plaque features. Next, the ability of these MRI-demonstrated high-risk carotid plaque features to predict the risk of ipsilateral carotid thromboembolic events is reviewed and compared with the risk assessment provided by simple carotid artery stenosis measurements. Lastly, future directions of high-risk carotid plaque MRI are discussed, including the potential for increased clinical availability and more automated analysis of carotid plaque MRI. The ultimate goal of high-risk plaque imaging is to design and run future multicenter trials using carotid plaque MRI to guide individual patient selection and decisions about optimal atherosclerotic treatment strategies.
Asymptomatic carotid artery stenosis: time to rethink our therapeutic options?
Authors: Morales-Valero Saul F. , Lanzino Giuseppe
Published: January 2014

Asymptomatic carotid artery stenosis is a well-recognized risk factor for ischemic stroke, and its prevalence increases with age. In the late 1980s and in the 1990s, well-designed randomized trials established a definite advantage for carotid endarterectomy in reducing the risk of ipsilateral stroke when compared with medical therapy alone. However, medical treatment of cardiovascular disease has improved significantly over the past 2 decades, and this has, in turn, resulted in a decline of the stroke risk in patients with asymptomatic carotid artery stenosis treated medically. This improvement in medical therapy casts doubts on the effectiveness of large-scale invasive treatment in patients with asymptomatic carotid artery stenosis. Several studies have been conducted to identify possible subgroups of patients with asymptomatic stenosis who are at higher risk of stroke in order to maximize the potential benefits of invasive treatment. Ongoing large-scale trials comparing best current medical therapy to available invasive treatments, such as carotid endarterectomy and carotid artery stenting, are likely to shed some light on this debated topic in the near future. In this review, the authors summarize the current controversy surrounding the ideal management of asymptomatic carotid artery stenosis.