bluuebunny/crossref_metadata_2025 huggingface dataset:
Implementation of Real Time Geosteering to optimize horizontal drilling, greater Burgan field
Authors: Al-Zuabi Abdullah , Bahman Hussain , Al Zankawi Omran , Kotecha Rohit , Mereno Beltran , Mukherjee Pradeep , Mudavakkat Anandan , Al-Sabea Salem , Al-Hamoud Jamal
Published: May 2016

With increasing complexity to tap oil in clastic reservoirs due to stratigraphy, structure and facies variation optimization of placement of horizontal well has become a key to success. To augment this aspect Kuwait Oil Company (KOC) has established Geosteering Centre which has become the hub for decision making while the well is getting drilled for landing at top of reservoir or lateral is being drilled.

The Great Burgan field located in South East Kuwait asset of KOC major Horizontal drilling campaign started in 2005 mostly in clastic reservoirs.. This field been on the production since 70 years, most of its development wells were drilled and completed as vertical or deviated. It was decided to utilize horizontal well technology to drill thin productive layers. This paper illustrates an integrated approach using 3D-Model along with seismic analysis, knowledge sharing and most advanced Geosteering technology to successfully transfer, edit, and interpret the dynamic data in real time to monitor the drilling progress specially the lateral section. This state-of-the-art computing and visualization technology enables geologists to take corrective measures keeping the well in sweet zone as much as possible, through direct satellite communication with the rig's Geosteering unit and planned well course VS actual trajectory was continually updated and well path corrected based on information received.

The Geosteer center moved Field Development South-East Kuwait to a whole new level of collaboration that is equipped with latest in visualization, communication and computer technology in order to properly place and geologically navigate one of the world's largest siliciclastic reservoirs.

Today the interactive process of geosteering, using real-time data and making real-time decision has resulted in mitigating inherent geological risk in order to optimize the best drilling results for each horizontal well and to ensure an effective implementation of all new ongoing field development plans and made it possible to tackle thin reservoirs which now can be drilled economically.

Introduction

Kuwait oil Company initiated horizontal drilling approach since early 1990's, and to place the wells successfully in the desired reservoir, an integrated approach using static model and subsurface analysis, knowledge sharing, effective communications and state of the art geosteering technology have all been utilized in order to have a successful well placement.
Gas Oil Ratio (GOR) Estimation Using Downhole and Surface Well Sensors
Authors: Al Muailu Husain Al , Al Khelaiwi Faisal , Al Fakher Ahmad
Published: May 2016

As the concept of intelligent fields mature, field operators expand on the installation and utilization of downhole instrumentation in a quest for higher oil and gas recovery and net present value. Permanent downhole monitoring systems (PDHMS) are some of the intelligent field implementation enablers, which provide continuous monitoring and surveillance of wellbore/reservoir performance in addition to their recognized operational safety enhancement through elimination of well intervention operations for data acquisition. The advanced analysis of the data provided by this equipment forms the key to unlocking their full utilization potential and recognizing the value of the information that they provide.

A remote field located in Saudi Arabia commenced its production from a thin oil column lying between a large gas-cap and a water aquifer. The gas-cap gas breakthrough and production from the producing wells have increased gradually; resulting in an increase in the wells gas-oil ratio (GOR) from an average of 880 standard cubic ft/stock tank barrel (SCF/STB) at the start of the field production to 1,536 SCF/STB. The production of these wells is currently controlled using the surface and subsurface control valves to maintain the gas production and GOR at acceptable levels.

The wells connected to rate testing facilities are delivering non-accurate gas rate measurements because of frequent malfunctioning in the Coriolis meters. This problem is being mitigated in several fronts such as replacing the testing facilities; however, a method to estimate the GOR in the wells is needed until all the old testing facilities are replaced.

An innovative technique to identify the onset of gas-cap-gas production and estimate its value using the downhole sensors has been developed to provide early notification of the free gas breakthrough and improve its control. This technique can provide an estimation of the wells' GORs and can be used as a validation method to the testing facility GOR measurements.

This paper proposes an approach to estimate the GOR using Matlab code that helps in the calculation of the pressure drop between the PDHMS and matching it with the actual readings at the estimated GOR. This technique was tested on three wells with healthy rate and PDHMS information.
Transforming Seismic Reflection Data Into Quantitative Rock Properties by Seismic Inversion
Authors: Rajput Sanjeev
Published: May 2016

The transformation of seismic reflection data into quantitative rock properties can be very valuable in all phases of oil and gas exploration and production. In this study, public domain data from Australian offshore have been used to explain the logical workflow, which consists of systematic steps from seismic petrophysics to rock physics modeling and seismic inversion for quantitative rock property estimation.

The application of seismic inversion technology offers many rewards, such as: better reservoir definition and management; better resource estimation; and reductions in uncertainty. The main benefit is that it improves direct and intangible interpretation of seismic data to provide meaningful geological boundaries in the subsurface.

In order to provide the reliable estimate of rock properties for reservoir modeling the workflow is tested rigorously and divided into three categories which are based on the basic inversion types. The results reveal that relative impedance inversion should be performed first, which then followed by revision of seismic interpretation on impedance data. Full bandwidth rock properties are estimated by deterministic inversion. The results can be improved by several iterations of well to seismic tie, wavelet estimation, and low frequency models. As resolution with accuracy has always been challenging, the stochastic inversion approach is trailered for reservoir characterization and high resolution rock properties have been predicted. This produces a number of possible rock property models, as well as litho facies models and the results can be optionally constrained by the well data. It can be concluded that, to some degree, stochastic inversion is able to overcome the limited seismic bandwidth by integrating the rock physics properties of different lithologies. The examples of seismic inversion are discussed to demonstrate the significant benefits can be obtained by following an optimized workflow that is tailored to deal with the uncertainties that impact the end product.

Introduction

Seismic surveys are routinely performed to gather information about the geology of hydrocarbon fields. Seismic data, even when it has relatively low resolutions, can still deliver a structural model for the reservoir. The availability and coverage area of the data provides valuable information to constrain the reservoir model. Geophysicists are now able to extract greater quantitative information about reservoir rocks and fluid parameters from seismic data by working backwards using seismic inversion methods. Described as the flip-side of forward modeling, seismic inversion is the process of characterizing rocks and fluids that have produced the seismic data. In a sense, the process involves trying to determine the input (rock properties) by looking at the output (seismic data). It starts with actual measured data, removes the wavelet and derives acoustic impedance from reflection coefficient (Figure-1) with a low frequency model to infer rock properties and deliver earth model.
Basin-scale Simulators For De-risking Of Unconventional Play-types: A Practical Approach To Enable In-time Decision Support.
Authors: Keym Matthias , Meuric Olivier , Kuhn Philipp , Buerger Claudius , Dieckmann Volker , Podlaha Olaf , Senior William
Published: May 2016

Introduction

Unconventional resources have emerged as an important part of the world's energy supply. Engineering technological advances such as drilling horizontal clusters and completion solutions like hydraulic fracturing have contributed to the exponential growth of unconventional opportunities and their exploitation. Still a lot of headroom is left for a deep and improved understanding of the subsurface geologic controls on hydrocarbons' fluid movement and trapping characteristics. These characteristics are becoming paramount to de-risk the presence and extent of producible hydrocarbons in current and upcoming resource play opportunities.

Unconventional Basin Simulator technology

More specifically, it is the actual migration path and the compositional changes and alteration processes along it, which require an increase in focus. The latter seems to show a bigger impact than the initial question of whether a particular trap or reservoir was charged.
Applying 3D Close the Loop and Probabilistic Seismic Inversion Techniques on the Tibr Asset in Petroleum Development Oman
Authors: Scholten-Vissinga Marianne , Chockalingam Chuck , Tiller Gottfried M
Published: May 2016

In Petroleum Development Oman (PDO), a seismic driven 3D Close the Loop workflow has been successfully applied for the first time to the Tibr asset. The business objective was to delineate channel sands with challenging rock properties at a relatively deep target by better predicting the distribution of sands and shales within the Upper Gharif and Al Khlata reservoir sequences. As a result, we were able to reduce subsurface uncertainties leading to improved reserve estimates.

3D Close the Loop workflows allow for better predictions of layer thickness, reservoir properties and velocity away from the wellbore by optimal integration of seismic amplitudes with all other reservoir data. A pre-existing static reservoir model describing reservoir properties through geo-statistical algorithms served as main input. Rock and fluid property models were derived from existing well data. By relating reservoir properties such as net-to-gross, porosity and hydrocarbon saturation to acoustic properties, the 3D models were converted to a synthetic seismic volume, which could then be compared to measured seismic data. In the final stochastic inversion, reservoir properties were updated until synthetic and seismic data matched within an acceptable error range defined by the signal to noise ratio.
Optimizing Reservoir Testing Operations With Downhole Wireless Telemetry System
Authors: Acar Cagdas , Aljifri Abdullah , Bekkouche Yassine , Maalej Mohamed , Nwagbogu Ifeanyi , Vannuffelen Stephane
Published: May 2016

A new wireless telemetry system has been field tested in a variety of conditions in Middle East with excellent reliability. This wireless system enables bidirectional communication between the surface and downhole tools during testing operations by using acoustic signal. The wireless telemetry is used to transmit bottomhole pressure and temperature to the surface and permits control of downhole tools. This paper will describe the operating principle of the wireless system, present examples of how this system has been used to optimize the testing operations and summarize the key benefits achieved. The real time downhole data, compared with memory data has shown good match, has been streamed to client office successfully in real time, realized benefits from the operation and reservoir aspects for a vertical deep offshore well: Efficient management of wellbore events; providing operational awareness about tools status; refining the test sequences in real time, verifying underbalanced prior to perforation, monitoring stimulation pressures at sandface to avoid fracturing, updating the reservoir interpretation in real-time, optimizing the duration of flowing well sequences (clean up) and verifying the achievement of test objectives prior to retrieving DST string.

Introduction

Exploratory well testing to evaluate hydrocarbon bearing zones in new fields is normally performed with a drilling rig on location. The main objective of exploration well testing is to capture representative data on the reservoir and fluids by acquiring surface and downhole measurements in optimum time and cost manner. Wireless telemetry system that can transmit data from the bottom hole to the surface instead of solely relying on surface data and waiting for downhole sensor retrieval at the end of the test enables achieving this objective.

There are some systems in use in the industry while they are far from the efficiency due to following reasons: 1- Wireless System providers and overall downhole testing operations providers are different that usually brings the integration of the service issues 2- The Wireless System providers lack of the testing operation sequence and data flow 3- Wireless system providers do not have the testing real time capability and domain expertise that can upgrade the service level to solution level 4- The Available wireless telemetry systems within the main testing service providers has been limited to certain environments. Onshore and Low noise environments.
Step Change In Shallow Water Reflection Seismic By Advances In De-multiple Techniques
Authors: Roende H. , Huegen C. , Madsen L. , Emang M. I. , Halliday S. , Henderson J. R.
Published: May 2016

A high-resolution survey with a total of 2300 km2 of 3D reflection seismic data was acquired over the Al Shaheen Field, Block 5, offshore Qatar, from October 2006 to April 2007. Reverberations from the hard shallow water bottom and other types of noise limited the value of the original processing. Re-processing using new technologies has produced a step change in quality resulting in cleaner images for interpretation and superior angle stacks for inversion.

The multiples were removed by applying an enhanced processing workflow based on a predictive, data-driven algorithm. The workflow involved attenuating short-period water-layer related multiples - a process that is referred to as shallow water demultiple (SWD). The SWD method makes use of water-layer multiples in the data to reconstruct the missing water-bottom primary reflection, and then uses the reflection for predicting these shallow multiples. The method takes into account the spatial varying nature of the subsurface. Since the multiple model predicted by SWD has similar amplitude and phase as the input data, very short matching filters can be utilised in the adaptive subtraction process.

These processing improvements have influenced a broad spectrum of interpretations such as better structural representation including fault mapping and improved understanding of facies. In conclusion, detailed and careful testing has resulted in new added value from this large high resolution 3D data set by applying technologies that were not available when the data was acquired and processed in 2006–2008.

Introduction

Reflection seismic data is a primary tool for mapping the subsurface, structure and sedimentary facies and if the amplitudes are reliable, then also potentially lithology and fluid effects. The seismic signal is composed of the direct interface response, but is often contaminated by noise arising from multiples, scatter and mode conversions. This noise can make it difficult to interpret and analyse the seismic data. This paper presents a case study where an integrated approach between processing specialists and interpreters has successfully been adopted during the re-processing of a large 3D survey (2300 km2) acquired in 2006 and 2007 and where new technologies and workflows have made a step change in the quality of the 3D migrated cube. Demultiple, acquisition footprint removal and streamer/OBC merge have been improved to produce a volume that can be interpreted with higher confidence.
Reducing Drilling Risk using Look-ahead VSP – A Success Case Study for Carbonate Exploration Well, Offshore Vietnam
Authors: Nguyen Dac The , Sanders Michael , Millot Pascal , Rehman Sadu Ur , Jones Michael , Oo Aung Than , Golding Christopher James , Aquilina Giovanni , Fichera Rosario
Published: May 2016

The accurate prediction of the depth of top carbonate while drilling carbonate reservoirs is important to avoid losses and well control problems. This can have a significant financial impact. This paper demonstrates the use of innovative look-ahead VSP technology in Vietnam to refine depth prediction of the top of carbonate ahead of the bit for accurate geo-stopping.

An offshore exploration well was being drilled in an area with drilling challenges. This was the first well in the field and lacked offset well velocity information, so there was a high degree of depth uncertainty to the top of the carbonate target from surface seismic interpretations, making drilling operations risky. An intermediate VSP was requested to look for reflections ahead of the intermediate TD using Schlumberger VSI1 tool. The VSP data was acquired in open and cased hole using an air gun cluster as the seismic source.

The drilling program required the casing to be set immediately above the top of the carbonate. By acquiring an intermediate VSP, the depth uncertainty was reduced and the target depth prediction was refined. This was achieved using the look-ahead VSP technique, from which the acoustic impedance and velocity ahead of the bit was estimated. This was combined with time-depth from the VSP data over the logged interval to help refine the predicted depth to the top of the carbonate. This was used to optimize the depth at which the casing was set. The error range for the top carbonate depth from the surface seismic interpretation was +/-50m. The final prediction depth from the VSP interpretation is 6m shallower than the actual carbonate reservoir.

Guided by the inverted acoustic impedance log and velocity ahead of the bit from look-ahead VSP, a further 100m was safely drilled before setting the casing. The casing point was set successfully without penetrating the carbonate. The intermediate VSP results helped to decide drilling ahead in a safe manner with confidence, after setting the casing before penetrating the carbonate target.
Integrated Formation Evaluation Delivers an Optimum Exploitation Strategy in a Tight Sand Play, Offshore China
Authors: Shi R , Wang J , Zhang Guo Dong , Cai J , Tellapaneni Prasanna Kumar , Xian Chenggang , Chen Jichao , Yu Y
Published: May 2016

With increasing focus on exploration in tight and low-permeability environs, formation evaluation today has become more challenging. Integrating all measurements and understanding and evaluating uncertainties are critical for an effective evaluation workflow. Such a workflow should deliver the productivity and completion strategy for an effective exploitation of reserves. The field under study is an exploratory field located in the East China Sea, and the play is an anticline along a north-south axis. The main zone of interest is in a giant sandstone formation with very low porosity. Since this is a potentially large accumulation, it was necessary to produce gas to surface to confirm the discovery and book reserves.

In this study, an effective Reservoir Quality (RQ), Completion Quality (CQ) workflow is developed and executed to address the formation evaluation objectives in challenging environments. Integrating core measurements with petrophysical evaluation leads to an effective estimate of the petro physical properties and a quantitative estimate of the uncertainties involved. These uncertainties are then taken forward into a reservoir model to estimate the productivity from these sands. Geomechanical analysis is done to evaluate various completion options including hydraulic fracturing and an estimate of the post-fracturing productivity is evaluated for various fracturing scenarios. With this evaluation, an informed decision on the best way to exploit reserves was made. We present this study as an example of how various formation evaluation measurements can be integrated into a well deliverability workflow in a tight gas reservoir.

Introduction

The East China shelf basin offshore China is shown in Fig. 1. Although exploration has been ongoing in this basin since the early 1980s with some discoveries, mainly in the Chunxiao and Longjing structures (Jia and Ma 2000), given the size and complexity of the basin, exploration in this basin is still ongoing.
Demonstration of the Possibilities of Using a Phased Microphone Array as the Next-Generation Airport Noise Monitoring System
Authors: Chelliah Kanthasamy , Raman Ganesh , Aldeman Matthew R. , Patel Hirenkumar J.
Published: May 2016

Aircraft noise is a form of environmental noise pollution that is a cause for resident complaints, especially near larger airports. Noise monitoring is usually performed by placing single microphones at various locations in neighborhoods that are near airports. Single omnidirectional microphones, however, record every sound wave that is incident on the sensor. The sound amplitudes estimated by these single microphones include the contributions from environmental sources other than the aircraft, such as traffic noise, sirens, powered landscaping equipment, and barking dogs. Use of a phased array of microphones in combination with advanced beam-forming algorithms makes possible the selective monitoring of aircrafts’ localized sound amplitudes and thereby more accurately identifies aircraft-specific sound levels while minimizing the contributions from other sound sources. This paper demonstrates the noise source localization abilities of the phased-array system for the application of aircraft environmental noise monitoring.
Resilience Analytics of a Future Supply Chain for Aviation Biofuels
Authors: Connelly Elizabeth B. , Lambert James H.
Published: May 2016

Capacity-building plans for transportation systems must be resilient to disruptions and erroneous assumptions to protect performance outcomes as well as schedule and cost. An example is the future supply chain of aviation biofuels for industry, government, and military applications. The challenges include balancing the aims and assumptions of diverse stakeholders, including regulators, agencies, manufacturers, airlines, fuel companies, and agricultural and husbandry producers. Resilience analytics of the strategic plans should characterize both the influential trends and stressors and the robust initiatives. This paper demonstrates resilience analytics to address varied, evolving, and potentially conflicting stakeholder preferences in the life cycle of supply chains for aviation biofuels. Heterogeneous feedstocks can be converted to aviation biofuel, although several are more attractive across technological, environmental, and economic criteria. The choice of feedstocks for conversion to biofuel depends on balancing desired outcomes, including life-cycle costs, availabilities, proximities, environmental impacts, and the like. Resilience analytics enables prioritization of feedstocks and other supply chain initiatives, with prioritization that varies by scenario. A technology road map for near- and midterm investment horizons to establish aviation biofuels is described. Poultry waste products are explored by using the above methods for a particular region in the mid-Atlantic area of the United States.
Leveraging Worker Safety Perceptions to Promote Safe Performance in Airports: Investigating the Framing of Safety Standards and Worker Safety Construal
Authors: Keeney Jonathan E. , Hofmann David A.
Published: May 2016

Airports are complex systems characterized by unique and unpredictable safety challenges. Analyses of safety policies and practices focusing on organizational level (e.g., safety culture and climate) may overlook the importance of individual workers’ safety perceptions. The current research highlights two factors that play important roles in shaping these perceptions: the framing of safety standards and the level of abstraction with which workers conceptualize safety. From the perspective of the individual worker, operational safety is one of many workplace goals that must be balanced and prioritized. Workers are more likely to prioritize safety when safety standards are framed in negative (proscriptive) rather than positive (prescriptive) terms. Workers who tend to conceptualize safety in more abstract terms may prioritize safety appropriately when planning future behavior (i.e., during training) but give way to other considerations (e.g., schedule, cost) when faced with pressing decisions. Workers who view safety in very concrete terms, in contrast, are more attuned to the ethical implications of their choices (i.e., the potential for harm) and are therefore more likely to put safety considerations first. These arguments are supported by an empirical field study conducted in a large aviation services organization and shown to be robust to a variety of individual and organizational factors. Recommendations for airport managers indicate how these findings may be applied to enhance the efficacy of safety messages. Specifically, managers should present safety standards in negative terms; use vivid, concrete language when discussing safety; and continually reinforce the ethical implications of workplace safety.
Unaffordable Fare: Cost of Public Transportation for Low-Income Commuters Working at Chicago, Illinois, Midway International Airport
Authors: Nadeau Carey Anne
Published: May 2016

For airport employers, ensuring that the many low-income people employed as baggage handlers and retail salespeople, among others, can get to work ensures the continued efficient operations of the airport and the prosperity of the regional economy. However, high and increasing costs coupled with low wages make commutes unaffordable and constrain employees’ ability to get to their jobs. By using a case study of Chicago, Illinois, Midway International Airport, this research measures the extent to which low-income employees commuting to work at the airport by public transportation could afford their commute in 2011. The results of this analysis suggest that the cost of commuting on public transportation is beyond the means of a low-income budget. Furthermore, that fewer low-income commuters take public transportation as its affordability declines suggests that, although the availability and timeliness of public transportation favor low-income commuters compared with all commuters on average, the cost of public transportation may play a role in determining whether low-income commuters choose to work at the airport. These results promote interventions to increase affordability and expand accessibility to public transportation for low-income commuters to the airport.
Examining Aviation Navigation Display Symbology in Visual Search
Authors: Sivagnanasundaram Navaneethan , Palmer Evan , Chaparro Alex
Published: May 2016

This paper investigates properties of air traffic glyphs that may affect speed and accuracy when a navigation display is being searched. Four of these properties were explored: ( a) the amount of information represented, ( b) the number of aircraft displayed, ( c) the amount of information accessed, and ( d) the specific set of features representing the information. Two target detection experiments were conducted to measure speed and accuracy. Findings indicate that, generally, increases in the first three items negatively affect speed and accuracy. Furthermore, graphical features tend to be identified faster and more accurately than text-based features.
The Fundamental Role of Large-Scale Trust Building in Natural Resource Management
Authors: Marcus Karni
Published: May 2016

To better understand how to solve large-scale social dilemmas such as common-pool resource management, this paper provides a interdisciplinary critical analysis of scholarship to reveal the vicious cycle we are currently mired in. It proposes that current approaches to promote pro-environmental behaviour will be limited in their efficacy without a preliminary change in the level of trust among individuals and the systems that purport to support them. It then advances a new focus on large-scale trust building, suggesting paths for future research and a new direction for successful outcomes.
Governing Household Waste Management: An Empirical Analysis and Critique
Authors: Lougheed Scott Cameron , Hird Myra J. , Rowe Kerry R.
Published: May 2016

We conducted a survey of residents of Kingston, Ontario, Canada, (n = 107) to understand their attitudes to and experiences of waste management and governance. Currently, the municipality is emphasising waste diversion and exploring new waste processing systems (WPS; e.g., incineration) to reduce costs. Using Foucault's governmentality theory, our data suggest Kingston's reliance on an attitude-behaviour-context model of behaviour change successfully fosters an environmental citizenship identity based on waste diversion (e.g., recycling). However, we argue that the neoliberal governmentality upon which the attitude-behaviour-context model is predicated elides the need for, and inhibits consideration of, broader societal change concerning urgent environmental issues involving consumption and waste.
Geographic structuring and transgenerational maternal effects shape germination in native, but not introduced, populations of a widespread plant invader
Authors: Alba Christina , Moravcová Lenka , Pyšek Petr
Published: May 2016

PREMISE OF THE STUDY:

Germination is critical in determining species distributions and invasion dynamics. However, is it unclear how often invasive populations evolve germination characteristics different from native populations, because few studies have isolated genetic variation by using seed from garden‐grown plants. Additionally, while herbivore‐induced transgenerational effects are common, it is unknown whether maternal herbivory differentially shapes germination in native and introduced offspring.

METHODS:

We explored germination in native and introduced populations of the North American invader Verbascum thapsus using seed from garden‐grown maternal plants, half of which were protected from herbivores. To elucidate (1) germination niche breadth and (2) whether germination conditions affected expression of genetic structuring among populations, we germinated seed under four ecologically relevant temperature regimes.

KEY RESULTS:

Native populations had a wide germination niche breadth, germinating as well as or better than introduced populations. At cooler temperatures, native populations exhibited a genetically based environmental cline indicative of local adaptation, with populations from warmer locales germinating better than populations from cooler locales. However, this cline was obscured when maternal plants were attacked by herbivores, revealing that local stressors can override the expression of geographic structuring. Introduced populations did not exhibit clinal variation, suggesting its disruption during the introduction process.

CONCLUSIONS:

Native and introduced populations have evolved genetic differences in germination. The result of this difference manifests in a wider germination niche breadth in natives, suggesting that the invasive behavior of V. thapsus in North America is attributable to other factors.
Risk and Prognosis of Bacteremia and Fungemia among Peritoneal Dialysis Patients: A Population-Based Cohort Study
Authors: Dalgaard Lars Skov , Nørgaard Mette , Povlsen Johan Vestergaard , Jespersen Bente , Jensen-Fangel Søren , Ellermann-Eriksen Svend , Østergaard Lars , Schønheyder Henrik Carl , Søgaard Ole Schmeltz
Published: May 2016

Background

The incidence of bacteremia and fungemia (BAF) is largely unknown in end-stage renal disease (ESRD) patients initiating peritoneal dialysis (PD).

Objective

The main objective was to estimate and compare incidence rates of first episodes of BAF in incident PD patients and a comparison cohort. A secondary objective was to compare causative agents and 30-day post-BAF mortality between PD patients and the comparison cohort.

Methods

Design: Observational cohort study. Setting: Central and North Denmark regions. Participants: patients who initiated PD during 1995 – 2010. For each patient we sampled up to 10 controls from the general population matched on age, sex, and municipality.

Main outcome

Data on positive blood cultures were retrieved from electronic microbiology databases covering the 2 regions. We calculated incidence rates (IRs) of first-time BAF for PD patients and population controls. Incidence-rate ratios (IRRs) were calculated to compare these rates. Thirty-day mortality was estimated by Kaplan-Meier analysis.

Results

Among 1,024 PD patients and 10,215 population controls, we identified 75 and 282 episodes of BAF, respectively. Incidence rates of BAF were 4.7 (95% confidence interval [CI], 3.8 – 5.9) per 100 person-years of follow-up (PYFU) in PD patients and 0.5 (95% CI, 0.4 – 0.5) per 100 PYFU in population controls (IRR = 10.4; 95% CI, 8.1 – 13.5). In PD patients, the most frequent microorganisms were Escherichia coli (18.7%) and Staphylococcus aureus (13.3%). Escherichia coli (27.3%) also ranked first among population controls. Thirty-day mortality following BAF was 20.8% (95% CI, 12.6 – 31.0) and 20.7% (95% CI, 16.3 – 25.9) among PD patients and population controls, respectively.

Conclusions

Peritoneal dialysis patients are at markedly higher risk of BAF than population controls. Causative agents and the 30-day post-BAF mortality were similar in the 2 cohorts.
CORRELATIONS BETWEEN COMPOSITIONS AND ORBITS ESTABLISHED BY THE GIANT IMPACT ERA OF PLANET FORMATION
Authors: Dawson Rebekah I. , Lee Eve J. , Chiang Eugene
Published: May 2016

The giant impact phase of terrestrial planet formation establishes connections between super-Earths’ orbital properties (semimajor axis spacings, eccentricities, mutual inclinations) and interior compositions (the presence or absence of gaseous envelopes). Using N-body simulations and analytic arguments, we show that spacings derive not only from eccentricities, but also from inclinations. Flatter systems attain tighter spacings, a consequence of an eccentricity equilibrium between gravitational scatterings, which increase eccentricities, and mergers, which damp them. Dynamical friction by residual disk gas plays a critical role in regulating mergers and in damping inclinations and eccentricities. Systems with moderate gas damping and high solid surface density spawn gas-enveloped super-Earths with tight spacings, small eccentricities, and small inclinations. Systems in which super-Earths coagulate without as much ambient gas, in disks with low solid surface density, produce rocky planets with wider spacings, larger eccentricities, and larger mutual inclinations. A combination of both populations can reproduce the observed distributions of spacings, period ratios, transiting planet multiplicities, and transit duration ratios exhibited by Kepler super-Earths. The two populations, both formed in situ, also help to explain observed trends of eccentricity versus planet size, and bulk density versus method of mass measurement (radial velocities versus transit timing variations). Simplifications made in this study—including the limited time span of the simulations, and the approximate treatments of gas dynamical friction and gas depletion history—should be improved on in future work to enable a detailed quantitative comparison to the observations.
ON ULTRA-HIGH-ENERGY COSMIC RAYS AND THEIR RESULTANT GAMMA-RAYS
Authors: Gavish Eyal , Eichler David
Published: May 2016

The Fermi Large Area Telescope collaboration has recently reported on 50 months of measurements of the isotropic extragalactic gamma-ray background (EGRB) spectrum between 100 MeV and 820 GeV. Ultra-high-energy cosmic ray (UHECR) protons interact with the cosmic microwave background photons and produce cascade photons of energies 10 MeV–1 TeV that contribute to the EGRB flux. We examine seven possible evolution models for UHECRs and find that UHECR sources that evolve as the star formation rate (SFR), medium low luminosity active galactic nuclei type-1 (L = 1043.5 erg s−1 in the [0.5–2] KeV band), and BL Lacertae objects (BL Lacs) are the most acceptable given the constraints imposed by the observed EGRB. Other possibilities produce too much secondary γ-radiation. In all cases, the decaying dark matter (DM) contribution improves the fit at high energy, but the contribution of still unresolved blazars, which would leave the smallest role for decaying DM, may yet provide an alternative improvement. The possibility that the entire EGRB can be fitted with resolvable but not-yet-resolved blazars, as recently claimed by Ajello et al., would leave little room in the EGRB to accommodate γ-rays from extragalactic UHECR production, even for many source evolution rates that would otherwise be acceptable. We find that under the assumption of UHECRs being mostly protons, there is not enough room for producing extragalactic UHECRs with active galactic nucleus, gamma-ray burst, or even SFR source evolution. Sources that evolve as BL Lacs, on the other hand, would produce much less secondary γ-radiation and would remain a viable source of UHECRs, provided that they dominate.
THE BOLOCAM GALACTIC PLANE SURVEY. XIV. PHYSICAL PROPERTIES OF MASSIVE STARLESS AND STAR-FORMING CLUMPS
Authors: Svoboda Brian E. , Shirley Yancy L. , Battersby Cara , Rosolowsky Erik W. , Ginsburg Adam G. , Ellsworth-Bowers Timothy P. , Pestalozzi Michele R. , Dunham Miranda K. , Evans II Neal J. , Bally John , Glenn Jason
Published: May 2016

We sort 4683 molecular clouds between 10° < ℓ < 65° from the Bolocam Galactic Plane Survey based on observational diagnostics of star formation activity: compact 70 μm sources, mid-IR color-selected YSOs, H2O and CH3OH masers, and UCH ii regions. We also present a combined NH3-derived gas kinetic temperature and H2O maser catalog for 1788 clumps from our own GBT 100 m observations and from the literature. We identify a subsample of 2223 (47.5%) starless clump candidates (SCCs), the largest and most robust sample identified from a blind survey to date. Distributions of flux density, flux concentration, solid angle, kinetic temperature, column density, radius, and mass show strong (>1 dex) progressions when sorted by star formation indicator. The median SCC is marginally subvirial (α ∼ 0.7) with >75% of clumps with known distance being gravitationally bound (α < 2). These samples show a statistically significant increase in the median clump mass of ΔM ∼ 170–370 M
⊙ from the starless candidates to clumps associated with protostars. This trend could be due to (i) mass growth of the clumps at

M

˙

∼
200
–
440

M
⊙ Myr−1 for an average freefall 0.8 Myr timescale, (ii) a systematic factor of two increase in dust opacity from starless to protostellar phases, and/or (iii) a variation in the ratio of starless to protostellar clump lifetime that scales as ∼M
−0.4. By comparing to the observed number of CH3OH maser containing clumps, we estimate the phase lifetime of massive (M > 103
M
⊙) starless clumps to be 0.37 ± 0.08 Myr (M/103 M
⊙)−1; the majority (M < 450 M
⊙) have phase lifetimes longer than their average freefall time.
X-RAY SPECTRAL ANALYSIS OF THE STEADY STATES OF GRS1915+105
Authors: Peris Charith S. , Remillard Ronald A. , Steiner James F. , Vrtilek Saeqa D. , Varnière Peggy , Rodriguez Jerome , Pooley Guy
Published: May 2016

We report on the X-ray spectral behavior within the steady states of GRS1915+105. Our work is based on the full data set of the source obtained using the Proportional Counter Array (PCA) on the Rossi X-ray Timing Explorer (RXTE) and 15 GHz radio data obtained using the Ryle Telescope. The steady observations within the X-ray data set naturally separated into two regions in the color–color diagram and we refer to these regions as steady-soft and steady-hard. GRS1915+105 displays significant curvature in the coronal component in both the soft and hard data within the RXTE/PCA bandpass. A majority of the steady-soft observations displays a roughly constant inner disk radius (

), while the steady-hard observations display an evolving disk truncation which is correlated to the mass accretion rate through the disk. The disk flux and coronal flux are strongly correlated in steady-hard observations and very weakly correlated in the steady-soft observations. Within the steady-hard observations, we observe two particular circumstances when there are correlations between the coronal X-ray flux and the radio flux with log slopes

 and

. They are consistent with the upper and lower tracks of Gallo et al. (2012), respectively. A comparison of the model parameters to the state definitions shows that almost all of the steady-soft observations match the criteria of either a thermal or steep power-law state, while a large portion of the steady-hard observations match the hard-state criteria when the disk fraction constraint is neglected.
CONVECTIVE PROPERTIES OF ROTATING TWO-DIMENSIONAL CORE-COLLAPSE SUPERNOVA PROGENITORS
Authors: Chatzopoulos E. , Couch Sean M. , Arnett W. David , Timmes F. X.
Published: May 2016

We explore the effects of rotation on convective carbon, oxygen, and silicon shell burning during the late stages of evolution in a 20 M
⊙ star. Using the Modules for Experiments in Stellar Astrophysics we construct one-dimensional (1D) stellar models both with no rotation and with an initial rigid rotation of 50% of critical. At different points during the evolution, we map the 1D models into 2D and follow the multidimensional evolution using the FLASH compressible hydrodynamics code for many convective turnover times until a quasi-steady state is reached. We characterize the strength and scale of convective motions via decomposition of the momentum density into vector spherical harmonics. We find that rotation influences the total power in solenoidal modes, with a slightly larger impact for carbon and oxygen shell burning than for silicon shell burning. Including rotation in 1D stellar evolution models alters the structure of the star in a manner that has a significant impact on the character of multidimensional convection. Adding modest amounts of rotation to a stellar model that ignores rotation during the evolutionary stage, however, has little impact on the character of the resulting convection. Since the spatial scale and strength of convection present at the point of core collapse directly influence the supernova mechanism, our results suggest that rotation could play an important role in setting the stage for massive stellar explosions.
LOCAL ANALOGS FOR HIGH-REDSHIFT GALAXIES: RESEMBLING THE PHYSICAL CONDITIONS OF THE INTERSTELLAR MEDIUM IN HIGH-REDSHIFT GALAXIES
Authors: Bian Fuyan , Kewley Lisa J. , Dopita Michael A. , Juneau Stephanie
Published: May 2016

We present a sample of local analogs for high-redshift galaxies selected in the Sloan Digital Sky Survey (SDSS). The physical conditions of the interstellar medium (ISM) in these local analogs resemble those in high-redshift galaxies. These galaxies are selected based on their positions in the [O iii]/Hβ versus [N ii]/Hα nebular emission-line diagnostic diagram. We show that these local analogs share similar physical properties with high-redshift galaxies, including high specific star formation rates (sSFRs), flat UV continuums, and compact galaxy sizes. In particular, the ionization parameters and electron densities in these analogs are comparable to those in z ≃ 2–3 galaxies, but higher than those in normal SDSS galaxies by ≃0.6 dex and ≃0.9 dex, respectively. The mass–metallicity relation (MZR) in these local analogs shows −0.2 dex offset from that in SDSS star-forming galaxies at the low-mass end, which is consistent with the MZR of the

galaxies. We compare the local analogs in this study with those in other studies, including Lyman break analogs (LBA) and green pea (GP) galaxies. The analogs in this study share a similar star formation surface density with LBAs, but the ionization parameters and electron density in our analogs are higher than those in LBAs by factors of 1.5 and 3, respectively. The analogs in this study have comparable ionization parameters and electron densities to the GP galaxies, but our method can select galaxies in a wider redshift range. We find the high sSFR and SFR surface density can increase the electron density and ionization parameters, but still cannot fully explain the difference in ISM condition between nearby galaxies and the local analogs/high-redshift galaxies.
AN EXTERNAL SHOCK ORIGIN OF GRB 141028A
Authors: Burgess J. Michael , Bégué Damien , Ryde Felix , Omodei Nicola , Pe’er Asaf , Racusin J. L. , Cucchiara A.
Published: May 2016

The prompt emission of the long, smooth, and single-pulsed gamma-ray burst, GRB 141028A, is analyzed under the guise of an external shock model. First, we fit the γ-ray spectrum with a two-component photon model, namely, synchrotron+blackbody, and then fit the recovered evolution of the synchrotron νF

ν
peak to an analytic model derived considering the emission of a relativistic blast wave expanding into an external medium. The prediction of the model for the νF

ν
peak evolution matches well with the observations. We observe the blast wave transitioning into the deceleration phase. Furthermore, we assume the expansion of the blast wave to be nearly adiabatic, motivated by the low magnetic field deduced from the observations. This allows us to recover within an order of magnitude the flux density at the νF

ν
peak, which is remarkable considering the simplicity of the analytic model. Under this scenario we argue that the distinction between prompt and afterglow emission is superfluous as both early-time emission and late-time emission emanate from the same source. While the external shock model is clearly not a universal solution, this analysis opens the possibility that at least some fraction of GRBs can be explained with an external shock origin of their prompt phase.