bluuebunny/crossref_metadata_2025 huggingface dataset:
Monitoring and Surveillance of Hemodialysis Vascular Access Using StenTec and Physical Exam
Authors: Dhamija Rajiv , Nash Shawn K. , Nguyen Shawn V. , Slack Kyle , Tadeo Joseph
Published: October 2014

Hemodialysis vascular access surveillance for hemodynamically significant stenosis can be a challenge because no universal gold standard exists. The StenTec Gauge measures static intra‐access peak pressure and graphically displays the ratio of this pressure to systemic systolic (peak) arterial pressure (PIA ratio). In combination with careful physical exam (PE), the StenTec Gauge is an acceptable and cost‐effective way of detecting hemodynamically significant stenosis in arteriovenous fistulas (AVF) or grafts (AVG). In a selected population of 21 hemodialysis patients with mature arteriovenous access, a StenTec reading and physical examination was measured on a weekly basis. Interventional procedures for suspected access dysfunction were performed if there was a greater than 25% increase of the PIA ratio from baseline in two consecutive readings, along with correlating clinical suspicion from physical examination findings. StenTec independently had a sensitivity of 56% and a specificity of 99% in detecting clinically significant stenosis. PE alone had a sensitivity of 89% and a specificity of 100%. StenTec combined with PE had a sensitivity of 100% and a specificity of 99% for predicting hemodynamically significant stenosis. StenTec detected 4 of 10 patients who had a PIA ratio value of ≥0.5, which correlates with current National Kidney Foundation Disease Outcomes Quality Initiative (KDOQI) criteria for mean intra‐access pressure ratios indicating a clinically significant outflow stenosis. PE predicted 9 of 10 patients with stenosis, and the combination of StenTec and PE predicted all 10 patients with clinically significant stenosis using the KDOQI criteria for PIA ratio. Hemodynamically significant access stenosis can be detected with excellent accuracy using both StenTec and PE measurements combined for monitoring and surveillance methods.
Factors associated with death from dengue in the state of Minas Gerais, Brazil: historical cohort study
Authors: Campos Kauara Brito , Amâncio Frederico Figueiredo , de Araújo Valdelaine Etelvina Miranda , Carneiro Mariângela
Published: October 2014

Objectives

To analyse the clinical and epidemiological profiles of dengue haemorrhagic fever (DHF), dengue shock syndrome (DSS) and complicated dengue cases and deaths from 2008 to 2010 that occurred in the state of Minas Gerais, south‐eastern Brazil, and to identify factors associated with death from dengue.

Methods

Historical cohort study using data from the Brazilian Information System for Notifiable Diseases. A descriptive analysis of the DHF, DSS and complicated dengue cases and deaths was performed; the incidence, mortality and case‐fatality rates were estimated. Logistic regression analysis was used to identify factors associated with death from dengue. Comorbidities were not included in the analysis because the information system does not contain such data.

Results

During the study period, 2214 DHF, DSS and complicated dengue cases were reported, including 156 deaths. The annual case‐fatality rates for DHF/DSS and complicated dengue cases in the period of 2008–2010 were 7.3%, 4.8% and 7.9%, respectively. The factors associated with death from dengue included residence in a municipality with a population of fewer than 100 000 inhabitants [odds ratio (OR) 2.46; 95% confidence interval (CI) 1.71–3.55], age over 65 years (OR 3.05; 95% CI 1.99–4.68) and plasma leakage (OR 1.69; 95% CI 1.16–2.46).

Conclusions

The results support the importance of plasma leakage as a warning sign associated with death from dengue as well as the signs and symptoms that allow the diagnosis of DHF. Moreover, our findings suggest that increased attention is necessary for individuals over 65 years of age and in municipalities with populations under 100 000 inhabitants to ensure a better quality of care during the management of severe patients of dengue in these locations. Differences in the interpretation of the DHF definition have hindered the comparison of data from different countries; it can improve from the WHO 2009 dengue classification.
Workplace‐based assessment: a new approach to existing tools
Authors: Parry‐Smith William , Mahmud Ayesha , Landau Alex , Hayes Kevin
Published: October 2014

Key content

Implementation of workplace‐based assessment (WPBA) has been fraught with difficulties and the RCOG is changing the assessments in light of these issues.

Current WPBA tools are principally formative assessments rather than summative assessments.

The distinction between formative assessment (for learning) and summative assessment (of learning) is crucial to understand the changes.

A revised approach to WPBA, with formative and summative encounters, is aimed at engaging both trainees and trainers.

Delivery of the changes to WPBA is the greatest challenge and the impact will need evaluation.

Learning objectives

To understand that WPBA entails the use of robust tools capable of capturing elements of clinical assessment and reflective practice.

To appreciate the role of WPBA within the assessment of clinical knowledge, skills and practice more widely.

To explore the new categorisation of WPBA tools currently used within O&G specialty training, informed by the principal objective of individual encounters

To appreciate that formative WPBA encounters will focus on the provision of structured, mandatory feedback whilst encouraging reflective practice by the trainee.

To understand that summative WPBA encounters will constitute assessments of observed performance, which allow trainees to demonstrate competence.

Ethics

Not applicable
Hormone therapy in survivors of gynaecological and breast cancer
Authors: Bregar Amy , Taylor Kristin , Stuckey Ashley
Published: October 2014

Key content

Gynaecological and breast cancers affect premenopausal and perimenopausal women at rates ranging 15–70% and treatment often causes the abrupt onset of menopause.

Available studies do not show an increase in recurrence or decrease in survival among women with endometrial, ovarian or cervical cancer who use hormone replacement therapy (HRT).

Data regarding the risks of systemic HRT in survivors of breast cancer are varied, and an increase in breast cancer recurrence with the use of systemic HRT has been demonstrated in randomised controlled trials. Limited data exist regarding the use of vaginal estrogen, however, no effect on recurrence has been demonstrated.

The decision regarding the use of HRT in women with cancer must be individualised and should take into account issues regarding quality of life.

Learning objectives

To review the evidence regarding the cancer‐specific risks, that is, recurrence or death, of HRT in survivors of gynaecological and breast cancer.

To provide recommendations for the use of HRT in survivors of gynaecological and breast cancer.

Ethical issues

How to balance the risks of HRT with quality of life concerns in survivors of gynaecological and breast cancer when evidence to guide our recommendations is limited?
Invoicing Currency in International Trade: An Empirical Investigation and Some Implications for the Renminbi
Authors: Lai Edwin L.‐C. , Yu Xiangrong
Published: October 2014

To play the role of a unit of account, an international currency must be a currency widely used to invoice international trade. This paper investigates the determinants of the use of currencies in trade invoicing and evaluates the potential of the renminbi for the denomination of cross‐border transactions in the Asia‐Pacific region. In particular, we develop a simple model and establish the evidence showing that there is a convex relationship between the invoicing share of a currency and the economic size of its issuing country because of a coalescing effect and thick market externalities. We use the ratio of the foreign exchange (FX) turnover share of a currency to the global GDP share of its issuing country as a proxy for the size of thick market externalities, which we argue reflects capital account openness, financial development and exchange rate stability of the country. This ratio is very small for the renminbi compared with the ratios for established international currencies. Our quantitative analysis suggests that the renminbi can be a major invoicing currency in the region only if China sufficiently opens up its capital account and liberalises its financial sector. We also draw a parallel between the renminbi and the euro and forecast the invoicing share of the renminbi in the Asia‐Pacific region if the renminbi market attained the same degree of thickness as the euro.
How are Exchange Rates Managed? Evidence of an Anchor‐Based Heuristic
Authors: Chen Kang , Kwan Chang Yee
Published: October 2014

Central banks often intervene in the foreign exchange market to obtain desirable exchange rates. How this is done has remained totally opaque although central banks are likely to adopt a satisficing rather than optimizing strategy as they need to intervene frequently in a timely manner under incomplete information. In this paper, we propose a simple exchange rate management rule that spreads the volatilities originated from the anchor currencies among the exchange rates with the domestic currency. We test out this rule on 10 currencies and find the empirical evidence consistent with the proposed anchor‐based heuristic.
Autonomic control of the heart: going beyond the classical neurotransmitters
Authors: Herring Neil
Published: October 2014

New Findings

What is the topic of this review?

This symposium report discusses the evidence for release of cardiac sympathetic cotransmitters in addition to noradrenaline.

What advances does it highlight?

It highlights the potential role of neuropeptide Y in reducing vagal neurotransmission and directly influencing ventricular myocyte excitability in the presence of β‐receptor blockade.

Acute myocardial infarction and congestive cardiac failure are characterized by high levels of cardiac sympathetic drive. In these conditions, sympathetic neurotransmitters such as neuropeptide Y (NPY) can be released in addition to noradrenaline, and plasma levels correlate with infarct size and mortality. Even in the presence of β‐blockers, NPY is able to bind to its own receptors located on cholinergic ganglia and ventricular myocytes. In this symposium report, I review the evidence that NPY can inhibit acetylcholine release during vagus nerve stimulation and limit the subsequent bradycardia. I also present preliminary, as yet unpublished data, demonstrating that NPY may be pro‐arrhythmic by directly influencing ventricular electrophysiology. Targeting NPY receptors pharmacologically may therefore be a useful therapeutic strategy both to reduce heart rate and to prevent arrhythmias in the setting of myocardial infarction and chronic heart failure. Such medications would be expected to act synergistically with β‐blockers, angiotensin‐converting enzyme inhibitors and implantable cardiac devices, such as defibrillators and vagus nerve stimulators.
Systemic oxidative–nitrosative–inflammatory stress during acute exercise in hypoxia; implications for microvascular oxygenation and aerobic capacity
Authors: Woodside John D. S. , Gutowski Mariusz , Fall Lewis , James Philip E. , McEneny Jane , Young Ian S. , Ogoh Shigehiko , Bailey Damian M.
Published: October 2014

New Findings

What is the central question of this study?

Exercise performance is limited during hypoxia by a critical reduction in cerebral and skeletal tissue oxygenation. To what extent an elevation in systemic free radical accumulation contributes to microvascular deoxygenation and the corresponding reduction in maximal aerobic capacity remains unknown.

What is the main finding and its importance?

We show that altered free radical metabolism is not a limiting factor for exercise performance in hypoxia, providing important insight into the fundamental mechanisms involved in the control of vascular oxygen transport.

Exercise performance in hypoxia may be limited by a critical reduction in cerebral and skeletal tissue oxygenation, although the underlying mechanisms remain unclear. We examined whether increased systemic free radical accumulation during hypoxia would be associated with elevated microvascular deoxygenation and reduced maximal aerobic capacity (). Eleven healthy men were randomly assigned single‐blind to an incremental semi‐recumbent cycling test to determine in both normoxia (21% O2) and hypoxia (12% O2) separated by a week. Continuous‐wave near‐infrared spectroscopy was employed to monitor concentration changes in oxy‐ and deoxyhaemoglobin in the left vastus lateralis muscle and frontal cerebral cortex. Antecubital venous blood samples were obtained at rest and at to determine oxidative (ascorbate radical by electron paramagnetic resonance spectroscopy), nitrosative (nitric oxide metabolites by ozone‐based chemiluminescence and 3‐nitrotyrosine by enzyme‐linked immunosorbent assay) and inflammatory stress biomarkers (soluble intercellular/vascular cell adhesion 1 molecules by enzyme‐linked immunosorbent assay). Hypoxia was associated with increased cerebral and muscle tissue deoxygenation and lower (P < 0.05 versus normoxia). Despite an exercise‐induced increase in oxidative–nitrosative–inflammatory stress, hypoxia per se did not have an additive effect (P > 0.05 versus normoxia). Consequently, we failed to observe correlations between any metabolic, haemodynamic and cardiorespiratory parameters (P > 0.05). Collectively, these findings suggest that altered free radical metabolism cannot explain the elevated microvascular deoxygenation and corresponding lower in hypoxia. Further research is required to determine whether free radicals when present in excess do indeed contribute to the premature termination of exercise in hypoxia.
Attenuated cerebral vasodilatory capacity in response to hypercapnia in college‐aged African Americans
Authors: Hurr Chansol , Kim Kiyoung , Harrison Michelle L. , Brothers R. Matthew
Published: October 2014

New Findings

What is the central question of this study?

The main purpose of this investigation is to determine whether there is a difference in cerebral vasodilatory capacity in response to rebreathing‐induced hypercapnia between African Americans and Caucasian Americans.

What is the main finding and its importance?

College‐aged African Americans have reduced cerebral vasodilatory capacity during hypercapnia when compared with Caucasian counterparts, a finding that suggests cerebral vascular dysfunction in this population. These findings may contribute to the understanding of the greater prevalence of cerebral vascular disease in this population.

African Americans (AAs) have increased risk for cardiovascular, cerebral vascular and metabolic disease, including hypertension, stroke, coronary artery disease, metabolic syndrome and type II diabetes, relative to Caucasian Americans (CAs). While it is accepted that endothelial function is impaired in AAs, less is known regarding their cerebral vasodilatory capacity in response to hypercapnia. We hypothesized that AAs have a reduction in the total range of change in cerebral blood flow velocity (CBFV) measured in the middle cerebral artery and an index of cerebral vascular conductance (CVCI) in response to changes in the partial pressure of end‐tidal carbon dioxide () during rebreathing‐induced hypercapnia when compared with CAs. Twenty‐one healthy, college‐aged AA (10 male) and 21 age‐ and sex‐matched CA (10 male) subjects participated in this study. A four‐parameter logistic regression was used for curve fitting the responses of CBFV and CVCI relative to changes in . The total ranges of change in CBFV (101 ± 18 versus 69 ± 23%; P < 0.001) and CVCI (83 ± 21 versus 58 ± 21%; P < 0.001) as well as the maximal increase in CBFV (205 ± 24 versus 169 ± 24%; P < 0.001) and CVCI (188 ± 30 versus 154 ± 19%; P < 0.001) were reduced during hypercapnia in AAs relative to CAs despite a similar increase in (change, 15 ± 3 versus 15 ± 3 mmHg; P = 0.65). In conclusion, these data indicate that AAs have attenuated cerebral vascular capacity to respond to hypercapnia when compared with CAs.
Experimental Study on High Damping Rubber Under Combined Action of Compression and Shear
Authors: Violaine Tinard , Quang Tam Nguyen , Christophe Fond
Published: October 2014

High damping rubber (HDR) is used in HDR bearings (HDRBs) which are dissipating devices in structural systems. These devices actually have to support permanent static load in compression and potential cyclic shear when earthquakes occur. Mastering the behavior of bearings implies an accurate understanding of HDR response in such configuration. The behavior of HDR is, however, complex due to the nonlinearity and time dependance of stress–strain response and especially Mullins effect. To the authors' knowledge, tests on HDR under combined quasi-static compression and cyclic shear (QC-CS) have not been performed with regard to Mullins effect yet. The purpose of this study is thus to assess experimentally Mullins effect in HDR, especially under QC-CS. In order to achieve this aim, cyclic tensile and compression tests were first carried out to confirm the occurrence of Mullins effect in the considered HDR. Then, an original biaxial setup allowing testing HDR specimen under QC-CS was developed. This setup enables us to identify Mullins effect of the considered HDR under this kind of loading. Tests carried out with this setup were thus widened to the study of the influence of compression stress on shear response under this loading, especially in terms of shear modulus and density of energy dissipation.
Scalable Fabrication of Low Elastic Modulus Polymeric Nanocarriers With Controlled Shapes for Diagnostics and Drug Delivery
Authors: Singh Vikramjit , Agarwal Rachit , Jurney Patrick , Marshall Kervin , Roy Krishnendu , Shi Li , Sreenivasan S.V.
Published: October 2014

A new process, decoupled functional imprint lithography (D-FIL), is presented for fabricating low elastic modulus polymeric nanocarriers possessing Young's modulus of bulk material as low as sub-1 MPa. This method is employed to fabricate sub-50 nm diameter cylinders with >3:1 aspect ratio and other challenging shapes from low elastic modulus polymers such as N-isopropylacrylamide (NIPAM) and poly(ethylene glycol) di-acrylate (PEGDA), possessing Young's modulus of bulk material <10 MPa which is cannot otherwise be imprinted in similar size and pitch using existing imprint techniques. Standard imprint lithography polymers have Young's modulus >1 GPa, and so these polymers used in nanocarrier fabrication in comparison have very low elastic modulus. Monodispersed, shape- and size-specific nanocarriers composed of NIPAM with material elastic modulus of <1 MPa have been fabricated and show thermal responsive behavior at the lower critical solubility temperature (LCST) of ∼32 °C. In addition, re-entrant shaped nanocarriers composed of PEGDA with elastic modulus <10 MPa are also fabricated. Nanocarriers fabricated from PEGDA are shown with model imaging agent and anticancer drug (Doxorubicin) encapsulated in as small as 50 nm cylindrical nanocarriers.
Conventional and Linear Statistical Moments Applied in Extreme Value Analysis of Non-Gaussian Response of Jack-Ups
Authors: do Nascimento Leonardo Sant'Anna , Sudati Sagrilo Luis Volnei , Ellwanger Gilberto Bruno
Published: October 2014

This work investigates numerically two different methods of moments applied to Hermite derived probability distribution model and variations of Weibull distribution fitted to the short-term time series peaks sample of stochastic response parameters of a simplified jack-up platform model which represents a source of high non-Gaussian responses. The main focus of the work is to compare the results of short-term extreme response statistics obtained by the so-called linear method of moments (L-moments) and the conventional method of moments using either Hermite or Weibull models as the distribution model for the peaks. A simplified mass-spring system representing a three-legged jack-up platform is initially employed in order to observe directly impacts of the linear method of moments (L-moments) in extreme analysis results. Afterward, the stochastic response of the three-legged jack-up platform is analyzed by means of 3D finite element model. Bias and statistical uncertainty in the estimated extreme statistics parameters are computed considering as the “theoretical” estimates those evaluated by fitting a Gumbel to a sample of episodical extreme values obtained from distinct short-term realizations (or simulations). Results show that the variability of the extreme results, as a function of the simulation length, determined by the linear method of moments (L-moments) is smaller than their corresponding ones derived from the conventional method of moments and the biases are more or less the same.
Thermal Properties of Silica Aerogel Formula
Authors: Cohen Ellann , Glicksman Leon
Published: October 2014

The thermal conductivity of silica aerogel developed in this research program was measured using the transient hot-wire technique. The thermal conductivity of monolithic samples drops significantly from 9.3 mW/m · K to 3.2 mW/m · K with modest pressure reduction from 1 atm to 0.1 atm. The same aerogel in granular form has a thermal conductivity of 15.0 mW/m · K at ambient gas pressure with a modest compression applied to compact the granules and reduce the air void sizes. Radiation heat transfer in the hot-wire test may not be representative of its contribution in large scale applications. Measurements of the monochromatic extinction coefficient over the wavelengths of interest resulted in a Rosseland mean extinction coefficient of 2400 m−1 at 300 K. The small thermal penetration distance during the hot-wire measurements suggest that in actual use radiation could contribute approximately 2.5 mW/m · K with a possible upper limit of 3.0 mW/m · K to the effective thermal conductivity over that measured using the transient hot-wire method.
Numerical Simulation and Parametric Study of Heat-Driven Self-Cooling of Electronic Devices
Authors: Kiflemariam Robel , Lin Cheng-Xian
Published: October 2014

A heat-driven self-cooling system could potentially utilize the heat dissipated from a device to power a thermo-electric generator (TEG) which could then provide power to run a cooling system. In this paper, numerical simulation and parametric analysis of the geometrical parameters (such as fin density and height) and system parameters are conducted to better understand the performance of the self-cooling system within wide ranges. The study showed further decrease in device temperature could be achieved by using shunt operation instead of direct contact between the device and the TEG module. The use of TEG cascades could also help improve the decrease in power generation as a result of shunt arrangement.
A Comparative Study of Shutdown Procedures on the Dynamic Responses of Wind Turbines
Authors: Jiang Zhiyu , Moan Torgeir , Gao Zhen
Published: October 2014

The shutdown of wind turbines may induce excessive loads on the structures and is an important factor to consider in their design. For pitch-regulated turbines, shutdown calls for blade pitching, and one- or two-blade shutdown may occur during pitch actuator failure. Through coupled analysis, this study investigated the dynamic responses of land-based and spar-type floating wind turbines (FWTs) during shutdown. We simulated the shutdown procedures by pitching one, two, or three blades, and by varying the pitch rate. The nonpitching blades have a fixed pitch angle during the process. Three generator torque conditions were considered: (1) grid loss, (2) mechanical braking, and (3) grid connection. The extreme response values and short-term and annual fatigue damages to the structural components were compared against these values under normal operation and parked conditions. Three-blade shutdown is recommended for both turbines. One- or two-blade shutdown with grid loss may result in a significant rotor overspeed and imbalanced loads acting on the rotor plane. Therefore, unfavorable structural responses are observed. Grid connection or mechanical braking alleviates the situation. The land-based turbine is more sensitive to the pitch rate when considering the tower bottom bending moment, but the blade moments and mooring line loads of the spar-type turbine are affected more.
Analysis of Static and Dynamic Characteristic of Hydrostatic Spherical Hinge
Authors: Xu Chundong , Jiang Shuyun
Published: October 2014

A new hydrostatic spherical hinge is developed in this paper to provide a large load capacity. The static and dynamic Reynolds equations in spherical coordinate system for incompressible Newtonian fluid were established using the perturbation method. Finite difference method was employed to solve the load capacity, power loss, oil flow rate, dynamic stiffness, and damping coefficients. This paper provides a new perspective for analysis on the dynamic characteristics of the spherical hinge.
Monte Carlo Simulation of Sunlight Transport in Solar Trees for Effective Sunlight Capture
Authors: Verma Navni N. , Mazumder Sandip
Published: October 2014

Solar photovoltaic (PV) cells arranged in complex 3D leaflike configurations—referred to as a solar tree—can potentially collect more sunlight than traditionally used flat configurations. It is hypothesized that this could be because of two reasons. First, the 3D space can be utilized to increase the overall surface area over which the sunlight may be captured. Second, as opposed to traditional flat panel configurations where the capture efficiency decreases dramatically for shallow angles of incidence, the capture efficiency of a solar tree is hampered little by shallow angles of incidence due to the 3D orientation of the solar leaves. In this paper, high fidelity Monte Carlo simulation of radiation transport is conducted to gain insight into whether the above hypotheses are true. The Monte Carlo simulations provide local radiation flux distributions in addition to global radiation flux summaries. The studies show that except for near-normal solar incidence angles, solar trees capture sunlight more effectively than flat panels—often by more than a factor of 5. The Monte Carlo results were also interpolated to construct a daily sunlight capture profile both for midwinter and midsummer for a typical North American city. During winter, the solar tree improved sunlight capture by 227%, while in summer the improvement manifested was 54%.
Modular Design and Experimental Testing of a 50 kWth Pressurized-Air Solar Receiver for Gas Turbines
Authors: Poživil Peter , Ettlin Nicolas , Stucker Fabian , Steinfeld Aldo
Published: October 2014

A high-temperature high-concentration pressurized-air solar receiver is considered for driving a power generation Brayton cycle. The modular design consists of a cylindrical SiC cavity surrounded by a concentric annular reticulated porous ceramic (RPC) foam contained in a stainless steel pressure vessel, with a secondary concentrator attached to its windowless aperture. Experimentation was carried out in a solar tower for up to 47 kW of concentrated solar radiative power input in the absolute pressure range of 2-6 bar. Peak outlet air temperatures exceeding 1200 °C were reached for an average solar concentration ratio of 2500 suns. A notable thermal efficiency—defined as the ratio of the enthalpy change of the air flow divided by the solar radiative power input through the aperture—of 91% was achieved at 700 °C and 4 bar.
Kinematics Meets Crystallography: The Concept of a Motion Space1
Authors: Chirikjian Gregory S.
Published: October 2014

In this paper, it is shown how rigid-body kinematics can be used to assist in determining the atomic structure of proteins and nucleic acids when using x-ray crystallography, which is a powerful method for structure determination. The importance of determining molecular structures for understanding biological processes and for the design of new drugs is well known. Phasing is a necessary step in determining the three-dimensional structure of molecules from x-ray diffraction patterns. A computational approach called molecular replacement (MR) is a well-established method for phasing of x-ray diffraction patterns for crystals composed of biological macromolecules. In MR, a search is performed over positions and orientations of a known biomolecular structure within a model of the crystallographic asymmetric unit, or, equivalently, multiple symmetry-related molecules in the crystallographic unit cell. Unlike the discrete space groups known to crystallographers and the continuous rigid-body motions known to kinematicians, the set of motions over which MR searches are performed does not form a group. Rather, it is a coset space of the group of continuous rigid-body motions, SE(3), with respect to the crystallographic space group of the crystal, which is a discrete subgroup of SE(3). Properties of these “motion spaces” (which are compact manifolds) are investigated here.
Numerical and Experimental Investigation of Aircraft Panel Deformations During Riveting Process
Authors: Abdelal Gasser F. , Georgiou Georgia , Cooper Jonathan , Robotham Antony , Levers Andrew , Lunt Peter
Published: October 2014

In collaboration with Airbus-UK, the dimensional growth of aircraft panels while being riveted with stiffeners is investigated. Small panels are used in this investigation. The stiffeners have been fastened to the panels with rivets and it has been observed that during this operation the panels expand in the longitudinal and transverse directions. It has been observed that the growth is variable and the challenge is to control the riveting process to minimize this variability. In this investigation, the assembly of the small panels and longitudinal stiffeners has been simulated using static stress and nonlinear explicit finite element models. The models have been validated against a limited set of experimental measurements; it was found that more accurate predictions of the riveting process are achieved using explicit finite element models. Yet, the static stress finite element model is more time efficient, and more practical to simulate hundreds of rivets and the stochastic nature of the process. Furthermore, through a series of numerical simulations and probabilistic analyses, the manufacturing process control parameters that influence panel growth have been identified. Alternative fastening approaches were examined and it was found that dimensional growth can be controlled by changing the design of the dies used for forming the rivets.
Laser-Machined Microchannel Effect on Microstructure and Oxide Formation of an Ultrasonically Processed Aluminum Alloy
Authors: Masurtschak S. , Friel R. J. , Gillner A. , Ryll J. , Harris R. A.
Published: October 2014

Ultrasonic consolidation (UC) has been proven to be a suitable method for fiber embedment into metal matrices. To aid successful embedment of high fiber volumes and to ensure their accurate positioning, research on producing microchannels in combination with adjacent shoulders formed by distribution of the melt onto unique UC sample surfaces with a fiber laser was carried out. This paper investigated the effect of the laser on the microstructure surrounding the channel within an Al 3003-H18 sample. The heat input and the extent of the heat-affected zone (HAZ) from one and multiple passes was examined. The paper explored the influence of air, as an assist gas, on the shoulders and possible oxide formation with regards to future bonding requirements during UC. The authors found that one laser pass resulted in a keyhole-shaped channel filled with a mixture of aluminum and oxides and a symmetrical HAZ surrounding the channel. Multiple passes resulted in the desired channel shape and a wide HAZ which appeared to be an eutectic microstructure. The distribution of molten material showed oxide formation all along the channel outline and especially within the shoulder.
High-Temperature Receiver Designs for Supercritical CO2 Closed-Loop Brayton Cycles
Authors: Ho C. K. , Conboy T. , Ortega J. , Afrin S. , Gray A. , Christian J. M. , Bandyopadyay S. , Kedare S. B. , Singh S. , Wani P.
Published: October 2014

High-temperature receiver designs for solar powered supercritical CO2 Brayton cycles that can produce ∼1 MW of electricity are being investigated. Advantages of a supercritical CO2 closed-loop Brayton cycle with recuperation include high efficiency (∼50%) and a small footprint relative to equivalent systems employing steam Rankine power cycles. Heating for the supercritical CO2 system occurs in a high-temperature solar receiver that can produce temperatures of at least 700 °C. Depending on whether the CO2 is heated directly or indirectly, the receiver may need to withstand pressures up to 20 MPa (200 bar). This paper reviews several high-temperature receiver designs that have been investigated as part of the SERIIUS program. Designs for direct heating of CO2 include volumetric receivers and tubular receivers, while designs for indirect heating include volumetric air receivers, molten-salt and liquid-metal tubular receivers, and falling particle receivers. Indirect receiver designs also allow storage of thermal energy for dispatchable electricity generation. Advantages and disadvantages of alternative designs are presented. Current results show that the most viable options include tubular receiver designs for direct and indirect heating of CO2 and falling particle receiver designs for indirect heating and storage.
Thermodynamic Analysis of the Ceria Redox Cycle With Methane-Driven Reduction for Solar Fuel Production
Authors: Krenzke Peter , Davidson Jane
Published: October 2014

The nonstoichiometric cerium oxide (ceria) redox cycle is an attractive pathway for storing energy from concentrated sunlight in chemical bonds by splitting water and carbon dioxide. The endothermic reduction reaction (R1)CeO2-δox→CeO2-δed+Δδ2O2 is favored thermodynamically at high temperatures and low oxygen partial pressures, while the CO2 and H2O splitting reactions (R2, R3) are exothermic and favored at lower temperatures and higher oxygen partial pressures. The produced hydrogen and carbon monoxide, referred to collectively as syngas, are important feedstocks used in the synthesis of ammonia and liquid fuels.(R2)CeO2-δed+ΔδCO2→CeO2-δox+ΔδCO   (R3)CeO2-δed+ΔδH2O→CeO2-δox+ΔδH2
Experimental Investigation of a Finned Mono Tube — Latent Heat Thermal Energy Storage (LHTES)
Authors: Urschitz Georg , Walter Heimo , Hameter Michael
Published: October 2014

The present experimental investigation covers the construction of a latent heat thermal energy storage system (LHTES), which uses sodium nitrate (NaNO3) as phase change material (PCM). The storage unit is filled with 300 kg of the PCM. For the heat transfer a vertically arranged bimetallic mono tube with longitudinal fins is used. The fins increase the heat flux into/from the PCM. Thermal oil is used as a heat transfer medium, as it allows working temperatures up to 400°C. This thermal energy storage is able to store 60 kWh of thermal energy and can be loaded with a power up to 200 kW. One part of the investigation results presented in this paper was the determination of the storable energy and the comparison with data from literature and calculations. Additionally, the melting behavior of the PCM was measured with temperature sensors located at different positions over the height of the storage unit. Finally, the entrance of the heat transfer medium was changed from the top to the bottom of the thermal energy storage unit and a different melting behavior could be detected.
Quantifying the Value of Concentrating Solar Power in a Production Cost Model
Authors: Jorgenson Jennie , Denholm Paul , Mehos Mark
Published: October 2014

While the levelized cost of energy (LCOE) is generally emphasized when assessing the economic viability of renewable energy systems, the other benefits such as the operational and capacity value are often ignored. Concentrating solar power with thermal energy storage (CSP-TES) can be dispatched similarly to conventional thermal generation, which may lead to incorrect economic comparisons between CSP-TES and variable renewable generation technologies such as wind and photovoltaics (PV). However, unlike most conventional thermal power plants, CSP-TES plants are energy limited, meaning that their response might be restricted by solar availability. Therefore, the use of this limited solar energy must be optimally scheduled to provide the greatest value to the power system. The timing of CSP-TES dispatch depends on a variety of factors, including electricity demand patterns, the penetration of variable generation sources, and the configuration of the CSP-TES plant itself. We use an established CSP-TES modeling framework in a commercially available production cost model to study the dispatch and value of a molten salt tower CSP-TES plant in a test system simulating the Colorado grid. We examine a range of configuration parameters by varying the relative sizes of three separate but interrelated parts of the CSP-TES plant: the solar collection field, the power block, and the thermal storage tank. Firstly, we observe that increasing the thermal energy storage capacity of a plant reduces spilled energy and increases the ability to deploy thermal energy to displace the most costly forms of conventional generation. Additional storage, however, shows only marginal benefit beyond 6–9 hours of rated plant capacity. Secondly, we observe that reducing the ratio of solar collection field size to power block capacity (a design parameter often called the solar multiple [SM]) provides the most benefit to this test system per unit of energy produced. A large solar collection field size, relative to the rated capacity of the power block, forces some solar energy to be stored during the periods when conventional generation is most costly. The stored solar energy must then be used during off-peak hours to displace less costly fossil generation. The relative value of CSP-TES presented here is dependent on many system variables, including existing solar energy penetration. Future work must examine the impact of capital cost on the overall value proposition of these configurations of CSP-TES, since the upfront cost is not considered here.
Effect of Thermal Storage on the Cooling Capacity of Ambient Sources
Authors: Robinson Brian S. , Sharp M. Keith
Published: October 2014

Ambient sources, including ambient air at dry-bulb and wet-bulb temperature, ground temperature and night sky temperature, were evaluated for their potential to provide space cooling in locations across the U.S. While ground temperature is constant beyond a certain depth, the other sources have fluctuating temperatures, which present intermittent potentials for cooling. Simultaneously, cooling demands also fluctuate with outdoor temperature. Thermal storage can bridge intervals of time during which cooling is needed in the building, but ambient source temperature is too high to provide cooling. The duration of these intervals and the thermal storage capacity required to meet cooling needs based on ambient source potential prior to the interval were quantified for all eleven climate zones across the continental U.S using TMY3 weather data. The thermal storage capacity required to meet the entire annual cooling load is dictated by the span of time without ambient source cooling potential that has the greatest ratio of cooling load to ambient source cooling potential prior to the interval. This maximum thermal storage capacity, normalized by building overall loss coefficient, (this ratio has units of time) was one day or less for night sky temperature for all but the three warmest climates. This ratio was one day or less for wet-bulb temperature for four locations, and for dry-bulb temperature for only two locations. Ground temperature provided continuous cooling potential in all but the three warmest climates, where ground temperature was warmer than the indoor comfort temperature. Because the maximum thermal storage capacity was determined in most climates by uncommon and infrequent coincidence of high cooling demand and low ambient source cooling potential, smaller thermal storage provided substantial cooling capacity in most cases. For instance, ten percent of the maximum supplied 99% of the cooling load for the dry-bulb ambient air source in Albuquerque, and 0.1% of the maximum served over 90% of the cooling load with night sky radiation in New Orleans and Phoenix. While considerable development of hardware and control algorithms to utilize ambient sources for space cooling has occurred, this study shows the potential of these sources to further reduce demands for conventional energy for space cooling across a wide range of climates.
Modeling of a High-Temperature-Serpentine External Tubular Receiver Using Supercritical CO2
Authors: Afrin Samia , Ortega Jesus D. , Ho Clifford K. , Kumar Vinod
Published: October 2014

This paper describes the modelling and design of an external receiver using supercritical CO2 as the heat transfer fluid that can reach up to 700 °C outlet temperature with ∼85% thermal efficiency. The internal pressure of the tubes is 20 MPa. The receiver tubes are arranged in a serpentine fashion and are coated with Pyromark 2500. Analyses were performed to evaluate the thermal efficiency of the receiver as a function of incidence angle of the incident radiation. Two different radiation models, discrete ordinates and surface-to-surface ray tracing, were used in the computational fluid dynamics model (ANSYS FLUENT). The receiver thermal efficiency ranged from 75% for incidence angles of 80 degrees to 88% for near-normal incidence angles of 10 degrees.
Active Modulated Reflectance Roofing System to Tailor Building Solar Loads for Increased HVAC Efficiency
Authors: Wolfe Daniel M. , Goossen Keith
Published: October 2014

Space heating and cooling contributes a significant percentage of a building’s overall energy usage profile. The construction of a building’s envelope is an essential component that impacts the overall heating and cooling load. For many years, flat roofs were covered with low albedo materials such as asphalt or modified bitumen, which can reach temperatures of 150°F to 180°F during summer months. More recently, alternative technologies, such as “white roofs”, have been put forth to mitigate the problem of unwanted thermal gain. However, these traditional roofing materials and recent innovations are passive structures and only promote seasonal benefits. This paper proposes and demonstrates the concept of an active variable reflectance roofing system that can tailor solar loads to desired heating or cooling, significantly reducing overall space heating and cooling energy requirements and costs.
Row House to Ranch House
Authors: Capen Judith , Capen Kirby
Published: October 2014

According to Lawrence Livermore Labs 36% of the country’s energy use is attributable to buildings and two thirds of that is in the residential sector.

This research combines building energy modeling with energy consumption data in transportation and infrastructure sectors to examine energy use implications of habitation patterns.

We compared CO2 footprints of three different patterns of typical American habitation: post-Second World War non-urban, 19th century urban, and highly urban. From drawings, utility bills, and occupant data, we used TREAT (Targeted Retrofit Energy Analysis Tool) to model the energy use of three buildings of very different constructions, comparing in the process the impact on energy use of envelope and size.

Because buildings don’t exist as isolated energy-using entities, we added the CO2 footprint contributions of location/density, reflected by infrastructure: numbers of miles of paving required to place a building in the landscape, miles of pipe for water and waste and the energy required by pumps to make it work.

Finally, people move between buildings, so we added a transportation component to account for occupants’ daily travel. Since buildings don’t use energy (people do) we divided total CO2 footprints by number of occupants for per capita CO2.

The final analysis quantifies the impact on an individual’s CO2 production of habitation (dense urban, historic urban, or non-urban) and how much impact energy conservation measures can have once the selection of a dwelling location is made.

Our analyses demonstrate that reduction of building energy use through improved construction affects only a small percentage of total energy usage.

Instead, choice of where to live determines individual CO2 footprints far more than building-related components. We found nearly a threefold difference in individual energy consumption from a New York City apartment dweller to a “close-in” suburban ranch house occupant with only minor differences between building-associated energy use. The bulk of the difference is attributable to differences in transportation utilization and infrastructure-related energy consumption.

Even as technical and legislative advances continue, our work demonstrates a broader societal dialogue about fundamental big picture issues, including sustainable densities, is critical.
Solid Phase Heat Recovery and Multi Chamber Reduction for Redox Cycles
Authors: Brendelberger Stefan , Felinks Jan , Roeb Martin , Sattler Christian
Published: October 2014

A system approach was used for the development of a new process concept for solar driven thermochemical redox cycles. Two aspects of this concept will be presented here. Since a high heat recovery rate for cycles using non-stoichiometric reduction has been identified as elementary in order to reach meaningful overall process efficiencies, a special focus was directed on this aspect. A quasi-countercurrent heat recovery system, which makes use of a particulate heat transfer medium, was outlined and numerically analyzed. The analysis shows that recovery rates of more than 70% seem realistic. Even though the heat recovery system is based on an arrangement of stages including relative complex flow pattern the basic principle seems promising and opens up new pathways for system design and optimization. The second aspect highlighted of the developed process concept is the use of a multi chamber system with optimized reaction conditions for the reduction of the redox material. By optimizing the pressure in a multi chamber system energy savings related to the pumping work of more than 20% are predicted. Also the execution of pre-reduction in the heat recovery system is discussed.
Design of a Micromix Fuel Injector for High Temperature Hybrid Concentrated Solar Power Plants
Authors: Coogan Shane , Brun Klaus , Teraji David
Published: October 2014

The hybrid air Brayton concentrated solar power plant (CSP) combines a natural gas fired combustor in series with a traditional CSP system. The combination boosts turbine inlet temperature above the receiver temperature and reduces output variability. However, a combustor operating in this mode must tolerate an inlet air temperature equal to the solar receiver outlet temperature, which is expected to be as much as 1,000°C for next generation designs. High inlet temperature hybrid combustors must achieve low NOx emissions in spite of the increased risk for autoignition and flashback. In addition, the hybrid injector must be able to adjust to the variability inherent to the solar source. The design of a multibank micromix injector that meets these challenges is described with emphasis on its NOx and CO emissions characteristics.