bluuebunny/crossref_metadata_2025 huggingface dataset:
Governing by Managing Identity Boundaries: The Case of Family Businesses
Authors: Sundaramurthy Chamu , Kreiner Glen E.
Published: April 2008

In this paper we illustrate how boundary theory can be a useful perspective to understand the dynamics of family businesses. We integrate insights from the family business literature with the work–family and identity boundary literatures to describe degrees of integration between the family and business identities in family firms and outline contingencies that influence this integration. We also develop the notion of “differential permeability” as a state of being both integrated and segmented on various aspects of identity and articulate costs and benefits to this state, as well as to high integration and high segmentation. Finally, we invoke the research on “boundary work” as a means of managing family business boundaries and conclude by outlining additional avenues of research that stem from using such a boundary theory lens.
Effects of Radiofrequency Catheter Ablation on Myocardial Performance Index and Plasma NT‐Pro‐BNP Levels in Patients with Wolff‐Parkinson‐White Syndrome
Authors: Cakmak Nazmiye , Sayar Nurten , Cakmak Mahmut , Akyol Ahmet , Oguz Enis , Eksik Abdurrahman , Alper Ahmet Taha , Hasdemir Hakan , Yilmaz Hale , Erdinler Izzet
Published: April 2008

Background: The myocardial performance index (Tei index) is an echocardiographic index of combined systolic and diastolic functions. Brain natriuretic peptide (BNP) and its biologically inactive fragment N‐terminal pro‐BNP (NT‐pro‐BNP) are secreted by the heart in response to myocardial stretch. In this study, we investigated Tei index and NT‐pro‐BNP levels in patients with Wolff‐Parkinson‐White (WPW) syndrome before and after radiofrequency catheter ablation therapy (RFCA).

Methods: Thirty patients (19 males, 11 females, aged 35.5 ± 14.4 years) with WPW syndrome were enrolled in this study. Echocardiographic examination was performed before and 24 hours after RFCA. Tei index was calculated using Doppler echocardiography. Blood samples were taken before and 24 hours after RFCA to detect levels of NT‐pro‐BNP. Results: Although isovolumic contraction time (IVCT) and isovolumic relaxation time (IVRT) did not change, aortic ejection time (ET) was decreased after RFCA (276 ± 22 ms vs 254 ± 30 ms, P < 0.01). So Tei index was significantly higher in postablation period (0.36 ± 0.11 vs 0.42 ± 0.21, P < 0.05). NT‐pro‐BNP levels did not change significantly after RFCA. Conclusions: We demonstrated that restoration of normal atrioventricular conduction by RFCA, leads to increase in Tei index but does not effect plasma NT‐pro‐BNP levels.
Athletes' Heart and Echocardiography: Athletes' Heart
Authors: Stout Martin
Published: April 2008

Sudden death of competitive athletes is rare. However, they continue to have an impact on both the lay and medical communities. These deaths challenge the perception that trained athletes represent the healthiest segment of modern society. There is an increasing frequency of such reported deaths worldwide and the visibility of this issue is underlined by the high‐profile nature of each case. Differential diagnosis between pathological and the physiologic (nonpathological) responses to high levels of physical training has become clinically more important. The purpose of this review is to highlight the main echocardiograph characteristics related to different types of training/sports participation and to highlight already recognized and newer concepts in their clinical assessment.
Echocardiographic Diastolic Dysfunction and Magnetic Resonance Infarct Size in Healed Myocardial Infarction Treated with Primary Angioplasty
Authors: Barbieri Andrea , Bursi Francesca , Politi Luigi , Rossi Luca , Fiocchi Federica , Ligabue Guido , Pingitore Alessandro , Positano Vincenzo , Torricelli Pietro , Modena Maria Grazia
Published: April 2008

Background: After acute myocardial infarction (MI) the severity of diastolic dysfunction by echocardiography represents an independent prognostic marker. However, the mechanisms whereby diastolic dysfunction portends an increased risk after MI are not fully understood. We investigated the relationship between echocardiographic diastolic dysfunction severity and infarct size quantitatively measured by contrast‐enhanced magnetic resonance (ce‐MR). Methods: Cross‐sectional prospective study. We quantified “healed” infarct size by ce‐MR measuring the percentage of delayed enhancement with respect to left ventricular mass and diastolic function by Doppler echocardiography. Both exams were scheduled at least 1 month after a first acute ST segment elevation MI (STEMI) successfully treated with primary angioplasty and stenting. To increase the specificity, individual echocardiographic parameters were integrated to grade global diastolic function in 4 grades: normal diastolic function, impaired relaxation with normal, or near‐normal filling pressures; impaired relaxation with moderate elevation of filling pressures, and impaired relaxation with marked elevation of filling pressures, “restrictive filling.” Results: We prospectively enrolled 52 patients (mean age 62 ± 13 years, 77% men). ce‐MR and echocardiography were performed 48 ± 15 days after the MI. There was a significant but modest correlation between diastolic function grade and infarct size (r = 0.423, P = 0.002), which was independent of global and regional systolic function and persisted after further adjustment for age, sex, body surface area, left ventricular mass, end‐diastolic volumes, and sphericity index (all P < 0.05). Among single echocardiographic variables, infarct size correlated best with tissue Doppler velocities Em (r =−0.307, P = 0.03), Am (r =−0.39, P = 0.005), and flow propagation velocity (r =−0.34, P = 0.015). Conclusions: In healed STEMI successfully treated with primary angioplasty and stenting, diastolic function grade was independently albeit weakly correlated with infarct size. Therefore, the increased risk of diastolic dysfunction after MI is not fully explained by infarct size
Long‐Term (Up to 18 Years) Clinical and Echocardiographic Results of Mitral Balloon Valvuloplasty in Children in Comparison with Adult Population
Authors: FAWZY MOHAMED EID , STEFADOUROS MILTIADIS , AMRAOUI SOUAD EL , OSMAN ADIL , IBRAHIM IMAN , NOWAYHED OMAR , ELDALI ABDELMONEIM , CANVER CHARLES
Published: April 2008

Aims: The purpose of this study was to assess the safety, efficacy, and long‐term results (up to 18 years) of mitral balloon valvuloplasty (MBV) in children in comparison to adults.

Methods: 57 children age ≤ 18 years (group A) and 474 adult patients (group B) who underwent successful MBV and were followed up for a mean 8.5 ± 4.8 (range 1.5–18) years were analyzed.

Results: Patients in group A had a lower mitral echocardiographic score (echo score), 7.6 ± 1.3 vs. 8.1 ± 1 (P = 0.0005); smaller Doppler mitral valve area (MVA), 0.82 ± 0.16 cm2 vs. 0.92 ± 0.17 cm2 (P < 0.0001); and higher mitral valve gradient, 15.2 ± 2.3 mmHg vs. 14.3 ± 2.1 mmHg (P = 0.0003), than group B. Immediately after MBV, group A had larger MVA whether measured by catheter, 1.99 ± 0.57 cm2 vs. 1.8 ± 0.52 cm2 (P < 0.001), or by Doppler, 2.0 ± 0.27 cm2 vs. 1.97 ± 0.28 cm2 (P < 0.01), and similar complication rates, compared to group B. After a mean follow‐up of 8.5 ± 4.8 (range 1.5–18 years), restenosis in group A was 26% vs. 31% for group B (P = 0.41). Echo score > 8 (P = 0.046) was a predictor of restenosis in children and echo score > 8 (P < 0.0001) and previous surgery (P = 0.043) were predictors of restenosis in adults. Actuarial freedom from restenosis at 10, 15, and 18 years for groups A and B were 78%± 7%, 64%± 9%, and 18%± 14% and 77%± 2%, 43%± 4%, and 17%± 4%, respectively (P = 0.26). Event‐free survival rates at 10, 15, and 18 years were 87%± 6%, 62%± 1%, and 20%± 2% versus 87%± 1%, 51%± 4%, and 20%± 5% for groups A and B, respectively (P = 0.51). Postprocedure MVA < 2.0 cm2 (P = 0.043) and previous surgery (P = 0.03) were identified as predictors of events in children. Echo score > 8 (P < 0.0001) and prevalvuloplasty AF (P = 0.03) were identified as predictors of events in adults.

Conclusion: MBV is safe and effective in children with rheumatic MS. It provides better immediate results than in adults and excellent long‐term results that are comparable to those seen in adults.
Resuscitating the Microcirculation in Sepsis: The Central Role of Nitric Oxide, Emerging Concepts for Novel Therapies, and Challenges for Clinical Trials
Authors: Trzeciak Stephen , Cinel Ismail , Phillip Dellinger R. , Shapiro Nathan I. , Arnold Ryan C. , Parrillo Joseph E. , Hollenberg Steven M. ,   on behalf of the Microcirculatory Alterations in Resuscitation and Shock (MARS) Investigators
Published: April 2008

Microcirculatory dysfunction is a critical element of the pathogenesis of severe sepsis and septic shock. In this Bench‐to‐Bedside review, we present: 1) the central role of the microcirculation in the pathophysiology of sepsis; 2) new translational research techniques of in vivo video microscopy for assessment of microcirculatory flow in human subjects; 3) clinical investigations that reported associations between microcirculatory dysfunction and outcome in septic patients; 4) the potential role of novel agents to “rescue” the microcirculation in sepsis; 5) current challenges facing this emerging field of clinical investigation; and 6) a framework for the design of future clinical trials aimed to determine the impact of novel agents on microcirculatory flow and organ failure in patients with sepsis. We specifically focus this review on the central role and vital importance of the nitric oxide (NO) molecule in maintaining microcirculatory homeostasis and patency, especially when the microcirculation sustains an insult (as with sepsis). We also present the scientific rationale for clinical trials of exogenous NO administration to treat microcirculatory dysfunction and augment microcirculatory blood flow in early sepsis therapy.
Ridge alterations following immediate implant placement in the dog: flap versus flapless surgery
Authors: Blanco Juan , Nuñez Vanesa , Aracil Luis , Muñoz Fernando , Ramos Isabel
Published: April 2008

Objective: To assess the healing process after flap or flapless surgery in immediate implant placement.

Material and Methods: This study was carried out on five Beagle dogs. Four implants were placed in the lower jaw in each dog immediately after tooth extraction. Flap surgery was performed before the extraction on one side (control), and flapless on the contrary (test). After 3 months of healing, the dogs were sacrificed and prepared for histological analysis.

Results: Ten implants were placed in each group. Two failed (one of each group). The percentage of bone–implant contact was very similar in both groups: 64.8% and 65.1% for the flap and the flapless group, respectively. The difference between the mean distance from the peri‐implant mucosa margin to the first bone–implant contact at the buccal aspect was statistically significant between both groups (3.02 mm. flapless and 3.69 mm. flap group). The mean first bone–implant contact at the buccal aspect was located in relation to the sand‐blasted and acid‐etched level at 0.82 mm for the flapless group and 1.33 mm for the flap group. This difference was not statistically significant.

Conclusion: Flapless immediate implant surgery produces a significant reduction in the vestibular biologic width and a minor reduction in buccal bone plate resorption.
The challenge of dermatopathological diagnosis of composite tissue allograft rejection: a review
Authors: Kanitakis Jean
Published: April 2008

Advances in immunosuppressive treatments and microsurgical techniques have rendered allotransplantation of composite tissues (i.e. heterogeneous, non‐organ tissues) possible in humans. Most of these allografts (hands, face and abdominal wall) contain skin that may be the target of rejection, the diagnosis of which relies mainly on clinicopathological monitoring of the skin. Rejection of allografted skin manifests with changes that are characteristic but not very specific. Although composite tissue allografts are still in their infancy, they have opened a new era in the field of transplantation surgery and pathology, so that (dermato) pathologists may occasionally be faced with the challenge of diagnosing skin rejection of a composite tissue allograft. The diagnostic difficulties that may be encountered in the pathological evaluation of skin in this setting are discussed in this review.
A novel isoform of pantothenate synthetase in the Archaea
Authors: Ronconi Silvia , Jonczyk Rafal , Genschel Ulrich
Published: April 2008

The linear biosynthetic pathway leading from α‐ketoisovalerate to pantothenate (vitamin B5) and on to CoA comprises eight steps in the Bacteria and Eukaryota. Genes for up to six steps of this pathway can be identified by sequence homology in individual archaeal genomes. However, there are no archaeal homologs to known isoforms of pantothenate synthetase (PS) or pantothenate kinase. Using comparative genomics, we previously identified two conserved archaeal protein families as the best candidates for the missing steps. Here we report the characterization of the predicted PS gene from Methanosarcina mazei, which encodes a hypothetical protein (MM2281) with no obvious homologs outside its own family. When expressed in Escherichia coli, MM2281 partially complemented an auxotrophic mutant without PS activity. Purified recombinant MM2281 showed no PS activity on its own, but the enzyme enabled substantial synthesis of [14C]4′‐phosphopantothenate from [14C]β‐alanine, pantoate and ATP when coupled with E. coli pantothenate kinase. ADP, but not AMP, was detected as a coproduct of the coupled reaction. MM2281 also transferred the 14C‐label from [14C]β‐alanine to pantothenate in the presence of pantoate and ADP, presumably through isotope exchange. No exchange took place when pantoate was removed or ADP replaced with AMP. Our results indicate that MM2281 represents a novel type of PS that forms ADP and is strongly inhibited by its product pantothenate. These properties differ substantially from those of bacterial PS, and may explain why PS genes, in contrast to other pantothenate biosynthetic genes, were not exchanged horizontally between the Bacteria and Archaea.
Methodology of the Interventional Management of Stroke III Trial
Authors: Khatri Pooja , Hill Michael D. , Palesch Yuko Y. , Spilker Judith , Jauch Edward C. , Carrozzella Janice A. , Demchuk Andrew M. , Martin Renee‘ , Mauldin Patrick , Dillon Catherine , Ryckborst Karla J. , Janis Scott , Tomsick Thomas A. , Broderick Joseph P. ,   for the IMS III Investigators
Published: April 2008

Rationale

The Interventional Management of Stroke (IMS) I and II pilot trials demonstrated that the combined intravenous (i.v.) and intraarterial (i.a.) approach to recanalization may be more effective than standard i.v. rt-PA (Activase®) alone for moderate-to-large National Institutes of Health Stroke Scale (NIHSS ≥ 10) strokes, and with a similar safety profile.

Aims

The primary objective of this NIH-funded, Phase III, randomized, multicenter, open-label clinical trial is to determine whether a combined i.v./i.a. approach to recanalization is superior to standard i.v. rt-PA alone when initiated within 3 h of acute ischemic stroke onset. The IMS III trial will develop and maintain a network of interventional centers to test the safety, feasibility, and potential efficacy of new FDA-approved catheter devices as part of a combined i.v./i.a. approach to recanalization as the IMS III study progresses. A secondary objective of the IMS III trial is to determine the cost-effectiveness of the combined i.v./i.a. approach as compared with standard i.v. rt-PA. Trial enrollment began in July of 2006. Design A projected 900 subjects with moderate-to-large (NIHSS ≥ 10) ischemic strokes between ages 18 and 80 will be enrolled over the next 5 years at 40-plus centers in the United States and Canada. Patients must have i.v. treatment initiated within 3 h of stroke onset in both arms. Subjects will be randomized in a 2: 1 ratio with more subjects enrolled in the combined i.v./i.a. group. The i.v. rt-PA alone group will receive the standard full dose [0·9 mg/kg, 90 mg maximum (10% as bolus)] of rt-PA intravenously over an hour. The combined i.v./i.a. group will receive a lower dose of i.v. rt-PA (~0·6 mg/kg, 60 mg maximum) over 40 min, followed by immediate angiography. If a treatable thrombus is not demonstrated, no i.a. therapy will be administered. If an appropriate thrombus is identified, treatment will continue with either the Concentric Merci® thrombus-removal device, infusion of rt-PA and delivery of low-intensity ultrasound at the site of the occlusion via the EKOS® Micro-Infusion Catheter, or infusion of rt-PA via a standard microcatheter. If i.a. rt-Pa therapy is the chosen strategy, a maximum of 22 mg of i.a. rt-PA may be given. The choice of i.a. strategy will be made by the treating neurointerventionalist. The i.a. treatment must begin within 5 h and be completed within 7 h of stroke onset. Study outcomes The primary outcome measure is a favorable clinical outcome, defined as a modified Rankin Scale Score of 0–2 at 3 months. The primary safety measure is mortality at 3 months and symptomatic ICH within the 24 h of randomization.
Polypill: For Pollyanna*
Authors: Spence J. David
Published: April 2008

A single pill containing a statin, thiazide diuretic, β-blocker, angiotensin receptor antagonist, folate and ASA has been proposed for all people over age 55, with the aim of reducing cardiovascular disease by 80%. Unfortunately, there are insurmountable problems with choosing appropriate constituents of any such single remedy. Adverse effects, drug interactions, inter-individual variation in drug metabolism, and underlying causes of hypertension that differ between patients require individualized therapy. A single pill that will succeed in all patients is not only practically, but conceptually, an inappropriate approach for the prevention of cardiovascular disease.
Burden of Stroke in France
Authors: Leys Didier , Béjot Yannick , Debette Stéphanie , Giroud Maurice
Published: April 2008

France is a country of more than 60 million inhabitants, where indicators of health quality are favourable, with one of the longest life expectancies in the world, and one of the lowest rates of neonatal mortality. The burden of vascular diseases is smaller than in surrounding European countries of similar size (United Kingdom and Germany), even for stroke. However, the direct cost of health care provided to stroke patients is estimated between 2 and 2·5 billion Euros per year.
Impact of non‐alcoholic fatty liver disease on accelerated metabolic complications
Authors: FAN Jian Gao
Published: April 2008

Insulin resistance is the basis of both non‐alcoholic fatty liver disease (NAFLD) and metabolic syndrome (MetS), the two conditions are often found in the same individual. The mortality of patients with NAFLD is significantly higher than that among the general population and cardiovascular risk may compete with liver‐related risk in dictating the final outcome. Recent prospective studies have reported that NAFLD is associated with an increased incidence of MetS and type 2 diabetes mellitus, independent of obesity and other components of MetS. Thus, NAFLD may not only be a liver disease but also an early mediator of type 2 diabetes mellitus and MetS. The biological mechanisms by which NAFLD contributes to a higher risk of developing metabolic disorders are not fully understood. However, the fatty liver could contribute in the same way as visceral adipose tissue to insulin resistance, systemic inflammation and oxidative stress, while the decreased serum adiponectin concentrations might also be part of the mechanism. In contemporary clinical practice, it has become mandatory to evaluate the metabolic risk factors in NAFLD patients and to consider careful surveillance and aggressive treatment, not only of the resultant liver disease, but also of the possible underlying metabolic and vascular complications. Future studies might address the question whether earlier adjustment to a more efficient lifestyle or a pharmacological treatment that mobilizes fat out of the liver could reduce these risks.
Efficacy and safety of azathioprine maintenance therapy in a group of Crohn's disease patients in China
Authors: ZHENG Jia Ju , CHU Xing Qi , SHI Xiao Hua , ZHOU Chun Li , SENG Bi Wu
Published: April 2008

OBJECTIVE:  To evaluate the efficacy and the safety of long‐term azathioprine maintenance therapy in a group of Chinese patients with Crohn's disease.

METHODS:   The efficacy of azathioprine (2.0 mg/kg/day) in controlling the disease relapse in 13 patients with Crohn's disease following clinical remission by prednisone or surgery were investigated. The Crohn's disease activity index (CDAI) and the Harvey–Bradshaw index, the reduction of steroid dosage and side‐effects for an average of 18 months follow up were analyzed.

RESULTS:  Azathioprine was effective in controlling the disease relapse in 10 (by CDAI scores) or 11 (by Harvey –Bradshaw index) of 13 patients (76.9% and 84.6%, respectively) for at least 6 months. Azathioprine was not discontinued in a patient who experienced a temporary and mild elevation of aminotransferases 14 months after the initiation of therapy. However one patient who was co‐administered with azathioprine and mesalamine (Pentasa) developed an episode of bone marrow suppression that ultimately required the withdrawal of both medications.

CONCLUSION:  Azathioprine is an effective agent which controls the relapse of Crohn's disease in most patients. Long‐term remission can be achieved. Side‐effects, including severe leukopenia, myelo‐suppression and the mild elevation of hepatic enzymes, may occur in a small number of patients.
Discharge From the Edwards Aquifer Through the Leona River Floodplain, Uvalde, Texas1
Authors: Green Ronald T. , Winterle James R. , Prikryl James D.
Published: April 2008

Abstract:  Analysis of results from an electrical resistivity survey, a magnetic survey, and an aquifer test performed on the Leona River floodplain in south‐central Texas indicates that ground‐water discharge from the Edwards Aquifer through the Leona River floodplain may be as great as 91.7 Mm3/year. When combined with an estimate of 8.8 Mm3/year for surface flow in the Leona River, as much as 100.5 Mm3/year could be discharged from the Edwards Aquifer through the Leona River floodplain. A value of 11,200 acre‐ft/year (13.82 Mm3/year) has been used as the calibration target in existing ground‐water models for total discharge from Leona Springs and the Leona River. Including ground water or underflow discharge would significantly increase the calibration target in future models. This refinement would improve the conceptualization of ground‐water flow in the western portion of the San Antonio segment of the Edwards Aquifer and would thereby allow for more accurate assessment and management of the ground‐water resources provided by the Edwards Aquifer.
Descriptive study of perioperative transfusion practices in Spanish hospitals
Authors: BASORA MISERICORDIA , COLOMINA MARÍA J. , MORAL VICTORIA , LLAU JUAN V. , VILA MIGUEL , DURÁN LOURDES , SILVA SONSOLES , SÁNCHEZ CALIXTO A.
Published: April 2008

In order to identify opportunities to enhance blood‐sparing strategies, we studied blood‐transfusion practices in patients undergoing scheduled major surgery in Spain. This prospective, multicenter epidemiological study involved 20 Spanish hospitals. We recorded the pre‐ and postoperative hemoglobin concentrations, the estimated and calculated blood loss, the number of patients transfused and the blood‐sparing techniques used. A total of 359 patients from 18 centers were included in the analysis. Mean preoperative hemoglobin concentration was 13.7 ± 1.6 g/dL. In 29% of the patients, preoperative hemoglobin concentration was lower than 13 g/dL. All surgeries combined, mean estimated blood loss was 845 ± 659 mL and mean calculated blood loss 1722 ± 1021 mL. The percentage of patients transfused with allogeneic blood was 28.4% altogether and ranged from 47.2% in cardiac surgery patients to 4.5% in plastic‐maxillofacial surgery patients. Blood‐sparing techniques were used only in 70 patients (19.4%). For a large percentage patients who underwent scheduled major surgery, blood transfusion was needed and perioperative blood loss was underestimated. Blood‐sparing techniques were underused in non‐orthopedic surgery, despite the fact that sufficient time was available to plan appropriate blood‐sparing measures.
Optimal Performance and Geometry of Supersonic Ejector
Authors: Hewedy N. I. I. , Hamed Mofreh H. , Abou-Taleb F. Sh. , Ghonim Tarek A.
Published: April 2008

The optimum geometries of the ejectors, which give maximum efficiency, are numerically predicted and experimentally measured. The numerical investigation is based on flow equations governing turbulent, compressible, two-dimensional, steady, time averaged, and boundary layer equations. These equations are iteratively solved using finite-difference method under the conditions of different flow regimes, which can be divided into several distinctive regions where the methods for estimating the mixing length are different for each flow region. The first region depicts the wall boundary layer, jet shear layer, and secondary and primary potential flows. The second one contains a single region of developing flow. A simple ejector with convergent-divergent primary nozzle was fabricated and experimentally tested. The present theoretical and experimental results are well compared with published data. The results obtained are used to correlate the optimum ejector geometry, pressure ratio, and ejector optimum efficiency as functions of the operation parameters and ejector area ratio. The resultant correlations help us to select the optimum ejector geometry and its corresponding maximum efficiency for particular operating conditions.
Three-Dimensional Modeling of Hydraulic Fractures in Layered Media: Part II—Calibrations, Parametric Sensitivity and Field Simulations
Authors: Lee T. S. , Advani S. H. , Lee J. K.
Published: April 2008

A comprehensive finite element model formulation for the simulation of vertical hydraulic fracture propagation in a multi-layered reservoir has been presented in Part I of the companion paper (Advani et al., 1990). This paper presents a numerical calibration of this model by comparing results with selected benchmark cases. Parametric sensitivity investigations are also performed to illustrate the role of different variables on hydraulic fracture configuration evolution in multi-layered formations. In addition, field simulations for a multi-layered reservoir with differential in-situ stress and mechanical property contrasts are conducted to illustrate the scope of the developed model.
Experimental Study of Micronized Coal/Water Slurry Rheology at High Shear Rates
Authors: Cho Y. I. , Choi U. S.
Published: April 2008

The rheological behavior of four micronized coal water slurry (CWS) samples was studied experimentally for a wide range of shear rates between 3 and 30,000 s−1. The systematic rheological characterization of the slurry fuel shows that the rheological behavior of these CWS is very complex and depends on coal particle size, temperature, coal loading, conditioning additives, and the capillary tube diameter as well as the shear rate. This study indicates that better appreciation of the unique and complex rheological behavior of non-Newtonian CWS fuels is vital to developing high-quality slurries suitable for use in coal-fired diesel engines, and suggests that a more comprehensive data base for CWS rheology under actual diesel engine operating conditions is needed prior to using such CWS fuels in diesel engines.
Localized Deformation Using Higher Order Stress/Strain Theory
Authors: Koenders M. A.
Published: April 2008

A material is considered which consists of rough interacting blocks. The interaction, which is expressed in terms of the ratio of the normal and tangential force at the contact points of the blocks, is pure frictional if a certain maximal force ratio is reached, and elastic otherwise. The shape of the blocks is determined by the double shearing geometry. Failure modes for this material depend on the thickness of the slip band. The investigation is relevant to granular soils and rocks.
Self-Excited Vibrations Induced by Drag Bits
Authors: Dareing D. , Tlusty J. , Zamudio C.
Published: April 2008

Drillstring vibrations cause premature failure of downhole tools and the drillstring itself. Also, drill bits do not drill efficiently as a result of these vibrations and this inefficiency causes a significant reduction in penetration rate and a corresponding increase in footage cost. Drill bits are a primary source of excitation, but there has been no theory that adequately explains how drag bits excite drillstrings. The paper shows that these vibrations are self-excited by the interaction of drillstring, drill bit, and formation. The paper explains the mechanism for this self-excitation. Results show that drag bit design, shock absorber design and bit rotational speed dictate conditions of dynamic instability.
Response of Two-Degree-of-Freedom Rotating Machinery System With Quadratic Nonlinearity
Authors: Ertas A. , Anlas G.
Published: April 2008

A two-degree-of-freedom model of a rotating machine with nonlinear springs of quadratic type is studied. The multiple scales method is used to investigate the nonlinear oscillations of the forced system where the forcing is due to the eccentricity e of the rotor about its center of mass. The behavior of the system for the primary resonances Ω = ω1, Ω = ω2, and internal resonance ω2 = 2ω1 is analyzed. Other features, such as amplitude jump and saturation phenomenon, have been observed. The amplitudes versus detuning parameters for both cases are plotted. The critical values of mass ratios and spring ratios for the presence of an internal resonance are studied and interpreted for this particular application.
Temperature Variation in a Circulating Wellbore Fluid
Authors: Arnold F. C.
Published: April 2008

When a fluid is circulated in a wellbore, the temperature profile is determined by the transfer of heat from surrounding formations to the fluid. An analytical solution of the differential equations describing the transfer of heat has been developed. The solution assumes steady flow of heat in the wellbore and is coupled to the transient conduction of heat in the formation. The solution is validated by comparison to temperature measurements from the literature. A parametric study of the sensitivity to operating conditions is included.
Upper Ball Joint Force Variations due to Riser Tensioner and Vessel Motions—Part I: Derivation of General Equations
Authors: Kozik T. J. , Lowell J. E. , Ertas A.
Published: April 2008

General equation for the tensioner cable forces and for the forces exerted on the riser upper ball joint by the ship joint-tensioner system are derived. An analysis of the variation of forces acting on the upper ball joint of a riser string due to drill ship motion and riser tensioner dynamic has been conducted. The analysis includes the effect of breakaway torque on the tensioner sheaves while assuming vessel and upper ball joint motion to be independent.
Second Law Optimization of a Sensible Heat Thermal Energy Storage System With a Distributed Storage Element—Part 1: Development of the Analytical Model
Authors: Taylor M. J. , Krane R. J. , Parsons J. R.
Published: April 2008

This study explores the behavior of a flat-slab, sensible heat thermal energy storage system, the physical design and operation of which have been optimized to minimize the production of entropy by thermodynamic irreversibilities. Unlike many previous studies, the present work includes the entropy production by transient heat conduction within the storage element; that is, the analytical model is based on a distributed, as opposed to a lumped, storage element. The work is presented in two parts. The development of the analytical model required to compute the figure of merit, which is called the entropy generation number, in terms of the design and operational parameters of the system is presented in Part I. In Part II, the numerical solution of the analytical model is discussed and the results of an optimization study are presented and interpreted.
Second Law Optimization of a Sensible Heat Thermal Energy Storage System With a Distributed Storage Element—Part II: Presentation and Interpretation of Results
Authors: Taylor M. J. , Krane R. J. , Parsons J. R.
Published: April 2008

This study explores the behavior of a flat-slab, sensible heat thermal energy storage system, the physical design and operation of which have been optimized to minimize the production of entropy by thermodynamic irreversibilities. The analytical model is developed in Part I of this work. This part includes a description of the numerical model and the presentation and interpretation of the results of a system optimization study. The major results of this study show that: 1) any Second Law model of a thermal energy storage system must include a distributed storage element in order to make realistic estimates the thermodynamic performance of the system; 2) unconstrained optimization of the design of a thermal energy storage system tends to yield a system that is undesirably large, but by constraining the number of transfer units (NTU), it is possible to design systems of a realistic size without seriously degrading the thermodynamic performance; 3) counterflow systems operated without a dwell period are the most efficient type of system; and 4) the use of a dwell period with a counterflow system, or the operation of a system in parallel flow instead of counterflow, degrades the thermodynamic performance of the system and increases the required system size (NTU) in comparison to a counterflow system operated without a dwell period.
Fracture of an Orthotropic Strip Containing a Pair of Coplanar Cracks Perpendicular to the Edges of the Strip
Authors: Lin W. H. , Tsai Y. M.
Published: April 2008

The problem of an infinitely long orthotropic strip containing a pair of coplanar cracks perpendicular to the edges of the strip is studied. The surfaces of the cracks are loaded by an arbitrary pressure, while the edges of the strip are free from tractions. The solutions to the problem is written in terms of two potential functions. The mixed boundary value problem is reduced to a Fredholm integral equation of the second kind by using the techniques of Fourier transform and the finite Hilbert transform. In the special case of a uniform opening pressure, exact expressions for the stress intensity factors at the inner tips and the outer tips of the cracks as well as the shape of the deformed cracks are obtained. Numerical calculations for a fiber-reinforced composite are carried out to study the interaction between cracks, the existing stress-free edges, and the effect of the direction of the reinforcement fiber on the various quantities of interest in fracture mechanics. The cracks are either parallel or perpendicular to the reinforcement fiber.
A Simplified Analysis for Cold Storage in Porous Capsules With Solidification
Authors: Chen S. L. , Yue J. S.
Published: April 2008

This paper investigates the thermal performance of a cold storage system utilizing water porous capsules as phase change material. The proposed cold storage system can be used to shift electric demand from periods of high demand to ones of low demand. A simple lump model to determine the thermal characteristics has been developed. The solution of the system equations is found through the Laplace transformation method. Experimental data of temperature profiles obtained in this study for various porosities, coolant flow rates, and inlet coolant temperatures validate the theory. Effects of dimensionless parameters on the charge characteristics were found.
Tubular Bending and Pull-Out Forces in High-Curvature Well Bores
Authors: Dareing D. W. , Ahlers C. A.
Published: April 2008

This paper is concerned with drag forces developed on tubulars in high-curvature well bores typically found in drainhole and horizontal drilling. The dog-leg severity of these types of boreholes are considerably higher than those typically found in conventional directional drilling. The objective of the study was to determine the significance of bending stiffness on drag forces in the pull-out mode. The method of analysis treats the tubular as a multi-spanned curved beam under tension and solves for radial displacements, slope, shear and bending moment over each span. Calculations show that bending stiffness is a minor factor provided there are no locally severe dog legs superimposed in the high-curvature well bore.
Effect of Pipe Eccentricity on Surge Pressures
Authors: Haciislamoglu M. , Langlinais J.
Published: April 2008

This work is an analysis of non-Newtonian fluid flow in an annulus of any eccentricity with inner pipe motion, for typical petroleum drilling operations. The annular flow geometry and the two-dimensional laminar equation of motion are not approximations, but rather a finite difference method is used to develop a computer model which calculates the velocity profile and flow rate for a given frictional pressure loss. Very accurate velocity profiles of non-Newtonian (Bingham plastic and power law) fluids with inner pipe motion are obtained using exact geometries. Contour plots of the resulting velocity profiles in annuli of varying eccentricities help one visualize the effects of eccentricity as well as the effects of inner pipe movement and rheological properties of a fluid on surge pressures. Example cases show a significant reduction in surge pressure as eccentricity increases. The surge pressures are as much as 50 percent less than a concentric calculation when the inner pipe lays to one side of the hole. Therefore, previous concentric models are found to overpredict surge pressures in directional and horizontal wells. A correlation of frictional pressure is developed based on this model’s results. This correlation, permitting a quick calculation of surge pressures in eccentric annuli, can easily be incorporated into existing concentric models (steady state or unsteady state) to accurately calculate surge/swab pressures at any pipe eccentricity.
Ignition and Combustion of Liquid Fuel Droplet in a Convective Medium
Authors: Dash S. K. , Som S. K.
Published: April 2008

A mathematical model of droplet combustion in surroundings of hot gas with a uniform free stream motion is made from the numerical solution of the conservation equations of heat, mass and momentum in both the carrier and droplet phases. The gas phase chemical reaction between fuel vapor and oxidizer is assumed to be a single-step irreversible one. The phenomena of ignition is recognized by the sudden rise of temperature in the temperature-time histories at different locations in the carrier phase. The relative influences of pertinent input parameters, namely initial Reynolds number Rei, ratio of free stream to initial drop temperature T∞, and the ambient pressure on: (i) the ignition time lag, (ii) extinction characteristics, and (iii) life histories of burning fuel drops have been established.
Biaxial Characterization of Carbon/Epoxy Unidirectional and Quasi-Isotropic Composites
Authors: Mase G. T.
Published: April 2008

An experimental test program is described in which biaxial failure envelopes were generated for unidirectional [0]8 and quasi-isotropic [0/+45/90/−45]s specimens made from Toray T800HY/3910 graphite/epoxy. Data was generated in all four quadrants of the biaxial stress plane. Fiber direction failure strengths were also found by uniaxial tension and compression tests. The quasi-isotropic compressive failure strengths are approximately 50 percent of the tensile strengths. Failure strengths in the tension-tension quadrant were essentially the same as previous tubular specimen tests made of a similar material (Swanson and Christoforou, 1986) indicating that free-edge and stress concentration effects may not preclude using flat cruciform specimens to generate biaxial failure data.
High-Order Mixture Homogenization of Fiber-Reinforced Composites
Authors: Toledano A. , Murakami H.
Published: April 2008

An asymptotic mixture theory of fiber-reinforced composites with periodic microstructure is presented for rate-independent inelastic responses, such as elastoplastic deformation. Key elements are the modeling capability of simulating critical interaction across material interfaces and the inclusion of the kinetic energy of micro-displacements. The construction of the proposed mixture model, which is deterministic, instead of phenomenological, is accomplished by resorting to a variational approach. The principle of virtual work is used for total quantities to derive mixture equations of motion and boundary conditions, while Reissner’s mixed variational principle (1984, 1986), applied to the incremental boundary value problem yields consistent mixture constitutive relations. In order to assess the model accuracy, numerical experiments were conducted for static and dynamic loads. The prediction of the model in the time domain was obtained by an explicit finite element code. DYNA2D is used to furnish numerically exact data for the problems by discretizing the details of the microstructure. On the other hand, the model capability of predicting effective tangent moduli was tested by comparing results with NIKE2D. In all cases, good agreement was observed between the predicted and exact data for plastic, as well as elastic responses.
Upward Vertical Two-Phase Flow Through an Annulus—Part II: Modeling Bubble, Slug, and Annular Flow
Authors: Caetano E. F. , Shoham O. , Brill J. P.
Published: April 2008

Mechanistic models have been developed for each of the existing two-phase flow patterns in an annulus, namely bubble flow, dispersed bubble flow, slug flow, and annular flow. These models are based on two-phase flow physical phenomena and incorporate annulus characteristics such as casing and tubing diameters and degree of eccentricity. The models also apply the new predictive means for friction factor and Taylor bubble rise velocity presented in Part I. Given a set of flow conditions, the existing flow pattern in the system can be predicted. The developed models are applied next for predicting the flow behavior, including the average volumetric liquid holdup and the average total pressure gradient for the existing flow pattern. In general, good agreement was observed between the experimental data and model predictions.
The Effect of Waves on the Oil Slick at a Retention Boom
Authors: Kordyban E.
Published: April 2008

In the previous paper on this subject it was found that the oil-water interface at the retention boom becomes unstable under certain conditions permitting an oil escape under the boom. In the absence of waves, the experimental results were in fair agreement with predictions; but, when the waves were present, the instability occurred much earlier than predicted. In this paper the behavior of waves is studied both analytically and experimentally. It is found that the waves consist of a combination of stationary and progressive waves which is confirmed by the experiment, but the oil thickness variation on waves is found from experiment to be much greater than predicted. With certain modifications to the theory, the predicted onset of instability falls closely to experimental value.
Thermodynamic Optimization of Phase-Change Energy Storage Using Two or More Materials
Authors: Lim J. S. , Bejan A. , Kim J. H.
Published: April 2008

This paper documents the relative merits of using more than one type of phase-change material for energy storage. In the case of two phase-change systems in series, which are melted by the same stream of hot fluid, there exists an optimal melting point for each of the two materials. The first (upstream) system has the higher of the two melting points. The second part of the paper addresses the theoretical limit in which the melting point can vary continuously along the source stream, i.e., when an infinite number of different (and small) phase-change systems are being heated in series. It is shown that the performance of this scheme is equivalent to that which uses an optimum single phase-change material, in which the hot stream remains unmixed during the melting process. The time dependence, finite thickness and longitudinal variation of the melt layer caused by an unmixed stream are considered in the third part of the paper. It is shown that these features have a negligible effect on the optimal melting temperature, which is slightly higher than (T∞Te)1/2.
Application of Strain Space Plasticity Theory to Surface Strain Gage Measurements
Authors: Pattillo P. D. , Boswell R. S.
Published: April 2008

Taking strain as the independent variable, the strain space plasticity theory introduced by Naghdi and Trapp is applied to the problem of interpreting strain gage readings for load paths that involve inelastic deformation. Equations developed herein permit the straightforward decomposition of the total measured strain into elastic and plastic components. Further, the strain space formulation leads naturally to the prediction of stress components, both the strain decomposition and the stress calculation requiring information on uniaxial stress-strain behavior obtained from a simple tension test.
Multiple Shock Compaction of Simple Type Powders by Punch Impact
Authors: Sano Yukio
Published: April 2008

Recently, we have elucidated some mechanical behaviors of powders during the compaction. The elucidation involves the constitutive relations of a powder medium under the multishock compaction, the qualitative behavior such as the similarities of the compaction processes, the die wall friction effect, and the uniformity of the final density distribution of the compact with a high density, and the quantitative behavior analyzed by the pseudo-viscosity method and the shock fitting. This review describes this behavior systematically.
Pre-Combustion Removal of Carbon Dioxide From Natural Gas Power Plants and the Transition to Hydrogen Energy Systems
Authors: Mori Y. , Masutani S. M. , Nihous G. C. , Vega L. A. , Kinoshita C. M.
Published: April 2008

A system to reduce carbon dioxide emissions from combustion power plants is described. Unlike earlier proposals based on flue gas treatment, the problem is addressed prior to combustion by reforming the hydrocarbon fuel into H2 and CO2. Following separation, H2 is burned in place of the original fuel and the captured CO2 is liquefied and injected into the deep ocean at a depth sufficient to ensure effective containment, and to minimize damage to the marine environment. Calculations indicate moderate plant thermal efficiency and power cost penalties. In addition, the H2 production potential of this system may be exploited as a means to facilitate the transition from fossil fuels to future hydrogen energy systems.
Off-Diagonal Elastic Constants and Anisotropic Damage
Authors: Baste S. , Gerard A.
Published: April 2008

Various anisotropic damage models are investigated to take into account the nonlinear behavior of a ceramic matrix composite. A critical analysis of classical strain metrology results proves that it is unfeasible to evaluate the damage in a direction orthogonal to the stress one, because the nine elasticity constants of an orthotropic material are independent and Poisson’s ratios are strain’s second order, whereas Young’s modulus are first-order ones. An ultrasonic method provides the necessary stiffness variations, inaccessible by classical strain measurements, required to identify the anisotropic damage.