bluuebunny/crossref_metadata_2025 huggingface dataset:
Let's get ‘Fisical’ with bacterial nucleoid
Authors: Le Chat Ludovic , Espéli Olivier
Published: October 2012

The mechanisms driving bacterial chromosome segregation remain poorly characterized. While a number of factors influencing chromosome segregation have been described in recent years, none of them appeared to play an essential role in the process comparable to the eukaryotic centromere/spindle complex. The research community involved in bacterial chromosome was becoming familiar with the fact that bacteria have selected multiple redundant systems to ensure correct chromosome segregation. Over the past few years a new perspective came out that entropic forces generated by the confinement of the chromosome in the crowded nucleoid shell could be sufficient to segregate the chromosome. The segregating factors would only be required to create adequate conditions for entropy to do its job. In the article by Yazdi et al. () in this issue of Molecular Microbiology, this model was challenged experimentally in live Escherichia coli cells. A Fis–GFP fusion was used to follow nucleoid choreography and analyse it from a polymer physics perspective. Their results suggest strongly that E. coli nucleoids behave as self‐adherent polymers. Such a structuring and the specific segregation patterns observed do not support an entropic like segregation model. Are we back to the pre‐entropic era?
Permanent Pacing in Patients with Chagas' Disease
Authors: ARCE MAURICIO , VAN GRIEKEN JORGE , FEMENÍA FRANCISCO , ARRIETA MARTÍN , MCINTYRE WILLIAM F. , BARANCHUK ADRIAN
Published: October 2012

Background
:Chagas' disease is an endemic disease in most Latin American countries. The cardiomyopathy associated with this condition often requires permanent pacing due to bradycardia. The aim of this study was to compare the indications for pacemaker implantation, intraoperative measurements, and long‐term follow‐up of patients with Chagas' cardiomyopathy (ChCM) and ischemic cardiomyopathy (ICM) referred for pacemaker implantation.

Methods
: Retrospective study including consecutive patients with ChCM (Group 1) and ICM (Group 2), who underwent pacemaker implantation in a single center.

Results
: We analyzed 360 patients. Patients in Group 1 were younger (66.29 ± 7.01 vs 75.3 ± 7.11 years; P = 0.0001) and more often male (72% vs 60%; P = 0.05). Sinus node dysfunction (SND) was more prevalent in Group 1 (70% vs 52%; P = 0.03). Atrioventricular block was less prevalent in Group 1 (30% vs 48%; P = 0.04). No significant differences were found with respect to left ventricular ejection fraction (54.2 ± 9.1 vs 53.4 ± 8.2%; P = NS) and baseline QRS duration (119 ± 34 vs 108 ± 29 ms; P = NS). Right bundle branch block was more frequent in Group 1 (44% vs 12%; P = 0.0001), and left bundle branch block in Group 2 (6% vs 22%; P = 0.0001). Implantation time was longer in Group 1 (39 ± 19 vs 29 ± 13 minutes; P = 0.001) and was with higher atrial and ventricular pacing thresholds (1.4 ± 0.8 vs 1.0 ± 0.5 V; P = 0.001 and 1.2 ± 0.8 vs 0.6 ± 0.8 V; P = 0.001, respectively). During a follow‐up of 42.8 ± 13.6 months, Group 1 had a higher incidence of new atrial fibrillation (34% vs 25.5%; P = 0.001), and there was a nonsignificant trend toward more displacements of the ventricular lead (6% vs 3.5%; P = 0.3). There were no deaths during the follow‐up.

Conclusions
: ChCM patients receiving pacemakers are younger and more frequently have SND compared to those with ICM. Pacemaker implant is longer in patients with ChCM disease and is with higher pacing thresholds. The incidence of new atrial fibrillation during the follow‐up is significantly higher in patients with ChCM. (PACE 2012;35:1494‐1497)
Reduction of Procedure Duration and Radiation Exposure with a Dedicated Inner Lumen Mapping Catheter during Pulmonary Vein Cryoablation
Authors: PEYROL MICHAËL , SBRAGIA PASCAL , QUATRE AMANDINE , ORABONA MORGANE , CASALTA ANNE‐CLAIRE , BOCCARA GILLES , ZERROUK ZINEDINE , GUENOUN MAXIME , LÉVY SAMUEL , PAGANELLI FRANCK
Published: October 2012

Background

The Achieve catheter (AC; Medtronic‐CryoCath, Pointe‐Claire, Canada) is a circular mapping catheter introduced through the lumen of the cryoballoon (CB) catheter which is safe and effective to both navigate the CB to the pulmonary veins (PV) and allow PV potential recording during PV cryoablation. The aim of this study was to evaluate the impact of the use of the AC on procedural outcomes.

Methods

Sixteen consecutive patients (14 men) underwent AC‐guided PV isolation (PVI) for drug‐refractory paroxysmal atrial fibrillation (AF; AC group). Clinical and procedural data of these patients were compared to those obtained from 16 consecutive patients who had undergone PVI for paroxysmal AF with the regular “single transseptal” approach (control group).

Results

Clinical characteristics of patients enrolled in both groups did not differ significantly. In the AC group, 64 PVs were targeted using a single 28‐mm (n = 13) or 23‐mm (n = 3) CB catheter with PVI achieved in 62 PVs (97%). In the control group, 66 PVs were targeted using a single 28‐mm (n = 12) or 23‐mm (n = 4) CB catheter with PVI achieved in 62 PVs (94%), (P = non‐significant for CB size and PVI rate). Procedure duration and fluoroscopy time were significantly reduced in AC group compared to control group (96.6 ± 26 minutes vs 125.9 ± 25 minutes, P = 0.003 and 24.4 ± 10 minutes vs 32.6 ± 11 minutes, P = 0.04, respectively).

Conclusion

The use of the AC significantly reduced procedure duration and radiation exposure during PVI with the CB technique.

(PACE 2013; 36:24–30)
Long‐Term Follow‐up Impact of Dual‐Chamber Pacing on Patients with Hypertrophic Obstructive Cardiomyopathy
Authors: YUE‐CHENG HU , ZUO‐CHENG LI , XI‐MING LI , YUAN DAVID ZHE , DONG‐XIA JIN , YING‐YI ZHANG , HUI‐MING YANG , HONG‐LIANG CONG
Published: October 2012

Background

Pacing has been proposed as a treatment for patients with hypertrophic obstructive cardiomyopathy (HOCM), but there are few studies with long‐term follow‐up. We evaluated the long‐term effects of dual‐chamber pacing therapy for patients with HOCM, and to identify the most prognosis‐specific factors for predicting outcome in such treating methods.

Methods

A total of 37 HOCM patients implanted with dual‐chamber pacemakers were enrolled consecutively and followed‐up. Thirty‐seven cases were followed for 1 year, 26 cases for 2 years, 10 cases for 3 years, and eight cases for 4 years. At each annual point of follow‐up after pacemaker implantation, the pacing frequency, pacing threshold, impedance, atrioventricular delay, and cumulative percentage of atrial and ventricular pacing were tested, respectively. In addition, left atrial dimension (LAD), left ventricular end diastolic dimension (LVEDd), left ventricular posterior wall thickness (LVPW), interventricular septum thickness (IVS), left ventricular outflow tract dimension (LVOTd), peak velocity of left ventricular outflow tract (VLVOT), left ventricular outflow tract pressure gradient (LVOTPG), left ventricular ejection fraction (LVEF), and pulmonary artery systolic pressure (PASP) were measured. Mitral valve systolic anterior motion (SAM) was also observed. Pacing parameters and echocardiography indexes before and after pacemaker implantation were dynamically compared.

Results

Pacing frequency and atrioventricular delay were adjusted to 60–70 beats per minute and 90–180 ms, respectively, in order to ensure the ratio of ventricular pacing was more than 98%. Pacing threshold and pacing impedance were kept in normal ranges. The differences of various pacing parameters were of no statistical significance within the 4 years of follow‐up (P > 0.05). Compared with prior to pacing, it was observed that the IVS, VLVOT, and LVOTPG declined significantly (P < 0.01), the LVOTd widened significantly (P < 0.01), and the SAM phenomenon improved obviously (P < 0.01) at 1, 2, 3, and 4 years after pacemaker implantation. Additionally, the changes in LAD, LVEDd, LVPW, LVEF, and PASP were statistically insignificant (P > 0.05).

Conclusions

The cardiac structural reconstruction in patients with HOCM can be chronically improved by dual‐chamber pacing therapy. The IVS, LVOTd, VLVOT, and LVOTPG can be used as sensitive and specific factors in evaluating the long‐term effects of dual‐chamber pacing therapy for HOCM.

(PACE 2013; 36:86–93)
Comparative Determination and Monitoring of Biomarkers of Necrosis and Myocardial Remodeling between Radiofrequency Ablation and Cryoablation
Authors: HERNÁNDEZ‐ROMERO DIANA , MARÍN FRANCISCO , ROLDÁN VANESSA , PEÑAFIEL PABLO , VILCHEZ JUAN ANTONIO , ORENES‐PIÑERO ESTEBAN , GINER JOSÉ ANTONIO , VALDÉS MARIANO , GARCÍA‐ALBEROLA ARCADIO
Published: October 2012

Background

Biomarkers of necrosis and inflammation have been found raised after radiofrequency ablation (RF). There is scarce information on biomarkers’ behavior after cryoablation. Our aim was to study biomarkers of necrosis, inflammation, and interstitial remodeling after two different approaches: RF versus cryoablation.

Methods

We studied 22 consecutive patients with atrial flutter who underwent RF (10) or cryoablation (12). All patients underwent electrophysiological study and subsequent ablation. Peripheral samples were collected before the procedure, immediately after, the following day, 3 days, 1 week, 1 month, and 2 months after ablation. Samples were assayed for biomarkers of inflammation (high sensitive C‐reactive protein [hs‐CRP]) and tissue remodeling (C‐propeptide of type I procollagen [CICP], matrix metalloproteinase 2 [MMP‐2], matrix metalloproteinase 9 [MMP‐9], and metallopeptidase inhibitor 1 [TIMP‐1]). We also determined biomarkers of tissue necrosis (creatine kinase [CK], its MB isoenzyme, cardiac troponin I [TnI], and troponin T (TnT)] in samples obtained immediately after ablation, 6 hours postablation, and 12 hours postablation.

Results

Bidirectional isthmus block was achieved in all patients. We found significantly higher levels of CK, CK‐MB, and TnI after cryoablation compared to RF ablation for all timing samples. These necrosis biomarkers showed significant differences depending on the time (all P < 0.001), and the interaction between the time and the used ablation approach (P = 0.005, P < 0.001, and P < 0.001, respectively). For patients who undergoing RF ablation, MMP‐2 showed the greatest changes depending on the interaction between time and number of applications (P = 0.041), whereas for patients who undergoing cryoablation, CK was the most relevant biomarker depending on the interaction between time and number of applications (P = 0.006).

Conclusions

We show higher levels of necrosis and myocardial injury biomarker after cryoablation versus RF. However, we found higher remodeling processes after RF. Our data support previous publications showing different lesion formation in cryoablation and RF.

(PACE 2013; 36:31–36)
Proteomic changes associated with freeze‐thaw injury and post‐thaw recovery in onion (Allium cepa L.) scales
Authors: CHEN KETING , RENAUT JENNY , SERGEANT KJELL , WEI HUI , ARORA RAJEEV
Published: October 2012

The ability of plants to recover from freeze‐thaw injury is a critical component of freeze‐thaw stress tolerance. To investigate the molecular basis of freeze‐thaw recovery, here we compared the proteomes of onion scales from unfrozen control (UFC), freeze‐thaw injured (INJ), and post‐thaw recovered (REC) treatments. Injury‐related proteins (IRPs) and recovery‐related proteins (RRPs) were differentiated according to their accumulation patterns. Many IRPs decreased right after thaw without any significant re‐accumulation during post‐thaw recovery, while others were exclusively induced in INJ tissues. Most IRPs are antioxidants, stress proteins, molecular chaperones, those induced by physical injury or proteins involved in energy metabolism. Taken together, these observations suggest that while freeze‐thaw compromises the constitutive stress protection and energy supply in onion scales, it might also recruit ‘first‐responders’ (IRPs that were induced) to mitigate such injury. RRPs, on the other hand, are involved in the injury‐repair program during post‐thaw environment conducive for recovery. Some RRPs were restored in REC tissues after their first reduction right after thaw, while others exhibit higher abundance than their ‘constitutive’ levels. RRPs might facilitate new cellular homeostasis, potentially by re‐establishing ion homeostasis and proteostasis, cell‐wall remodelling, reactive oxygen species (ROS) scavenging, defence against possible post‐thaw infection, and regulating the energy budget to sustain these processes.
ArabidopsisROP‐interactive CRIB motif‐containing protein 1 (RIC1) positively regulates auxin signalling and negatively regulates abscisic acid (ABA) signalling during root development
Authors: CHOI YUNJUNG , LEE YUREE , KIM SOO YOUNG , LEE YOUNGSOOK , HWANG JAE‐UNG
Published: October 2012

Auxin and abscisic acid (ABA) modulate numerous aspects of plant development together, mostly in opposite directions, suggesting that extensive crosstalk occurs between the signalling pathways of the two hormones. However, little is known about the nature of this crosstalk. We demonstrate that ROP‐interactive CRIB motif‐containing protein 1 (RIC1) is involved in the interaction between auxin‐ and ABA‐regulated root growth and lateral root formation. RIC1 expression is highly induced by both hormones, and expressed in the roots of young seedlings. Whereas auxin‐responsive gene induction and the effect of auxin on root growth and lateral root formation were suppressed in theric1knockout, ABA‐responsive gene induction and the effect of ABA on seed germination, root growth and lateral root formation were potentiated. Thus, RIC1 positively regulates auxin responses, but negatively regulates ABA responses. Together, our results suggest that RIC1 is a component of the intricate signalling network that underlies auxin and ABA crosstalk.
Preferential Trade and Welfare with Differentiated Products
Authors: Konan Denise Eby , Maskus Keith E.
Published: October 2012

We consider analytically and numerically the welfare tradeoffs inherent in a preferential trade area (PTA) with products differentiated by region of origin. For a small open economy in such a setting, welfare gains are associated with higher trade volumes within the PTA. However, welfare losses are induced by declining tariff revenues on trade with non‐member countries. We show that both effects are concave, while one is a non‐monotonic and the other a potentially non‐monotonic function of pre‐PTA partner trade shares. Therefore, the relationship between initial partner import shares and direct static welfare impacts of a PTA are theoretically ambiguous. This finding contrasts with conventional results in the homogeneous‐goods case, whereby the smaller is the pre‐agreement trade volume with a potential partner the more beneficial is a PTA.
Trade Costs, Resource Reallocation and Productivity in Developing Countries
Authors: Blyde Juan , Iberti Gonzalo
Published: October 2012

New trade models with heterogeneous firms suggest that international trade plays an important role in reallocating resources from low to high productivity plants. We use plant‐level data from Chile and measures of trade costs that include tariffs and freight rates to analyze the importance of this trade‐induced market selection process. We find that trade costs affect the reallocation process through the various channels predicted by the theory; however, the effects are approximately half of those reported for the US. We also find that while the tariff rate is responsible for preventing some of the reallocation, transportation costs have the most limiting role in terms of the number of channels affected.
Does High‐skilled Migration Affect Publicly Financed Investments?
Authors: Grossmann Volker , Stadelmann David
Published: October 2012

This paper analyzes the interaction between migration of high‐skilled labor and publicly financed investment. We develop a theoretical model with multiple, ex ante identical jurisdictions where individuals decide on education and subsequent emigration. Migration decisions are based on differences in net income across jurisdictions which may occur endogenously. The interaction between income differences and migration flows gives rise to the potential of multiple equilibria: a symmetric equilibrium without migration and an asymmetric equilibrium in which net income levels differ among jurisdictions and trigger migration flows. In the former equilibrium, all jurisdictions have the same public investment level. In the latter one, public investment is high in host economies of skilled expatriates and low in source economies. We empirically test the hypothesis that emigration rates are negatively associated with publicly financed investment levels for OECD countries.
Selection, Market Size and International Integration: Do Vertical Linkages Play a Role?
Authors: Nocco Antonella
Published: October 2012

We analyze how increases in the market size and in the level of international integration affect the process of selection among firms with heterogeneous productivity levels when they are interconnected by vertical linkages. We show that when vertical linkages among firms are relatively weak (strong), an increase in the market size softens (toughens) the competition facing firms in this market and more firms of a lower (higher) efficiency survive, increasing (decreasing) the welfare level. Moreover, an increase in the level of economic integration softens competition only for intermediate vertical linkages, worsening the welfare level only for strong linkages.
Does Occupational Training by the Trade Adjustment Assistance Program Really Help Reemployment? Success Measured as Occupation Matching
Authors: Park Jooyoun
Published: October 2012

The Trade Adjustment Assistance Program provides various retraining opportunities to workers displaced due to import competition. This paper investigates whether successful skill acquisition through training—as opposed to general exposure to federal assistance—improves the post‐participation outcomes using the Trade Act Participant Report. Success in skill acquisition is indicated by a match between occupations of training and entered employment. The average matching rate for the sample is 37.53%. Trainees with a match display wage replacement rates that are 2 to 3 percentage points higher than those without one, while they display very similar post‐participation earnings that are inferior to that of non‐trainees. This generally indicates that participants with limited skill sets with lower pre‐participation earnings select into training, and successful skill acquisition offsets the negative impacts of their lack of marketable skills. Matching itself does not improve the retention at the job. However, participation in various training programs improves retention.
Foreign Banks and Credit Volatility: The Case of Latin American Countries
Authors: Haouat Meriem , Moccero Diego N. , Sosa Navarro Ramiro
Published: October 2012

The number of foreign banks in Latin America increased substantially over the period 1995–2001, prompting a debate on the potential consequences for host countries. Discussions focused on efficiency, the impact on competition and product market diversification in the banking industry, and the quality of the regulatory environment, among other issues. Against this background, this paper uses ARCH techniques to test the impact of foreign banks on both the level and the volatility of real private bank credit in a panel of eight Latin American countries, using quarterly data over the period 1995–2001. The empirical findings show that, together with financial development, the presence of foreign banks has contributed to reducing real credit volatility, improving the buffer shock function of the banking sector.
An Extended Ricardian Model Incorporating a Consumption Time Constraint
Authors: Tran‐Nam Binh
Published: October 2012

This paper investigates the impact of incorporating a Gossenian−Beckerian consumption time constraint into a simple Ricardian model. It is shown that in such a model the consumption gain from trade is zero, the specialization gain can be negative and a small nation devotes less labor to production after trade.
Trs130 Participates in Autophagy Through GTPases Ypt31/32 in Saccharomyces cerevisiae
Authors: Zou Shenshen , Chen Yong , Liu Yutao , Segev Nava , Yu Sidney , Liu Yan , Min Gaoyi , Ye Min , Zeng Yan , Zhu Xiaoping , Hong Bing , Björn Lars Olof , Liang Yongheng , Li Shaoshan , Xie Zhiping
Published: October 2012

Trs130 is a specific component of the transport protein particle II complex, which functions as a guanine nucleotide exchange factor (GEF) for Rab GTPases Ypt31/32. Ypt31/32 is known to be involved in autophagy, although the precise mechanism has not been thoroughly studied. In this study, we investigated the potential involvement of Trs130 in autophagy and found that both the cytoplasm‐to‐vacuole targeting (Cvt) pathway and starvation‐induced autophagy were defective in a trs130ts (trs130 temperature‐sensitive) mutant. Mutant cells could not transport Atg8 and Atg9 to the pre‐autophagosomal structure/phagophore assembly site (PAS) properly, resulting in multiple Atg8 dots and Atg9 dots dispersed in the cytoplasm. Some dots were trapped in the trans‐Golgi. Genetic studies showed that the effect of the Trs130 mutation was downstream of Atg5 and upstream of Atg1, Atg13, Atg9 and Atg14 on the autophagic pathway. Furthermore, overexpression of Ypt31 or Ypt32, but not of Ypt1, rescued autophagy defects in trs130ts and trs65ts (Trs130‐HA Trs120‐myc trs65Δ) mutants. Our data provide mechanistic insight into how Trs130 participates in autophagy and suggest that vesicular trafficking regulated by GTPases/GEFs is important in the transport of autophagy proteins from the trans‐Golgi to the PAS.
Risk factors for development of sterile haemorrhagic cystitis in canine lymphoma patients receiving oral cyclophosphamide: a case–control study
Authors: Gaeta R. , Brown D. , Cohen R. , Sorenmo K.
Published: October 2012

Sterile haemorrhagic cystitis (SHC) is a known risk of cyclophosphamide treatment; however, most canine reports are case series. This case–control study examined risk factors forSHCin dogs with lymphoma receiving oral cyclophosphamide. Twenty‐two dogs withSHCand 66 control dogs were identified. On univariate analysis,SHCrisk factors included age (P = 0.041), induction protocol (P = 0.021) and cumulative cyclophosphamide dose (P = 0.002). On multivariate analysis, increasing cumulative cyclophosphamide dose was associated with increased risk ofSHCand the ‘short’ induction protocol (protocol 1) was associated with decreased risk. Controlling for age and induction protocol, odds ofSHCincreased by 2.21 per 750 mg m−2increase in cyclophosphamide dose (P = 0.001).SHCfrom oral cyclophosphamide is a predominately delayed toxicity resulting from high cumulative doses.
Assuring Tube-to-Tubesheet Joint Tightness and Strength
Authors: Yokell Stanley
Published: October 2012

This paper describes preparing mockup tubesheet specimens for visual examination using a digital microscope to determine that tube-to-tubesheet joint welds are of the specified size and that expanded joints are satisfactory for the intended purpose. It discusses nondestructive examinations (NDE) of the tubesheets and tube joints intended to assure achieving sufficient tightness and strength to satisfy the uses to which the exchangers will be put. This paper refers to the ASME Boiler and Pressure Vessel Code (Code) paragraphs that apply to tube joint welds and expanded joints including shear load testing when the Code requires it [1]. The discussion also addresses the need for manufacturers to have qualified tube joining procedures and personnel qualified to use the qualified procedures. The work concludes with a summary of ways to assure tube joint tightness and strength.
Large Eddy Simulations of Film-Cooling Flows With a Micro-Ramp Vortex Generator
Authors: Shinn Aaron F. , Pratap Vanka S.
Published: October 2012

Large eddy simulations were performed to study the effect of a micro-ramp on an inclined turbulent jet interacting with a cross-flow in a film-cooling configuration. The micro-ramp vortex generator is placed downstream of the film-cooling jet. Changes in vortex structure and film-cooling effectiveness are evaluated. Coherent turbulent structures characteristic of a jet in a cross-flow are analyzed and the genesis of the counter-rotating vortex pair in the jet is discussed. Results are reported for two film-cooling configurations, where the primary difference is the way the jet inflow boundary conditions are prescribed. In the first configuration, the jet conditions are prescribed using a precursor simulation and in the second the jet is modeled using a plenum/pipe configuration. The latter configuration was designed based on previous wind tunnel experiments at NASA Glenn Research Center, and the present results are meant to supplement those experiments. It is found that the micro-ramp improves film-cooling effectiveness by generating near-wall counter-rotating vortices which help entrain coolant from the jet and transport it to the surface. The pair of vortices generated by the micro-ramp are of opposite sense to the vortex pair embedded in the jet.
Aerodynamic Performance of a Coolant Flow Off-Take Downstream of an Outlet Guide Vane
Authors: A’Barrow C. , Carrotte J. F. , Walker A. D. , Rolt A. M.
Published: October 2012

Within the compression system of a gas turbine engine a significant amount of air is removed to fulfill various requirements associated with cooling, ventilation, and sealing. Flow is usually removed through off-takes located in regions where space is restricted, while the flow is highly complex containing blade wakes, secondary flows, and other flow features. This paper investigates the performance of a pitot style off-take aimed at providing a high pressure recovery in a relatively short length. For this to be achieved some prediffusion of the flow is required upstream of the off-take (i.e., by making the off-take larger than the captured streamtube). Although applicable to a variety of applications, the system is targeted at an intercooled aero-engine concept where the off-take would be located aft of the fan outlet guide vane (OGV) root and provide coolant flow to the heat exchangers. Measurements and numerical predictions are initially presented for a baseline configuration with no off-take present. This enabled the OGV near field region to be characterized and provided a datum, relative to which the effects of introducing an off-take could be assessed. With the off-take present a variety of configurations were investigated including different levels of prediffusion, prior to the off-take, and different off-take positions. For very compact systems of short length, such that the gap between the OGV and off-take is relatively small, the amount of prediffusion achievable is limited by the off-take pressure field and its impact on the upstream OGV row. This pressure field is also influenced by parameters such as the nondimensional off-take height and splitter thickness. The paper analyses the relative importance of these various effects in order to provide some preliminary design rules. For systems of increased length a significant amount of flow prediffusion can be achieved with little performance penalty. However, the prediffusion level is eventually limited by the increased distortion and pressure losses associated with the captured streamtube.
Approach for Selection of Rayleigh Damping Parameters Used for Time History Analysis
Authors: Spears R. E. , Jensen S. R.
Published: October 2012

Nonlinearities, whether geometric or material, need to be addressed in seismic analysis. One good analysis method that can address these nonlinearities is direct time integration with Rayleigh damping. Modal damping is the damping typically specified in seismic analysis Codes and Standards (ASCE 4-98, 1998, “Seismic Analysis of Safety-Related Nuclear Structures and Commentary,” American Society of Civil Engineers, Reston, Virginia and ASCE/SEI 43-05, 2005, “Seismic Design Criteria for Structures, Systems, and Components in Nuclear Facilities,” American Society of Civil Engineers, Reston, Virginia.). Modal damping is constant for all frequencies where Rayleigh damping varies with frequency. An approach is proposed here for selection of Rayleigh damping coefficients to be used in seismic analyses that is consistent with given modal damping. The approach uses the difference between the modal damping response and the Rayleigh damping response along with effective mass properties of the model being evaluated to match overall system response levels. This paper provides a simple example problem to demonstrate the approach. It also provides results for a finite element model representing an existing piping system. Displacement, acceleration, and stress results are compared from model runs using modal damping and model runs using Rayleigh damping with coefficients selected using the proposed method.
Effects of Initial Crack Location on Failure Assessment Curves in Dissimilar Metal Weld Joints in Nuclear Power Plants
Authors: Gong N. , Wang G. Z. , Xuan F. Z. , Tu S. T.
Published: October 2012

Based on detailed three-dimensional finite element analyses, accurate, option 3, failure assessment curves (FACs) based on the R6 are constructed for a dissimilar metal weld joint (DMWJ) connecting the safe end to the pipe-nozzle of a reactor pressure vessel. The effects of initial crack location in the DMWJ structure on FACs are investigated. The results show that the plastic collapse of the DMWJ structure and the limit moment ML is mainly dominated by the plastic yield of the 316L material with lowest yield stress, and the crack locations in the DMWJ structure have less effect on the ML. When the load ratio Lr is less than 0.8, the crack locations have almost no effect on the FACs; while after the Lr is larger than 0.8, the crack locations have significant effect on the FACs. With the crack location moving from the safe end through the DMWJ toward the thickness transition in the pipe-nozzle, the FACs shift upward, which leads to a enlargement of the safe region in the failure assessment diagrams (FADs). This is mainly caused by the different properties of the materials in the DMWJ structure. To accurately assess the integrity of the DMWJ structure, the R6 option 3 FACs based on three-dimensional finite element analyses should be constructed and used for the cracks with different positions.
On the Use of Theory of Rings on Nonlinear Elastic Foundation to Study the Effect of Bolt Spacing in Bolted Flange Joints
Authors: Dan Do Tan , Bouzid Abdel-Hakim , Dao Thien-My
Published: October 2012

Bolted flange joints are extensively used to connect pressure vessels and piping equipment together. They are simple structures that offer the possibility of disassembly. However, they often experience leakage problems due to a loss of tightness as a result of a nonuniform distribution of gasket contact stresses in the radial and circumferential direction. Many factors contribute to such a failure; the flange and gasket stiffness and bolt spacing design combination being one of them. In our recent paper, the effects of bolt spacing were investigated based on the theory of circular beams resting on a linear elastic foundation (Do, T. D., Bouzid, A. H., and Dao, T.-M., 2011, “Effect of Bolt Spacing on the Circumferential Distribution of Gasket Contact Stress in Bolted Flange Joints,” ASME J. Pressure Vessel Technol., 133 (4), 041205). This paper is an extension of the work in which an analytical solution based on the real nonlinear gasket behavior is developed. This study focuses on the distribution of the gasket contact stress of two large diameter flanges, namely, a 52 in. and a 120 in. heat exchanger (HE) flanges. The nonlinear gasket behavior solution is compared to the Finite Element Analysis (FEA) and the linear gasket behavior solution for evaluation and comparison.
Prediction Method for Plastic Collapse of Circumferentially Cracked Pipes Subjected to Combined Bending and Torsion Moments
Authors: Li Yinsheng , Hasegawa Kunio , Hoang Phuong H. , Bezensek Bostjan
Published: October 2012

When a crack is detected in a pipe during in-service inspection, the failure estimation method given in the Codes such as the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section XI or the Japan Society of Mechanical Engineers (JSME) S NA-1-2008 can be applied to assess the integrity of the pipe. In the current edition of the ASME Code Section XI, the failure estimation method is provided for combined bending moment and pressure loads. The provision of evaluating torsion load is not made in the ASME Code Section XI. In this paper, finite element analyses are conducted for stainless steel pipes with a circumferential surface crack subjected to the combined bending and torsion moments, focusing on the entire range of torsion moments, including pure torsion. The effect of the internal pressure on failure behavior is also investigated. Based on the analysis results, a prediction method for plastic collapse under the combined loading conditions of bending and torsion is proposed for the general magnitude of torsion moments.
Type Synthesis of Underactuated Wrists Generated From Fully-Parallel Wrists
Authors: Di Gregorio Raffaele
Published: October 2012

Design criteria and constructive schemes are presented for a nonholonomic spherical (nS) pair proposed previously, along with a reconfigurable version of the same pair, named nS pair. Type synthesis of the underactuated parallel wrists derived from the fully parallel wrist (FPW) topology is addressed by replacing passive spherical (S) pairs with nS or nS pairs. Ten novel topologies of underactuated spherical wrists with practically the same workspace as the original FPW are identified. Wrist architectures based on these novel underactuated-wrist topologies are proved to be globally controllable, and a general path planning algorithm is proposed for these wrists. Here, the substitution of holonomic constraints with nonholonomic ones reduces the number of actuators and, sometimes, the number of links, too.
Optimization in Distributing Wind Generators on Different Places for Energy Demand Tracking
Authors: Elia Stefano , Gasulla Marc , De Francesco Antonio
Published: October 2012

Generation of distributed wind energy systems is being investigated as an answer to increased energy demand, since these systems achieve both economic and energy benefits. The purpose of the present article is to demonstrate a new method developed by the authors that optimizes the design of a wind production plant. Traditionally, the design strategy is primarily based on maximizing the economic benefit, to the detriment of other technical aspects. This study proposes a plant design method that, in a future with decreased governmental incentives, adapts the daily production curve to the demand curve with minimal decrease in economic benefit—a highly desirable result. This is achieved by installing generators in several locations that have different features of daily wind speed. In this way a better use of the energy is encouraged.
Fluid and Dynamics Analyses of a Gerotor Pump Using Various Span Angle Designs
Authors: Hsieh Chiu-Fan
Published: October 2012

This paper examines how the span angle design of its tooth profile affects the motion and pumping performance of a gerotor pump whose outer rotor profile is formed by an epicycloid and hypocycloid and whose inner rotor profile is obtainable by the theory of gearing. When the outer rotors have the same volume, the sealing performance of the rotor profile can be assessed using the curvature difference method, which indicates that sealing remains the same across various span angle designs. The tooth profile is built using mathematical models of the rotor, and fluid and dynamics analyses are conducted to predict actual pump operation. The overall fluid analysis, which models both compressibility and cavitation, clearly illustrates the complexity of the fluid flow inside the pump. Comparisons of the results for three separate span angle designs then reveal that the larger the span angle, the higher the area efficiency, outlet pressure, outlet flow rate, outlet flow velocity, and gas volume. A subsequent dynamics analysis further suggests that different span angle designs may lead to diverse contact force distribution on the inner and outer rotors. Hence, the research results provide useful guidelines for rotor design.
A Simplified Pseudo-Rigid-Body Model for Fixed-Fixed Flexible Segments
Authors: Lyon Scott M. , Howell Larry L.
Published: October 2012

The research presented in this paper focuses on the development of a simplified pseudo-rigid-body model for fixed-fixed flexible segments. The model predicts the path within ten percent of the results obtained from a chain algorithm for beam end angular deflections from negative fifty to fifty degrees and deflections up to sixty percent of the beam length. This error is larger than for pseudo-rigid-body models of other types of flexible segments but is still useful in preliminary design of compliant mechanisms. The model’s major advantage is that the force and moment are decoupled from the link length in the model, allowing the model to be used with traditional kinematic mechanism design and analysis techniques.
Design of Large-Displacement Compliant Joints
Authors: Moon Yong-Mo , Trease Brian Patrick , Kota Sridhar
Published: October 2012

Flexure joints are widely used to approximate the function of traditional mechanical joints, while offering the benefits of high precision, long life, and ease of manufacture. This paper investigates and catalogs the drawbacks of typical flexure connectors and presents several new designs for highly-effective, kinematically-behaved compliant joints. A revolute and a translational compliant joint are proposed (Figure 1), both of which offer great improvements over existing flexures in the qualities of (1) large range of motion, (2) minimal axis drift, (3) increased off-axis stiffness, and (4) reduced stress-concentrations. Analytic stiffness equations are developed for each joint and parametric computer models are used to verify their superior stiffness properties. A catalog of design charts based on the parametric models is also presented, allowing for rapid sizing of the joints for custom performance. Finally, two multi-degree-of-freedom joints are proposed as modifications to the revolute joint. These include a compliant universal joint and a compliant spherical joint, both designed to provide high degrees of compliance in the desired direction of motion and high stiffness in other directions.
Contact Aided Compliant Mechanisms: Concept and Preliminaries
Authors: Mankame Nilesh D. , Ananthasuresh G. K.
Published: October 2012

Compliant mechanisms (CMs) are the focus of active research because of the scalability, robustness and ease of manufacture endowed by their unitized construction. However, despite significant advances in development of systematic design techniques for these mechanisms, currently CMs are not capable of performing certain kinematic tasks that rigid body mechanisms can readily perform. This paper explores the use of contact interactions to enhance the functionality of CMs and thus widen their scope of application. Unlike CM designs without contact interactions, contact aided compliant mechanisms (CCMs) can be designed to generate non-smooth output port trajectories with a single continuous input. CCMs can also be designed to generate non-smooth force-deflection characteristics within the small deformation bounds imposed by linear elasticity. A wide variety of contact interactions, from the simple case involving a single point contact of a CM with a rigid external body to the more complex case of multiple contacts between different parts of the CM itself, can be used creatively to bridge the gap between the capabilities of CMs and conventional rigid body mechanisms. Several novel CCM designs that demonstrate useful non-smooth output trajectories are fabricated and tested. This paper also explores the use of optimization as a tool for systematic synthesis of CCMs. A simple one dimensional example is used to illustrate the use of topology optimization for systematic synthesis of a CCM for non-smooth force-deflection characteristics.
Dynamic Modeling of Multiple Cooperating Manipulators
Authors: Zhao Y. S. , Li Q. C. , Guan X. P. , Huang Z.
Published: October 2012

Based on influence coefficients theory of multi-closed-loop mechanism theory and virtual work principle, a novel methodology of dynamic modeling with corresponding computed torque control scheme for multiple cooperating robots is proposed. Load distribution principle of minimum squared sum of the joint torques is used. Only joint position and velocity variables are used in this control scheme. A numerical example has been provided to demonstrate the methodology as well as its feasibility.
Active Balancing of a Flexible Linkage With Redundant Drives
Authors: Yu Yue-Qing , Lin Jing
Published: October 2012

The dynamic balancing of flexible linkages that is a challenging topic in the dynamics of mechanisms is accomplished by active control with redundant drives for the first time in present study. The mathematical modal and dynamic equations of flexible mechanisms with redundant actuators are derived. The optimum shaking force and shaking moment balancing of a flexible linkage have been obtained through an active way of additional actuators. The effectiveness and advantage of redundant drives on the dynamic balancing of flexible mechanisms is fully demonstrated through an example of four-bar linkage.
An Efficient Solution of the Elastic Mechanism Non-Linear Differential Equation of Motion
Authors: Wang Jianping , Lu Hongzhao , Yuan Daning
Published: October 2012

A general form of non-linear differential motion equations for the elastic mechanism is presented. Based on the analysis of the structure property of the equations, a numerical solution method which combines the State Space Method with Iterative Method is put forward. The solution efficiency and precision are improved greatly through analyzing the solution method of the matrix exponent function and the equations with belt shape and side block coefficient matrices. Finally, as an example, the dynamic properties of a mold oscillation mechanism with 4-eccentric axes for continuous casting machine are analyzed. The results illustrate the correctness and feasibility of the method.
The Interaction Between Contact Loads and Tooth Wears of Engaged Plastic Gear Pairs
Authors: Kuang Jao-Hwa , Lin Ah-Der
Published: October 2012

The interaction between the dynamic contact loads and the tooth profile wears of a meshing plastic gear pair is simulated and investigated in this study. A dynamic model of a plastic gear pair is presented. The effects of position-varying mesh stiffness, damping ratio, load sharing, tooth profile errors and temperature variation, on the dynamic contact loads are included in this model. The tooth wear equation proposed by Flodin et al is used to simulate the tooth wear and the tooth profile variation. The variation of the contact load introduced from the cumulative tooth profile wear is simulated and analyzed. Numerical results indicate that the dynamic load histogram of an engaging plastic gear pair may change greatly with the tooth wear.
An Object-Oriented Graphical Interface for Dynamic Finite Element Modeling of Belt-Drives
Authors: Wasfy Tamer M. , Leamy Michael
Published: October 2012

An object-oriented graphical interface, which includes integrated pre-processor, post-processor, and finite element solver, for predicting the dynamic response of belt-drives is described. Three classes of objects are used in the model: geometric objects, support objects, and finite elements. The user can graphically construct a belt-drive by inserting the geometric objects and changing their properties. The user can also add support objects such as physical materials and time-histories of known quantities. The pre-processor automatically generates the finite element model of the belt-drive and submits it to the solver for analysis. The post-processor is used to display the analysis results, which include an animation of the motion of the belt-drive and various types of graphs of response quantities (such as time-history, frequency, snapshot and time-averaged graphs). The graphical output of the pre-processor and the post-processor can be displayed either on the computer screen or in an immersive stereoscopic virtual-reality facility.
Gear Walk Instability Studies Using a Vibration Model of a Reduced Scale Landing Gear System
Authors: Balasubramanian Karthik , Farhang Kambiz
Published: October 2012

Gear walk is a dynamic instability condition that can pose serious harm to an aircraft and its passengers. The instability is believed to be borne as a result of braking, in which vibration of the landing gear can be induced generating motion reminiscent of a walking movement. This paper focuses on the theoretical account of a Reduced Scale Landing Gear (RSLG) apparatus and studies gear walk phenomenon. The mathematical approach involves lumped-parameter model representation of the RSLG that accounts for the landing gear’s struts, the wheels and the caliper-disc brake dynamics. The theoretical treatment of the RSLG apparatus entails consideration of the structure of the device that includes the account of dynamic response of the assembly consisting of a fuselage, two struts and two wheels. Various physical and geometrical parameters are determined and included in the mathematical model of the apparatus. It is demonstrated that the occurrence of gear walk vibration is greatly influenced by the structural stiffness of the system. Both synchronous and 180° out of phase motion of the struts are generated in a parametric study in which structural stiffness is varied.
Two Basic Features of Instantaneous Conjugate Motion and Their Importance in Facilitating Motion Analysis
Authors: Chen Chih-Hsin , Chen Janet Hong-Jian
Published: October 2012

Two basic features of instantaneous conjugate motion, which distinguishes it from instantaneous free body motion, are pointed out. Their influences on the geometrical constraints requisite for surface/line conjugation are discussed. Their importance in facilitating motion analysis of mechanical systems through linearization of relevant equations is clarified. Two illustrative examples are cited.
Jacobian Analysis of Limited-DOF Parallel Manipulators
Authors: Joshi Sameer A. , Tsai Lung-Wen
Published: October 2012

This paper presents a methodology for the Jacobian analysis of limited degrees-of-freedom (DOF) parallel manipulators. A limited-DOF parallel manipulator is a spatial parallel manipulator which has less than six degrees-of-freedom. It is shown that a 6 × 6 Jacobian matrix, which provides complete information about singularities, can be derived by making use of the theory of reciprocal screws. The 3-UPU and 3-RPS parallel manipulators are used as examples to demonstrate the methodology.
Synthesis and Analysis of a Group of 3-Degree-of-Freedom Decoupling Parallel Manipulators
Authors: Jin Qiong , Yang Ting-Li
Published: October 2012

Based on topological structure characteristics of the parallel mechanisms, the internal relationship between kinematics decoupling and mobility types of mechanisms is revealed, and the basic principle for structural synthesis of topological decoupling mechanisms is put forward. Using this theory, a group of 3 degree-of-freedom (DOF) partial decoupling manipulators could be synthesized, the expected kinematic outputs of which are 1-DOF translation and 2-DOF rotation, and the unexpected outputs of which are constants. The kinematic analysis demonstrates that these manipulators can be easily controlled in real time and their paths planning can be also reached due to the partial decoupling property for kinematics.