Adsorption and desorption of sulfur dioxide on novel adsorbents for flue gas desulfurization. Final report, September 1, 1993--August 31, 1994

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Y.S.

Dry regenerative sorption processes have recently attracted increasing attention in flue gas desulfurization (FGD) because of their several advantages over the conventional wet-scrubbing processes. Dry sorbents are usually made by coating a transition or alkaline earth metal precursor on the surface of a porous support. Major disadvantages of these sorbents prepared by the conventional methods include relatively poor attrition resistance and low SO{sub 2} sorption capacity. The physical and especially chemical attrition (associated with the sulphation-oxidation-reduction cycles in the process) deteriorates the performance of the sorbents. The low SO{sub 2} sorption capacity is primarily due to the small surface areamore » of the support. Materials with a high surface area are not used as the supports for FGD sorbents because these materials usually are not thermally stable at high temperatures. In the past year, the research supported by Ohio Coal Development Office was focused on synthesis and properties of sol-gel derived alumina and zeolite sorbents with improved properties for FGD. The sol-gel derived alumina has large surface area, mesopore size and excellent mechanical strength. Some alumina-free zeolites not only posses the basic properties required as a sorbent for FGD (hydrophobicity, thermal and chemical stability, mechanical strength) but also have extremely large surface area and selective surface chemistry. The major objectives of this research program were to synthesize the sol-gel derived sorbents and to explore the use of the zeolites either directly as adsorbents or as sorbent support for FGD. The research was aimed at developing novel FGD sorbents possessing better sorption equilibrium and kinetic properties and improved physical and chemical attrition resistance.« less

Controlling Surface Chemistry to Deconvolute Corrosion Benefits Derived from SMAT Processing

NASA Astrophysics Data System (ADS)

Murdoch, Heather A.; Labukas, Joseph P.; Roberts, Anthony J.; Darling, Kristopher A.

2017-07-01

Grain refinement through surface plastic deformation processes such as surface mechanical attrition treatment has shown measureable benefits for mechanical properties, but the impact on corrosion behavior has been inconsistent. Many factors obfuscate the particular corrosion mechanisms at work, including grain size, but also texture, processing contamination, and surface roughness. Many studies attempting to link corrosion and grain size have not been able to decouple these effects. Here we introduce a preprocessing step to mitigate the surface contamination effects that have been a concern in previous corrosion studies on plastically deformed surfaces; this allows comparison of corrosion behavior across grain sizes while controlling for texture and surface roughness. Potentiodynamic polarization in aqueous NaCl solution suggests that different corrosion mechanisms are responsible for samples prepared with the preprocessing step.

Experimental study of microstructure changes due to low cycle fatigue of a steel nanocrystallised by Surface Mechanical Attrition Treatment (SMAT)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Z.

Electron Backscatter Diffraction technique is used to characterize the microstructure of 316L steel generated by Surface Mechanical Attrition Treatment (SMAT) before and after low cycle fatigue tests. A grain size gradient is generated from the top surface to the interior of the samples after SMAT so that three main regions can be distinguished below the treated surface: (i) the ultra-fine grain area within 5 μm under the top surface with preferably oriented grains, (ii) the intermediate area where the original grains are partially transformed, and (iii) the edge periphery area where the original grains are just mechanically deformed with themore » presence of plastic slips. Fatigue tests show that cyclic loading does not change the grain orientation spread and does not activate any plastic slip in the ultra-fine grain top surface area induced by SMAT. On the opposite, in the plastically SMAT affected region including the intermediate area and the edge periphery area, new slip systems are activated by low cycle fatigue while the grain orientation spread is increased. These results represent a first very interesting step towards the characterization and understanding of mechanical mechanisms involved during the fatigue of a grain size gradient material. - Highlights: •LCF tests are carried out on specimens processed by SMAT. •EBSD is used to investigate microstructural changes induced by LCF. •A grain size gradient is generated by SMAT from surface to the bulk of the fatigue samples. •New slip systems are activated by LCF and GOS is increased in plastically deformed region. •However, these phenomena are not observed in the top surface ultra-fine grain area.« less

Nanocrystalline-grained tungsten prepared by surface mechanical attrition treatment: Microstructure and mechanical properties

NASA Astrophysics Data System (ADS)

Guo, Hong-Yan; Xia, Min; Wu, Zheng-Tao; Chan, Lap-Chung; Dai, Yong; Wang, Kun; Yan, Qing-Zhi; He, Man-Chao; Ge, Chang-Chun; Lu, Jian

2016-11-01

A nanostructured surface layer was fabricated on commercial pure tungsten using the method of surface mechanical attrition treatment (SMAT). The microstructure evolution of the surface layer was characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and its formation mechanism was discussed as well. Both refinement and elongation of the brittle W grains were confirmed. The elongated SMATed W was heavily strained, the maximum value of the strain at the grain boundaries reaches as high as 3-5%. Dislocation density in the SMATed W nanograins was found to be 5 × 1012 cm-2. The formation of the nanograins in the top surface layer of the W was ascribed to the extremely high strain and strain rate, as well as the multidirectional repetitive loading. Bending strength of commercial W could be improved from 825 MPa to 1850 MPa by SMAT process. Microhardness results indicated the strain range in SMATed W can reach up to 220 μm beneath the top surface. The notched Charpy testing results demonstrated that SMATed W possess higher ductility than that of commercial W. The top surface of the W plates with and without SMATe processing possesses residual compressive stress of about -881 MPa and -234 MPa in y direction, and -872 MPa and -879 MPa in x direction respectively. The improvement of toughness (DBTT shift) of SMATed W may be the synergistic effect of residual compressive stress, dislocation density improvement and microstructure refinement induced by SMAT processing. SMAT processing could be a complementary method to further decrease the DBTT value of tungsten based materials.

Erosion and attrition of human enamel in vitro part I: interaction effects.

PubMed

Eisenburger, M; Addy, M

2002-01-01

The aim of the study in vitro was to measure the interplay of attrition and erosion of human enamel under several different pH conditions. Cusp and smooth surface enamel specimens were prepared from unerupted human third molar teeth. Cusp and smooth surface specimens opposed each other in a wear machine under a load of 600 g. The machine simulated tooth grinding for 30 min (2280 wear cycles). Six groups of 10 specimens were worn in the following environmental conditions: saline, citric acid at pH values of 3.2, 5.5 or 7.0 and two cycling groups (pH 3.2/saline or saline/pH 3.2). Additionally, 10 smooth surface specimens were exposed to the same fluids without attrition. Tissue loss on smooth surface specimens was determined by profilometry. The worn specimen surfaces were studied by SEM. Attrition depth in saline and pH 7.0 citric acid was 25.5 microm. At pH 3.2 and 5.5 attrition depths were 6.0 and 4.3 microm, respectively. Cycling in saline/citric acid and vice versa produced attrition depths of 9.2 and 7.9 microm, respectively. In the erosion only specimens lesion depths were 3.0, 1.2 and 0 microm at pH 3.2, 5.5 and 7.0 and saline, respectively. Attrition specimens at pH 7.0 and in saline showed very rough surfaces. At low pH enamel surfaces appeared flat and smooth. Enamel wear in neutral conditions is significantly higher than in acidic conditions (p < 0.05), apparently due to a smoothing effect of erosion on contacting surfaces. Copyright 2002 Elsevier Science Ltd.

Prevention of weld-decay in austenitic stainless steel by using surface mechanical attrition treatment

NASA Astrophysics Data System (ADS)

Laleh, Majid; Kargar, Farzad; Rouhaghdam, Alireza Sabour

2012-11-01

Surface mechanical attrition treatment (SMAT) was applied to the samples of a type AISI 304 stainless steel in order to induce grain refinement as well as formation of twins. Transmission electron microscopy and X-ray diffraction analysis results showed that the average grain size at the surface of the SMATed sample was about 10 nm. The untreated and SMATed samples were then welded using a one-pass gas tungsten arc procedure. The heat-affected zone (HAZ) of the samples was examined by optical microscopy and corrosion tests. Results of the double loop electrochemical potentiokinetic reactivation tests showed that the degree of sensitization in the HAZ for the SMATed sample was very low as compared to that of the untreated one. The pre-SMATed sample was resistant to intergranular corrosion. This is mainly due to the formation of high density of twins which are not prone to carbide precipitation because of their regular and coherent atomic structure and extreme low grain boundary energy as compared with those of other grain boundaries.

Influence of attrition milling on nano-grain boundaries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rawers, J.; Cook, D.

1999-03-01

Nanostructured materials have a relatively large proportion of their atoms associated with the grain boundary, and the method used to develop the nano-grains has a strong influence on the resulting grain boundary structure. In this study, attrition milling iron powders and blends of iron powders produced micron-size particles composed of nano-size grains. Mechanical cold-working powder resulted in dislocation generation, multiplication, and congealing that produced grain refinement. As the grain size approached nano-dimensions, dislocations were no longer sustained within the grain and once generated, rapidly diffused to the grain boundary. Dislocations on the grain boundary strained the local lattice structure which,more » as the grain size decreased, became the entire grain. Mechanical alloying of substitutional aluminium atoms into iron powder resulted in the aluminium atoms substituting for iron atoms in the grain boundary cells and providing a grain boundary structure similar to that of the iron powder processed in argon. Attrition milling iron powder in nitrogen gas resulted in nitrogen atoms being adsorbed onto the particle surface. Continued mechanical milling infused the nitrogen atoms into interstitial lattice sites on the grain boundary which also contributed to expanding and straining the local lattice.« less

In-depth quantitative analysis of the microstructures produced by Surface Mechanical Attrition Treatment (SMAT)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samih, Y., E-mail: youssef.samih@univ-lorraine.fr; Université de Lorraine, Laboratory of Excellence on Design of Alloy Metals for low-mAss Structures; Beausir, B.

2013-09-15

Electron BackScattered Diffraction (EBSD) maps are used to characterize quantitatively the graded microstructure formed by Surface Mechanical Attrition Treatment (SMAT) and applied here to the 316L stainless steel. In particular, the analysis of GNDs – coupled with relevant and reliable criteria – was used to depict the thickness of each zone identified in the SMAT-affected layers: (i) the “ultrafine grain” (UFG) zone present at the extreme top surface, (ii), the “transition zone” where grains were fragmented under the heavy plastic deformation and, finally, (iii) the “deformed zone” where initial grains are simply deformed. The interest of this procedure is illustratedmore » through the comparative analysis of the effect of some SMAT processing parameters (amplitude of vibration and treatment duration). The UFG and transition zones are more significantly modified than the overall affected thickness under our tested conditions. - Highlights: • EBSD maps are used to characterize quantitatively the microstructure of SMAT treated samples. • Calculation of the GND density to quantify strain gradients • A new method to depict the different zone thicknesses in the SMAT affected layer • Effects of SMAT processing parameters on the surface microstructure evolution.« less

On the effectiveness of surface severe plastic deformation by shot peening at cryogenic temperature

NASA Astrophysics Data System (ADS)

Novelli, M.; Fundenberger, J.-J.; Bocher, P.; Grosdidier, T.

2016-12-01

The effect of cryogenic temperature (CT) on the graded microstructures obtained by severe shot peening using surface mechanical attrition treatment (SMAT) was investigated for two austenitic steels that used different mechanisms for assisting plastic deformation. For the metastable 304L steel, the depth of the hardened region increases because CT promotes the formation of strain induced martensite. Comparatively, for the 310S steel that remained austenitic, the size of the subsurface affected region decreases because of the improved strength of the material at CT but the fine twinned nanostructures results in significant top surface hardening.

Carbon attrition during the circulating fluidized bed combustion of a packaging-derived fuel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mastellone, M.L.; Arena, U.

1999-05-01

Cylindrical pellets of a market-available packaging-derived fuel, obtained from a mono-material collection of polyethylene terephthalate (PET) bottles, were batchwise fed to a laboratory scale circulating fluidized bed (CFB) combustor. The apparatus, whose riser was 41 mm ID and 4 m high, was operated under both inert and oxidizing conditions to establish the relative importance of purely mechanical attrition and combustion-assisted attrition in generating carbon fines. Silica sand particles of two size distributions were used as inert materials. For each run, carbon load and carbon particle size distribution in the riser and rates of attrited carbon fines escaping the combustor weremore » determined as a function of time. A parallel investigation was carried out with a bubbling fluidized bed (BFB) combustor to point out peculiarities of attrition in CFB combustors. After devolatilization, PET pellets generated fragile aggregates of char and sand, which easily crumbled, leading to single particles, partially covered by a carbon-rich layer. The injected fixed carbon was therefore present in the bed in three phases: an A-phase, made of aggregates of sand and char, an S-phase, made of individual carbon-covered sand particles and an F-phase, made of carbon fines, abraded by the surfaces of the A- and S-phases. The effects of the size of inert material on the different forms under which fixed carbon was present in the bed and on the rate of escape of attrited carbon fines from the combustor were investigated. Features of carbon attrition in CFB and BFB combustors are discussed.« less

The Bulk Nanocrystalline zn Produced by Mechanical Attrition

NASA Astrophysics Data System (ADS)

Zhu, X. K.; Zhao, K. Y.; Li, C. J.; Tao, J. M.; Chan, T. L.; Koch, C. C.

The purpose of experiment was to produce bulk nanocrystalline Zn by mechanical attrition. The bulk nanocrystalline Zn produced by mechanical attrition was studied. The microstructural evolution during cryomilling and subsequent room temperature milling was characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). In this paper, Nanocrystalline Zn was produced by insitu consolidation of Zn elemental powder using mechanical attrition at liquid nitrogen and room temperature. For the samples studied, the longest elongation of 65% and highest stress of 200 MPa is obtained in nanocrystalline Zn during tensile testing at the condition of strain rate (10-3 sec-1) and 20°C which is equal to 0.43 Tm (Tm is the melting temperature of pure Zn).

Blue-Collar Scholars?: Mediators and Moderators of University Attrition in First-Generation College Students

ERIC Educational Resources Information Center

Martinez, Julia A.; Sher, Kenneth J.; Krull, Jennifer L.; Wood, Phillip K.

2009-01-01

Many college entrants' parents do not have college degrees. These entrants are at high risk for attrition, suggesting it is critical to understand mechanisms of attrition relative to parental education. Moderators and mediators of the effect of parental education on attrition were investigated in 3,290 students over 4 years. Low parental education…

Blue-Collar Scholars?: Mediators and Moderators of University Attrition in First-Generation College Students

PubMed Central

Martinez, Julia A.; Sher, Kenneth J.; Krull, Jennifer L.; Wood, Phillip K.

2009-01-01

Many college entrants’ parents do not have college degrees. These entrants are at high risk for attrition, suggesting it is critical to understand mechanisms of attrition relative to parental education. Moderators and mediators of the effect of parental education on attrition were investigated in 3,290 students over 4 years. Low parental education was a risk for attrition; importantly, college GPAs both moderated and mediated this effect, and ACT scores, scholarships, loans, and full-time work mediated this effect. Drug use, psychological distress, and few reported academic challenges predicted attrition, independent of parental education. These findings might inform interventions to decrease attrition. PMID:19750141

3D Simulation Modeling of the Tooth Wear Process.

PubMed

Dai, Ning; Hu, Jian; Liu, Hao

2015-01-01

Severe tooth wear is the most common non-caries dental disease, and it can seriously affect oral health. Studying the tooth wear process is time-consuming and difficult, and technological tools are frequently lacking. This paper presents a novel method of digital simulation modeling that represents a new way to study tooth wear. First, a feature extraction algorithm is used to obtain anatomical feature points of the tooth without attrition. Second, after the alignment of non-attrition areas, the initial homogeneous surface is generated by means of the RBF (Radial Basic Function) implicit surface and then deformed to the final homogeneous by the contraction and bounding algorithm. Finally, the method of bilinear interpolation based on Laplacian coordinates between tooth with attrition and without attrition is used to inversely reconstruct the sequence of changes of the 3D tooth morphology during gradual tooth wear process. This method can also be used to generate a process simulation of nonlinear tooth wear by means of fitting an attrition curve to the statistical data of attrition index in a certain region. The effectiveness and efficiency of the attrition simulation algorithm are verified through experimental simulation.

3D Simulation Modeling of the Tooth Wear Process

PubMed Central

Dai, Ning; Hu, Jian; Liu, Hao

2015-01-01

Severe tooth wear is the most common non-caries dental disease, and it can seriously affect oral health. Studying the tooth wear process is time-consuming and difficult, and technological tools are frequently lacking. This paper presents a novel method of digital simulation modeling that represents a new way to study tooth wear. First, a feature extraction algorithm is used to obtain anatomical feature points of the tooth without attrition. Second, after the alignment of non-attrition areas, the initial homogeneous surface is generated by means of the RBF (Radial Basic Function) implicit surface and then deformed to the final homogeneous by the contraction and bounding algorithm. Finally, the method of bilinear interpolation based on Laplacian coordinates between tooth with attrition and without attrition is used to inversely reconstruct the sequence of changes of the 3D tooth morphology during gradual tooth wear process. This method can also be used to generate a process simulation of nonlinear tooth wear by means of fitting an attrition curve to the statistical data of attrition index in a certain region. The effectiveness and efficiency of the attrition simulation algorithm are verified through experimental simulation. PMID:26241942

Characterization of transparent dentin in attrited teeth using optical coherence tomography.

PubMed

Mandurah, Mona M; Sadr, Alireza; Bakhsh, Turki A; Shimada, Yasushi; Sumi, Yasunori; Tagami, Junji

2015-05-01

Attrition and wear of tooth surface occur with aging and result in loss of enamel, with exposure and histological changes in dentin. Dealing with attrited teeth and restoration of the lost tissue are clinically challenging. The main objective of this study is to characterize the exposed transparent dentin in the occlusal surface of attrited teeth by optical coherence tomography (OCT). Naturally attrited, extracted human teeth with occlusal-transparent dentin were investigated in comparison to sound and carious teeth. The teeth were subjected to OCT imaging and then cross-sectioned and polished. OCT B-scans were compared to light microscopy images of the same cross section. In OCT images, some changes were evident at the transparent dentin in attrited teeth. An OCT attenuation coefficient parameter (μ t) was derived based on the Beer-Lambert law as a function of backscatter signal slope. The mean values of μ t were 1.05 ± 0.3, 2.23 ± 0.4, and 0.61 ± 0.27 mm(-1) for sound, carious, and transparent dentins, respectively. One-way ANOVA with Tukey's post-hoc showed a significant difference between groups (p < 0.05). Physiological changes in transparent dentin that involve deposition of mineral casts in the dentinal tubules lead to lower attenuation of OCT signal. OCT has a potential role to detect transparent dentin on the surface of attrited teeth and can be used in the future as a clinical adjunct tool.

Attrition, abrasion, corrosion and abfraction revisited: a new perspective on tooth surface lesions.

PubMed

Grippo, John O; Simring, Marvin; Schreiner, Steven

2004-08-01

The authors propose updated and revised nomenclature, definitions and classification for tooth surface lesions. Their objective is standardization, clarity and clinical utility for the dental practitioner. The article presents a schema of the pathodynamic mechanisms in the formation of tooth surface lesions--three basic physical and chemical mechanisms, their interactions and their dental manifestations. The use of precise definitions will assist the practitioner in determining the etiology of various tooth surface lesions. Understanding the pathodynamic mechanisms and their many possible interactions, as set forth in the schema, will enable the practitioner to make an accurate differential diagnosis and to provide effective prevention and treatment. It also will assist dentists in communicating more effectively with their colleagues as well as with their patients. In addition, the schema helps identify areas in which future research is indicated.

Enhanced nitrogen diffusion induced by atomic attrition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ochoa, E.A.; Figueroa, C.A.; Czerwiec, T.

2006-06-19

The nitrogen diffusion in steel is enhanced by previous atomic attrition with low energy xenon ions. The noble gas bombardment generates nanoscale texture surfaces and stress in the material. The atomic attrition increases nitrogen diffusion at lower temperatures than the ones normally used in standard processes. The stress causes binding energy shifts of the Xe 3d{sub 5/2} electron core level. The heavy ion bombardment control of the texture and stress of the material surfaces may be applied to several plasma processes where diffusing species are involved.

The effects of three different food acids on the attrition-corrosion wear of human dental enamel

NASA Astrophysics Data System (ADS)

Zhang, Yichi; Arsecularatne, Joseph A.; Hoffman, Mark

2015-07-01

With increased consumption of acidic drinks and foods, the wear of human teeth due to attrition in acidic environments is an increasingly important issue. Accordingly, the present paper investigates in vitro the wear of human enamel in three different acidic environments. Reciprocating wear tests in which an enamel cusp slides on an enamel flat surface were carried out using acetic, citric and lactic acid lubricants (at pH 3-3.5). Distilled water was also included as a lubricant for comparison. Focused ion beam milling and scanning electron microscopy imaging were then used to investigate the enamel subsurfaces following wear tests. Nanoindentation was used to ascertain the changes in enamel mechanical properties. The study reveals crack generation along the rod boundaries due to the exposure of enamel to the acidic environments. The wear mechanism changes from brittle fracture in distilled water to ploughing or shaving of the softened layer in acidic environments, generating a smooth surface with the progression of wear. Moreover, nanoindentation results of enamel samples which were exposed to the above acids up to a duration of the wear tests show decreasing hardness and Young’s modulus with exposure time.

[Clinical observation of using composite resin to fill dental attrition on occlusal surface].

PubMed

Guo, Li-juan; Xu, Yan; Chen, Guang-quan

2005-10-01

The purpose of this study was to evaluate the clinical effect of using composite resin to fill dental attrition on occlusal surface. Whether the dental attrition had enough space to the material was determined first. Sometimes grinding the sharp and steep cusps or ridges of the opposite teeth was needed. Then the dental attrition was cleaned thoroughly, and finally filled with CLEARFIL bond and composite resin without preparing cavity. The follow-up period was 1 year. Out of 70 teeth from 25 patients, 52 were successful, 16 were curative, and 2 were failed. The curative rate was 97.14%. The method avoids endangering the dental pulp. It was easily accepted by the patients and operated by dentists, and can be widely applied in clinical cases.

Influence of SMAT Parameters on Microstructural and Mechanical Properties of Al-Mg-Si Alloy AA 6061

NASA Astrophysics Data System (ADS)

Anand Kumar, S.; Satish Kumar, P.; Ganesh Sundara Raman, S.; Sankara Narayanan, T. S. N.

2017-04-01

In the present work, the influence of surface mechanical attrition treatment (SMAT) parameters on the microstructural and mechanical properties of an aluminum-magnesium-silicon alloy AA 6061 was studied using design of experiment technique. Balls of three different diameters were used, and SMAT was done for three different durations. The microstructural features of the surface layer fabricated by SMAT were characterized by cross-sectional scanning electron microscopic observations, x-ray diffraction technique and transmission electron microscopy. The microindentation hardness, nanoindentation hardness and surface roughness were determined. Due to SMAT, nanocrystallites formed on the surface and near-surface regions, and hardness and surface roughness increased. The ball diameter was the most influencing SMAT parameter compared to the treatment duration. However, interaction between ball diameter and treatment duration could not be ignored. Regression equations were developed relating the process parameters to the surface properties. The ball diameter and treatment duration could thus be properly selected as per the required values of roughness and/or the hardness.

Attrition reactor system

DOEpatents

Scott, Charles D.; Davison, Brian H.

1993-01-01

A reactor vessel for reacting a solid particulate with a liquid reactant has a centrifugal pump in circulatory flow communication with the reactor vessel for providing particulate attrition, resulting in additional fresh surface where the reaction can occur.

Attrition of precipitated iron Fischer-Tropsch catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Datye, A.K.; Reardon, J.; Hanprasopwattana, A.

1996-12-31

Precipitated Iron catalysts used in slurry phase bubble column reactors are known to undergo attrition during use. The attrition reduces the lifetime of the catalyst as well as causing problems in separating the product liquids from the catalyst. In this study, the authors have investigated the underlying mechanisms that lead to attrition in precipitated iron catalysts. They have discovered that attrition takes place on two length scales. On the macro scale, attrition is caused by the break-up of the weak agglomerates that constitute this catalyst into individual crystallites. Addition of binders such as kaolin does not help significantly in strengtheningmore » the catalyst particles. In addition, there is a second process leading to nanoscale attrition that is caused by the break-up of individual iron oxide crystallites into nano particles of iron carbide as the catalyst is activated for reaction. Design of attrition resistant F-T catalysts must consider these two modes of catalyst attrition. Preliminary work in the laboratory directed at improving the attrition resistance of precipitated iron catalysts will also be described in this paper.« less

The effect of increasing sodium fluoride concentrations on erosion and attrition of enamel and dentine in vitro.

PubMed

Austin, R S; Rodriguez, J M; Dunne, S; Moazzez, R; Bartlett, D W

2010-10-01

To investigate the effect of an aqueous sodium fluoride solution of increasing concentration on erosion and attrition of enamel and dentine in vitro. Enamel and dentine sections from caries-free human third molars were polished flat and taped (exposing a 3 mm x 3 mm area) before being randomly allocated to 1 of 5 groups per substrate (n=10/gp): G1 (distilled water control); G2 (225 ppm NaF); G3 (1450 ppm NaF); G4 (5000 ppm NaF); G5 (19,000 ppm NaF). All specimens were subjected to 5, 10 and 15 cycles of experimental wear [1 cycle=artificial saliva (2h, pH 7.0)+erosion (0.3% citric acid, pH 3.2, 5 min)+fluoride/control (5 min)+attrition (60 linear strokes in artificial saliva from enamel antagonists loaded to 300 g)]. Following tape removal, step height (SH) in mum was measured using optical profilometry. When the number of cycles increased the amount of tooth surface loss increased significantly in enamel and dentine after attrition and erosion and for dentine after attrition. Attrition and erosion resulted in greater surface loss than attrition alone after 15 cycles of experimental wear of enamel. 5000 ppm and 19,000 ppm sodium fluoride solutions had a protective effect on erosive and attritional enamel tooth wear in vitro, however no other groups showed significant differences. The more intensive the fluoride regime the more protection was afforded to enamel from attrition and erosion. However, in this study no such protective effect was demonstrated for dentine. Copyright 2010 Elsevier Ltd. All rights reserved.

Attrition reactor system

DOEpatents

Scott, C.D.; Davison, B.H.

1993-09-28

A reactor vessel for reacting a solid particulate with a liquid reactant has a centrifugal pump in circulatory flow communication with the reactor vessel for providing particulate attrition, resulting in additional fresh surface where the reaction can occur. 2 figures.

Development of Surface Mechanical Attrition Treatment (SMAT) and Electrodeposition Process for Generating Nanostructured Materials and Study of Their Tensile Properties

NASA Astrophysics Data System (ADS)

Chan, Hoi Lam

This work systematically investigates two of the most promising synthesis methods for producing nanostructured (NS) materials: surface mechanical attrition treatment (SMAT) and the electrodeposition (ED) process, and obtains the proper conditions for fabricating NS materials in bulk form and studies the properties of these materials. SMAT is one of the recently developed processes to form nano-crystallized surface layer and refine grains in the subsurface layers, by actuating a number of spherical projectiles to impact the sample surface. In this work, the detailed measurement of ball impinging velocity is presented, and the resulted strain-rate and strains are theoretically modeled. Consequently the relation between plastic strain history and the observed microstructures is established. The SMAT process with different numbers of balls is explored to manifest that an optimum number of balls exists for the highest efficiency. ED process is widely used in producing NS materials these days. In this work, the relationships among non-metallic substrates, current type, current densities, microstructure and crystallographic textures, and mechanical properties is presented in order to demonstrate the influences of the deposition parameters in obtaining nano-grains and nano-twins microstructures. This work also examines the availability of obtaining bulk NS materials with desirable ductility in production-scale conditions through understanding these relationships. In the last part of the study, the effect of SMAT on the electrodeposits is studied. Tensile properties, microstructures and textures of the SMATed electrodeposits have been examined. The results demonstrate that the NS matrix obtained by the ED process with sufficient thickness retains desirable ductility after employing SMAT technology, and the SMAT process further enhances the strength of the electrodeposits.

Attrition of coal ash particles in a fluidized-bed reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tomeczek, J.; Mocek, P.

2007-05-15

Experimental data of ash-particles attrition in a fluidized bed is presented, and also the results of modeling. Five sizes of ash particles (1.02-1.25; 1.25-1.6; 1.6-2.0; 2.0-5.0; 5.0-10.0 mm) produced in an industrial CFB boiler were examined. A new model of mechanical attrition has been proposed which incorporates new parameters: the shape factor of particles and the ratio of the bed height to bed diameter, strongly influencing the rate of bed mass loss. The model describes very well experimental data for coal-ash particles attrition. The attrition-rate coefficient for ash particles was evaluated.

Attrition and carbon formation on iron catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kohler, S.D.; Harrington, M.S.; Jackson, N.B.

1994-08-01

A serious engineering problem that needs to be addressed in the scale-up of slurry-phase, Fischer-Tropsch reactors is attrition of the precipitated iron catalyst. Attrition, which can break down the catalyst into particles too small to filter, results from both mechanical and chemical forces. This study examines the chemical causes of attrition in iron catalysts. A bench-scale, slurry-phase CSTR is used to simulate operating conditions that lead to attrition of the catalyst. The average particle size and size distribution of the catalyst samples are used to determine the effect of slurry temperature, reducing gas, gas flow rate and time upon attritionmore » of the catalyst. Carbon deposition, a possible contributing factor to attrition, has been examined using gravimetric analysis and TEM. Conditions affecting the rate of carbon deposition have been compared to those leading to attrition of the precipitated iron catalyst.« less

Attritional wear and abrasive surface alterations of composite resin materials in vitro.

PubMed

Göhring, T N; Besek, M J; Schmidlin, P R

2002-01-01

A laboratory study was performed with 232 specimens and 72 human enamel, 24 gold, 24 ceramic and 12 composite antagonists in 22 groups to test attritional and abrasive wear behavior of composite materials compared to wear behavior of human enamel. Belleglass HP, Concept Inlay/Onlay, Targis and Targis Upgrade 99 composite resin for lab-made restorations was tested as well as Tetric Ceram and FHC Merz light as resins for direct restorations. Natural human enamel specimens served as control. All specimens were subjected to long-term thermo-mechanical loading in a computer-controlled masticator, chemical degradation and toothbrush/toothpaste abrasion. Wear of specimen in occlusal contact area (OCA), contact-free occlusal area and wear of natural enamel cusps as well as antagonists made of gold, ceramic and composite in identical form was measured after 120,000, 240,000, 640,000 and 1200,000 load cycles. A qualitative SEM analysis was performed to support quantitative data. Belleglass HP and Targis Upgrade 99 restorative materials showed wear resistance comparable to human enamel when loaded with enamel cusps. Wear of Targis versus composite and gold antagonists was significantly higher (p<0.0001). Analysis of surface alterations showed hygroscopic expansion in all composite resins during the test. As a consequence of this study, necessity to further improve physical properties of composites for long lasting restorations was obvious. Beside of attritional wear in OCA, attention must be given to stable filler-matrix interfaces and prevention of water sorption.

Effects of attrition, prior acid-etching, and cyclic loading on the bond strength of a self-etching adhesive system to dentin.

PubMed

Shinkai, Koichi; Ebihara, Takashi; Shirono, Manabu; Seki, Hideaki; Wakaki, Suguru; Suzuki, Masaya; Suzuki, Shiro; Katoh, Yoshiroh

2009-03-01

The purpose of this study was to evaluate the effects of dentin attrition, phosphoric acid etching, and cyclic loading on the microtensile bond strength (microTBS) of a self-etching adhesive system to dentin. Flat dentin surfaces of human molars were assigned to eight experimental groups based on those with or without attrition, prior acid-etching, and cyclic loading. Resin composite paste was placed and polymerized after the bonding procedure according to manufacturer's instructions. The specimens were subjected to microTBS testing at a crosshead speed of 0.5 mm/min. Results showed that the minimum mean value of microTBS was 14.9 MPa in the group without attrition and acid-etching but with loading, while the maximum mean value of microTBS was 40.0 MPa in the group without attrition and loading but with acid etching. Therefore, the value of microTBS to dentin without attrition was significantly decreased by cyclic loading but that to dentin with attrition was not affected.

The influence of fluoride varnish on the attrition of dentine.

PubMed

Li, H; Watson, T F; Sherriff, M; Curtis, R; Bartlett, D W

2007-01-01

Previous investigations have shown the potential for fluoride to be protective in an abrasion/erosion laboratory model. The aim of this study was to investigate the effect of high concentrations of fluoride delivered in a varnish on attrition of dentine. Fifteen caries-free, intact lower third molar teeth were sectioned and the enamel removed by a water-cooled diamond disc. Polished dentine surfaces were divided into 8 areas, 4 of which were randomly covered with a high-concentration fluoride varnish for 24 h. The samples were subjected to 5,000 cycles of attrition bathed under artificial saliva. Microhardness testing adjacent to the wear scars showed no statistical difference between the fluoride-treated (71.42 KHN, SD 10.52) and control surfaces (72.66 KHN, SD 9.69). The volume of the wear scar was statistically greater for the fluoride-treated surface at 9.6 microm(3) (SD 4.92) and 8.13 microm(3) (SD 5.54) for the control areas (p = 0.029). The low pH of the fluoride varnish appears to have increased the amount of wear from attrition in this laboratory study. Copyright 2007 S. Karger AG, Basel.

DEVELOPMENT OF ATTRITION RESISTANT IRON-BASED FISCHER-TROPSCH CATALYSTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adeyinka A. Adeyiga

2001-09-01

The Fischer-Tropsch (F-T) reaction provides a way of converting coal-derived synthesis gas (CO+H{sub 2}) to liquid fuels. Since the reaction is highly exothermic, one of the major problems in control of the reaction is heat removal. Recent work has shown that the use of slurry bubble column reactors (SBCRs) can largely solve this problem. The use of iron-based catalysts is attractive not only due to their low cost and ready availability, but also due to their high water-gas shift activity which makes it possible to use these catalysts with low H{sub 2}/CO ratios. However, a serious problem with use ofmore » Fe catalysts in a SBCR is their tendency to undergo attrition. This can cause fouling/plugging of downstream filters and equipment, makes the separation of catalyst from the oil/wax product very difficult if not impossible, and results in a steady loss of catalyst from the reactor. Recently, fundamental understanding of physical attrition is being addressed by incorporating suitable binders into the catalyst recipe. This has resulted in the preparation of a spray dried Fe-based catalyst having aps of 70 mm with high attrition resistance. This Fe-based attrition resistant, active and selective catalyst gave 95% CO conversion through 125 hours of testing in a fixed-bed at 270 C, 1.48 MPa, H{sub 2}/CO=0.67 and 2.0 NL/g-cat/h with C{sub 5}{sup +} selectivity of >78% and methane selectivity of <5%. However, further development of the catalyst is needed to address the chemical attrition due to phase changes that any Fe-catalyst goes through potentially causing internal stresses within the particle and resulting in weakening, spalling or cracking. The objective of this research is to develop robust iron-based Fischer-Tropsch catalysts that have suitable activity, selectivity and stability to be used in the slurry bubble column reactor. Specifically we aim to develop to: (i) improve the performance and preparation procedure of the high activity, high attrition resistant, high alpha iron-based catalysts synthesized at Hampton University, (ii) seek improvements in the catalyst performance through variations in process conditions, pretreatment procedures and/or modifications in catalyst preparation steps and (iii) investigate the performance in a slurry reactor. The effort during the reporting period has been devoted to attrition study of the iron-based catalysts. Precipitated silica appeared to decrease attrition resistance of spray-dried iron FT catalysts. It was found that the catalyst with precipitated silica content at around 12wt% showed the lowest attrition resistance. The results of net change in volume moment and catalyst morphology showed supporting evidences to the attrition results. Catalysts with low attrition resistance generated more fines loss, had higher net change in volume moment and showed more breakage of particles. BET surface area and pore volume of this catalyst series fluctuated; therefore no conclusion can be drawn from the data obtained. However, catalyst with no precipitated silica showed the lowest in BET surface area and pore volume, as expected. Addition of precipitated silica to the catalysts had no effect to the phase changes of iron that could have significant influence to catalyst attrition. The presence of precipitated silica is needed for enhancing catalyst surface area; however, the amount of silica added should be compromising with attrition resistance of catalysts.« less

Erosion and attrition of human enamel in vitro part II: influence of time and loading.

PubMed

Eisenburger, M; Addy, M

2002-01-01

To determine the influence of load and time on enamel wear by attrition under neutral and acid environments in vitro. Groups of 10 enamel cusp and smooth surface specimens obtained from unerupted third molars were opposed in a wear machine under loads of 200, 400 and 600 g in citric acid at pH 3.2 and in physiological saline at 35 degrees C for 30 min (2280 wear cycles). The experiment was repeated with a load of 600 g for 10 and 20 min accompanied by 10 taped specimens to measure erosion only. Erosion and attrition of smooth surface specimens was determined by profilometry. At a load of 600 g attrition in saline increased with time from 7.9 microm (SD 3.7 microm) at 10 min, 10.2 microm (SD 4.8 microm) at 20-25.5 microm (SD 9.1 microm) after 30 min and combined attrition/erosion in citric acid from 1.5 microm (SD 0.4 microm) to 2.5 microm (SD 0.9 microm) to 6.0 microm (SD 3.7 microm). At a fixed time of 30 min, attrition in saline was 5.2 microm (SD 3.6 microm) at 200 g and 8.1 microm (SD 1.5 microm) at 400 g and combined attrition/erosion in citric acid 2.8 microm (SD 1.2 microm) and 3.6 microm (SD 0.7 microm). Comparison between both environments revealed significant differences at fixed load at all time points (p < 0.01) and at fixed time between 400 and 600 g (p < 0.01). Load and time significantly influence enamel wear both in acid and neutral conditions but the effects were not linear. Copyright 2002 Elsevier Science Ltd.

Universal characteristics of particle shape evolution by bed-load chipping

PubMed Central

Sipos, András Árpád; Shaw, Sam; Sarti, Giovanni; Domokos, Gábor

2018-01-01

River currents, wind, and waves drive bed-load transport, in which sediment particles collide with each other and Earth’s surface. A generic consequence is impact attrition and rounding of particles as a result of chipping, often referred to in geological literature as abrasion. Recent studies have shown that the rounding of river pebbles can be modeled as diffusion of surface curvature, indicating that geometric aspects of impact attrition are insensitive to details of collisions and material properties. We present data from fluvial, aeolian, and coastal environments and laboratory experiments that suggest a common relation between circularity and mass attrition for particles transported as bed load. Theory and simulations demonstrate that universal characteristics of shape evolution arise because of three constraints: (i) Initial particles are mildly elongated fragments, (ii) particles collide with similarly-sized particles or the bed, and (iii) collision energy is small enough that chipping dominates over fragmentation but large enough that sliding friction is negligible. We show that bed-load transport selects these constraints, providing the foundation to estimate a particle’s attrition rate from its shape alone in most sedimentary environments. These findings may be used to determine the contribution of attrition to downstream fining in rivers and deserts and to infer transport conditions using only images of sediment grains. PMID:29670937

Universal characteristics of particle shape evolution by bed-load chipping.

PubMed

Novák-Szabó, Tímea; Sipos, András Árpád; Shaw, Sam; Bertoni, Duccio; Pozzebon, Alessandro; Grottoli, Edoardo; Sarti, Giovanni; Ciavola, Paolo; Domokos, Gábor; Jerolmack, Douglas J

2018-03-01

River currents, wind, and waves drive bed-load transport, in which sediment particles collide with each other and Earth's surface. A generic consequence is impact attrition and rounding of particles as a result of chipping, often referred to in geological literature as abrasion. Recent studies have shown that the rounding of river pebbles can be modeled as diffusion of surface curvature, indicating that geometric aspects of impact attrition are insensitive to details of collisions and material properties. We present data from fluvial, aeolian, and coastal environments and laboratory experiments that suggest a common relation between circularity and mass attrition for particles transported as bed load. Theory and simulations demonstrate that universal characteristics of shape evolution arise because of three constraints: (i) Initial particles are mildly elongated fragments, (ii) particles collide with similarly-sized particles or the bed, and (iii) collision energy is small enough that chipping dominates over fragmentation but large enough that sliding friction is negligible. We show that bed-load transport selects these constraints, providing the foundation to estimate a particle's attrition rate from its shape alone in most sedimentary environments. These findings may be used to determine the contribution of attrition to downstream fining in rivers and deserts and to infer transport conditions using only images of sediment grains.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Lehao

A nanocrystalline surface layer was produced on Mg-3 wt.% Li-6 wt.% Al alloy by means of surface mechanical attrition treatment (SMAT). Microstructure features of various sections were systematically characterized by transmission electron microscopy. The results indicate that grain refinement induced by SMAT is dominated mainly by dislocation slip. Twinning is active at the early stage of grain refinement process when the grain size is large. The dislocation-dominated deformation mechanism is attributed to the change of c/a ratio due to the alloying of Li in Mg matrix and the suppression of twinning due to grain refinement. Nanoindentation results show that themore » hardness of the surface is enhanced by SMAT. - Highlights: •Nanocrystalline surface layer was produced on Mg-3 wt.%Li-6 wt.%Al alloy by SMAT. •Grain refinement induced by SMAT is dominated mainly by dislocation slip. •Twinning is active at the early stage of grain refinement process. •The hardness of the surface was enhanced by SMAT.« less

Attrition Bias Related to Missing Outcome Data: A Longitudinal Simulation Study.

PubMed

Lewin, Antoine; Brondeel, Ruben; Benmarhnia, Tarik; Thomas, Frédérique; Chaix, Basile

2018-01-01

Most longitudinal studies do not address potential selection biases due to selective attrition. Using empirical data and simulating additional attrition, we investigated the effectiveness of common approaches to handle missing outcome data from attrition in the association between individual education level and change in body mass index (BMI). Using data from the two waves of the French RECORD Cohort Study (N = 7,172), we first examined how inverse probability weighting (IPW) and multiple imputation handled missing outcome data from attrition in the observed data (stage 1). Second, simulating additional missing data in BMI at follow-up under various missing-at-random scenarios, we quantified the impact of attrition and assessed how multiple imputation performed compared to complete case analysis and to a perfectly specified IPW model as a gold standard (stage 2). With the observed data in stage 1, we found an inverse association between individual education and change in BMI, with complete case analysis, as well as with IPW and multiple imputation. When we simulated additional attrition under a missing-at-random pattern (stage 2), the bias increased with the magnitude of selective attrition, and multiple imputation was useless to address it. Our simulations revealed that selective attrition in the outcome heavily biased the association of interest. The present article contributes to raising awareness that for missing outcome data, multiple imputation does not do better than complete case analysis. More effort is thus needed during the design phase to understand attrition mechanisms by collecting information on the reasons for dropout.

Attrition-enhanced sulfur capture by limestone particles in fluidized beds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saastamoinen, J.J.; Shimizu, T.

2007-02-14

Sulfur capture by limestone particles in fluidized beds is a well-established technology. The underlying chemical and physical phenomena of the process have been extensively studied and modeled. However, most of the studies have been focused on the relatively brief initial stage of the process, which extends from a few minutes to hours, yet the residence time of the particles in the boiler is much longer. Following the initial stage, a dense product layer will be formed on the particle surface, which decreases the rate of sulfur capture and the degree of utilization of the sorbent. Attrition can enhance sulfur capturemore » by removing this layer. A particle model for sulfur capture has been incorporated with an attrition model. After the initial stage, the rate of sulfur capture stabilizes, so that attrition removes the surface at the same rate as diffusion and chemical reaction produces new product in a thin surface layer of a particle. An analytical solution for the conversion of particles for this regime is presented. The solution includes the effects of the attrition rate, diffusion, chemical kinetics, pressure, and SO{sub 2} concentration, relative to conversion-dependent diffusivity and the rate of chemical reaction. The particle model results in models that describe the conversion of limestone in both fly ash and bottom ash. These are incorporated with the residence time (or reactor) models to calculate the average conversion of the limestone in fly ash and bottom ash, as well as the efficiency of sulfur capture. Data from a large-scale pressurized fluidized bed are compared with the model results.« less

Modeling equine race surface vertical mechanical behaviors in a musculoskeletal modeling environment.

PubMed

Symons, Jennifer E; Fyhrie, David P; Hawkins, David A; Upadhyaya, Shrinivasa K; Stover, Susan M

2015-02-26

Race surfaces have been associated with the incidence of racehorse musculoskeletal injury, the leading cause of racehorse attrition. Optimal race surface mechanical behaviors that minimize injury risk are unknown. Computational models are an economical method to determine optimal mechanical behaviors. Previously developed equine musculoskeletal models utilized ground reaction floor models designed to simulate a stiff, smooth floor appropriate for a human gait laboratory. Our objective was to develop a computational race surface model (two force-displacement functions, one linear and one nonlinear) that reproduced experimental race surface mechanical behaviors for incorporation in equine musculoskeletal models. Soil impact tests were simulated in a musculoskeletal modeling environment and compared to experimental force and displacement data collected during initial and repeat impacts at two racetracks with differing race surfaces - (i) dirt and (ii) synthetic. Best-fit model coefficients (7 total) were compared between surface types and initial and repeat impacts using a mixed model ANCOVA. Model simulation results closely matched empirical force, displacement and velocity data (Mean R(2)=0.930-0.997). Many model coefficients were statistically different between surface types and impacts. Principal component analysis of model coefficients showed systematic differences based on surface type and impact. In the future, the race surface model may be used in conjunction with previously developed the equine musculoskeletal models to understand the effects of race surface mechanical behaviors on limb dynamics, and determine race surface mechanical behaviors that reduce the incidence of racehorse musculoskeletal injury through modulation of limb dynamics. Copyright © 2015 Elsevier Ltd. All rights reserved.

Toward the existence of ultrafast diffusion paths in Cu with a gradient microstructure: Room temperature diffusion of Ni

NASA Astrophysics Data System (ADS)

Wang, Z. B.; Lu, K.; Wilde, G.; Divinski, S.

2008-09-01

Room temperature diffusion of Ni63 in Cu with a gradient microstructure prepared by surface mechanical attrition treatment (SMAT) was investigated by applying the radiotracer technique. The results reveal significant penetration of Ni into the nanostructured layer. The relevant diffusivity is higher than that along the conventional high-angle grain boundaries by about six orders of magnitude. This behavior is associated with a higher energy state of internal interfaces produced via plastic deformation. The diffusivity in the top surface layer is somewhat smaller than that in the subsurface layer. This fact is related to nanotwin formation in the former during SMAT.

Reciprocal Mentoring Residencies... Better Transitions to Teaching

ERIC Educational Resources Information Center

Paris, Lisa

2010-01-01

The 2007 "Top of the Class" report on the Inquiry into Teacher Education in Australia found teacher induction failure and high attrition rates were endemic in most Australian states. Mentoring was advocated as an important mechanism for countering the debilitating drain attrition exerted on the profession (more than 30% within the first…

Ash production by attrition in volcanic conduits and plumes.

PubMed

Jones, T J; Russell, J K

2017-07-17

Tephra deposits result from explosive volcanic eruption and serve as indirect probes into fragmentation processes operating in subsurface volcanic conduits. Primary magmatic fragmentation creates a population of pyroclasts through volatile-driven decompression during conduit ascent. In this study, we explore the role that secondary fragmentation, specifically attrition, has in transforming primary pyroclasts upon transport in volcanic conduits and plumes. We utilize total grain size distributions from a suite of natural and experimentally produced tephra to show that attrition is likely to occur in all explosive volcanic eruptions. Our experimental results indicate that fine ash production and surface area generation is fast (<15 min) thereby rapidly raising the fractal dimension of tephra deposits. Furthermore, a new metric, the Entropy of Information, is introduced to quantify the degree of attrition (secondary fragmentation) from grain size data. Attrition elevates fine ash production which, in turn, has consequences for eruption column stability, tephra dispersal, aggregation, volcanic lightening generation, and has concomitant effects on aviation safety and Earth's climate.

DEVELOPMENT OF ATTRITION RESISTANT IRON-BASED FISCHER-TROPSCH CATALYSTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adeyinka A. Adeyiga

2003-12-01

Fischer-Tropsch (FT) synthesis to convert syngas (CO + H{sub 2}) derived from natural gas or coal to liquid fuels and wax is a well-established technology. For low H{sub 2} to CO ratio syngas produced from CO{sub 2} reforming of natural gas or from gasification of coal, the use of Fe catalysts is attractive because of their high water gas shift activity in addition to their high FT activity. Fe catalysts are also attractive due to their low cost and low methane selectivity. Because of the highly exothermic nature of the FT reaction, there has been a recent move away frommore » fixed-bed reactors toward the development of slurry bubble column reactors (SBCRs) that employ 30 to 90 {micro}m catalyst particles suspended in a waxy liquid for efficient heat removal. However, the use of Fe FT catalysts in an SBCR has been problematic due to severe catalyst attrition resulting in fines that plug the filter employed to separate the catalyst from the waxy product. Fe catalysts can undergo attrition in SBCRs not only due to vigorous movement and collisions but also due to phase changes that occur during activation and reaction. The objectives of this research were to develop a better understanding of the parameters affecting attrition of Fe F-T catalysts suitable for use in SBCRs and to incorporate this understanding into the design of novel Fe catalysts having superior attrition resistance. The catalysts were prepared by co-precipitation, followed by binder addition and spray drying at 250 C in a 1 m diameter, 2 m tall spray dryer. The binder silica content was varied from 0 to 20 wt %. The results show that use of small amounts of precipitated SiO{sub 2} alone in spray-dried Fe catalysts can result in good attrition resistance. All catalysts investigated with SiO{sub 2} wt% {le} 12 produced fines less than 10 wt% during the jet cup attrition test, making them suitable for long-term use in a slurry bubble column reactor. Thus, concentration rather than type of SiO{sub 2} incorporated into catalyst has a more critical impact on catalyst attrition resistance of spray-dried Fe catalysts. Lower amounts of SiO{sub 2} added to a catalyst give higher particle densities and therefore higher attrition resistances. In order to produce a suitable SBCR catalyst, however, the amount of SiO{sub 2} added has to be optimized to provide adequate surface area, particle density, and attrition resistance. Two of the catalysts with precipitated and binder silica were tested in Texas A&M University's CSTR (Autoclave Engineers). Spray-dried catalysts with compositions 100 Fe/5 Cu/4.2 K/11 (P) SiO{sub 2} and 100 Fe/5 Cu/4.2 K/1.1 (B) SiO{sub 2} have excellent selectivity characteristics (low methane and high C{sub 5}{sup +} yields), but their productivity and stability (deactivation rate) need to be improved. Mechanical integrity (attrition strength) of these two catalysts was markedly dependent upon their morphological features. The attrition strength of the catalyst made out of largely spherical particles (1.1 (B) SiO{sub 2}) was considerably higher than that of the catalyst consisting of irregularly shaped particles (11 (P) SiO{sub 2}).« less

Surface-Sensitive Microwear Texture Analysis of Attrition and Erosion.

PubMed

Ranjitkar, S; Turan, A; Mann, C; Gully, G A; Marsman, M; Edwards, S; Kaidonis, J A; Hall, C; Lekkas, D; Wetselaar, P; Brook, A H; Lobbezoo, F; Townsend, G C

2017-03-01

Scale-sensitive fractal analysis of high-resolution 3-dimensional surface reconstructions of wear patterns has advanced our knowledge in evolutionary biology, and has opened up opportunities for translatory applications in clinical practice. To elucidate the microwear characteristics of attrition and erosion in worn natural teeth, we scanned 50 extracted human teeth using a confocal profiler at a high optical resolution (X-Y, 0.17 µm; Z < 3 nm). Our hypothesis was that microwear complexity would be greater in erosion and that anisotropy would be greater in attrition. The teeth were divided into 4 groups, including 2 wear types (attrition and erosion) and 2 locations (anterior and posterior teeth; n = 12 for each anterior group, n = 13 for each posterior group) for 2 tissue types (enamel and dentine). The raw 3-dimensional data cloud was subjected to a newly developed rigorous standardization technique to reduce interscanner variability as well as to filter anomalous scanning data. Linear mixed effects (regression) analyses conducted separately for the dependent variables, complexity and anisotropy, showed the following effects of the independent variables: significant interactions between wear type and tissue type ( P = 0.0157 and P = 0.0003, respectively) and significant effects of location ( P < 0.0001 and P = 0.0035, respectively). There were significant associations between complexity and anisotropy when the dependent variable was either complexity ( P = 0.0003) or anisotropy ( P = 0.0014). Our findings of greater complexity in erosion and greater anisotropy in attrition confirm our hypothesis. The greatest geometric means were noted in dentine erosion for complexity and dentine attrition for anisotropy. Dentine also exhibited microwear characteristics that were more consistent with wear types than enamel. Overall, our findings could complement macrowear assessment in dental clinical practice and research and could assist in the early detection and management of pathologic tooth wear.

Effect of attrition milling on the reaction sintering of silicon nitride

NASA Technical Reports Server (NTRS)

Herbell, T. P.; Glasgow, T. K.; Yeh, H. C.

1978-01-01

Silicon powder was ground in a steel attrition mill under nitrogen. Air exposed powder was compacted, prefired in helium, and reaction sintered in nitrogen-4 v/o hydrogen. For longer grinding times, oxygen content, surface area and compactability of the powder increased; and both alpha/beta ratio and degreee of nitridation during sintering increased. Iron content remained constant.

Effect of attrition milling on the reaction sintering of silicon nitride

NASA Technical Reports Server (NTRS)

Herbell, T. P.; Glasgow, T. K.; Yeh, H. C.

1978-01-01

Silicon powder was ground in a steel attrition mill under nitrogen. Air-exposed powder was compacted, prefired in helium, and reaction-sintered in nitrogen-4 v/o hydrogen. For longer grinding times, oxygen content, surface area and compactability of the powder increased; and both alpha/beta ratio and degree of nitridation during sintering increased. Iron content remained constant.

The role of erosion, abrasion and attrition in tooth wear.

PubMed

Barbour, Michele E; Rees, Gareth D

2006-01-01

There is increasing clinical awareness of erosion of enamel and dentine by dietary acids and the consequent increased susceptibility to physical wear. Enamel erosion is characterized by acid-mediated surface softening that, if unchecked, will progress to irreversible loss of surface tissue, potentially exposing the underlying dentine. In comparison, dentine erosion is less well understood as the composition and microstructure are more heterogeneous. Factors which affect the erosive potential of a solution include pH, titratable acidity, common ion concentrations, and frequency and method of exposure. Abrasion and attrition are sources of physical wear and are commonly associated with tooth brushing and tooth-to-tooth contact, respectively. A combination of erosion and abrasion or attrition exacerbates wear; however, further research is required to understand the role of fluoride in protecting mineralized tissues from such processes. Abrasive wear may be seen in a wide range of patients, whereas attritive loss is usually seen in individuals with bruxism. Wear processes are implicated in the development of dentine hypersensitivity. Saliva confers the major protective function against wear due to its role in pellicle formation, buffering, acid clearance, and hard tissue remineralization. This review focuses on the physiochemical factors impacting tooth wear.

Attrition of Women Business Majors in an Urban Community College.

ERIC Educational Resources Information Center

Karlen, Janice M.

2004-01-01

Identified intervention protocols that could help reduce the attrition of women business majors at an urban community college. Review of academic progress data and data from student surveys which examined students' reasons for leaving the institution indicated that there was a need for support mechanisms throughout the freshman year and extending…

Attrition of fluid cracking catalyst in fluidized beds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boerefijn, R.; Ghadiri, M.

1996-12-31

Particle attrition in fluid catalytic cracking units causes loss of catalyst, which could amount to a few tonnes per day! The dependence of attrition on the process conditions and catalyst properties is therefore of great industrial interest, but it is however not well established at present. The process of attrition in the jetting area of fluidised beds is addressed and the attrition test method of Forsythe & Hertwig is analysed in this paper. This method is used commonly to assess the attrition propensity of FCC powder, whereby the attrition rate in a single jet at very high orifice velocity (300more » m s{sup -1}) is measured. There has been some concern on the relevance of this method to attrition in FCC units. Therefore, a previously-developed model of attrition in the jetting region is employed in an attempt to establish a solid basis of interpretation of the Forsythe & Hertwig test and its application as an industrial standard test. The model consists of two parts. The first part predicts the solids flow patterns in the jet region, simulating numerically the Forsythe & Hertwig test. The second part models the breakage of single particles upon impact. Combining these two models, thus linking single particle mechanical properties to macroscopic flow phenomena, results in the modelling of the attrition rate of particles entrained into a single high speed jet. High speed video recordings are made of a single jet in a two-dimensional fluidised bed, at up to 40500 frames per second, in order to quantify some of the model parameters. Digital analysis of the video images yields values for particle velocities and entrainment rates in the jet, which can be compared to model predictions. 15 refs., 8 figs.« less

Decision-making, sensitivity to reward, and attrition in weight-management

PubMed Central

Koritzky, Gilly; Dieterle, Camille; Rice, Chantelle; Jordan, Katie; Bechara, Antoine

2014-01-01

Objective Attrition is a common problem in weight-management. Understanding the risk factors for attrition should enhance professionals’ ability to increase completion rates and improve health outcomes for more individuals. We propose a model that draws upon neuropsychological knowledge on reward-sensitivity in obesity and overeating to predict attrition. Design & Methods 52 participants in a weight-management program completed a complex decision-making task.Decision-making characteristics – including sensitivity to reward – were further estimated using a quantitative model. Impulsivity and risk-taking measures were also administered. Results Consistent with the hypothesis that sensitivity to reward predicted attrition, program dropouts had higher sensitivity to reward than completers (p < 0.03). No differences were observed between completers and dropouts in initial BMI, age, employment status, or the number of prior weight-loss attempts (p ≥ 0.07). Completers had a slightly higher education level than dropouts, but its inclusion in the model did not increase predictive power. Impulsivity, delay of gratification, and risk-taking did not predict attrition, either. Conclusions Findings link attrition in weight-management to the neural mechanisms associated with reward-seeking and related influences on decision-making. Individual differences in the magnitude of response elicited by rewards may account for the relative difficulty experienced by dieters in adhering to treatment. PMID:24771588

The prevalence, aetiology and clinical appearance of tooth wear: the Nigerian experience.

PubMed

Oginni, O; Olusile, A O

2002-08-01

To establish the prevalence and severity of tooth wear among Nigerians and to compare the pattern and aetiology with findings of earlier studies in Western populations. Clinical examinations for tooth wear using the tooth wear index (TWI). The Federal Republic of Nigeria. Patients attending the Dental Hospital, Obafemi Awolowo University Teaching Hospital's Complex Ile-Ife. Attrition, abrasion and erosion. Of the 126 patients with tooth wear 81 had attrition, 20 had abrasion, 9 had erosion and 16 had attrition and abrasion combined. A total of 15,480 tooth surfaces were examined. 2,229 (14.4%) surfaces had tooth wear out of which 1,007 (6.5%) were pathologically worn down. The frequency of tooth wear increased with the age of patients. Most of the pathologically worn surfaces were just one point above maximum acceptable value. The aetiological factors associated with tooth wear are not different from those encountered in Western cultures but the pattern of wear differs. Pathological tooth wear presents as an age related phenomenon and is probably more severe in Nigerians.

Evaluation of composite wear with a new multi-mode oral wear simulator.

PubMed

Condon, J R; Ferracane, J L

1996-07-01

The goals of this study were to develop a machine which simultaneously produces wear through the two main oral wear mechanisms of abrasion and attrition by the action of an enamel antagonist and to compare the results obtained for dental composites using this machine to those obtained from clinical studies and other in vitro studies. The accuracy of this new wear tester was determined by examining 11 commercial composite filling materials and 1 amalgam. Specimens were subjected to three-body abrasion and attrition wear for 50,000 cycles. Profilometry was used to quantitate wear of the composites. Linear regression analysis was used to correlate the results to those obtained from clinical studies, as well as from other in vitro wear testers. The area of enamel wear was also determined by image analysis. The SEM was used to evaluate the wear surfaces. The lowest abrasion wear was recorded for the amalgam and for the microfill and smaller-particle composites. Attrition wear was enhanced for the microfill composites and one small-particle hybrid. There was a strong correlation between the results obtained with the new wear tester and those obtained in the clinical trials cited in the literature. Wear of the enamel antagonist was the greatest for the composites with the largest particle sizes. The wear tester showed a reasonable correlation with other wear-producing machines. A new wear tester developed to evaluate and discriminate abrasion and attrition wear provided results similar to those reported in the literature for a variety of commercial composites. The new machine is capable of characterizing the behavior of a material in multiple wear modes simultaneously with one simple, realistic test.

Toothbrush abrasion, simulated tongue friction and attrition of eroded bovine enamel in vitro.

PubMed

Vieira, A; Overweg, E; Ruben, J L; Huysmans, M C D N J M

2006-05-01

Enamel erosion results in the formation of a softened layer that is susceptible to disruption by mechanical factors such as brushing abrasion, tongue friction and attrition. The aim of this study was to investigate the individual contribution of those mechanical insults to the enamel loss caused by dental erosion. Forty two bovine enamel samples were randomly divided into seven groups (n=6 per group) that were submitted to 3cycles of one of the following regimes: erosion and remineralization (er/remin); toothbrush abrasion and remineralization (abr/remin); erosion, toothbrush abrasion and remineralization (er/abr/remin); attrition and remineralization (at/remin); erosion, attrition and remineralization (er/at/remin); simulated tongue friction and remineralization (tg/remin); erosion, simulated tongue friction and remineralization (er/tg/remin). Erosion took place in a demineralization solution (50mM citric acid, pH 3) for 10min under agitation. Brushing abrasion, tongue friction and attrition were simulated for 1min using a home-made wear device. Remineralization was carried out in artificial saliva for 2h. Enamel loss was quantified using optical profilometry. One-way ANOVA indicated a significant difference between the amounts of enamel lost due to the different wear regimes (p

Stress-corrosion behavior of aluminum-lithium alloys in aqueous salt environments

NASA Technical Reports Server (NTRS)

Pizzo, P. P.; Galvin, R. P.; Nelson, H. G.

1984-01-01

The stress corrosion susceptibility of two powder metallurgy (P/M) alloys, Al-Li-Cu and Al-Li-Cu-Mg; two mechanically attrited (M/A) alloys, Al-Li-Cu and Al-Li-Mg; and two wrought, ingot alloys, X-2020 and AA7475, are compared. Time-dependent fracture in an aqueous sodium chloride environment under alternate immersion condition was found to vary significantly between alloys. The stress corrosion behavior of the two powder metallurgy processed alloys was studied in detail under conditions of crack initiation, static crack growth, and fatigue crack growth. A variety of stress corrosion tests were performed including smooth surface, time-to-failure tests; potentiostatic tests on smooth surfaces exposed to constant applied strain rates; and fracture mechanics-type tests under static and cyclic loads. Both alloys show surface pitting and subsequent intergranular corrosion. Pitting is more severe in the magnesium-bearing alloy and is associated with stringer particles strung along the extrusion direction as a result of P/M processing.

Stress-corrosion behavior of aluminum-lithium alloys in aqueous environments

NASA Technical Reports Server (NTRS)

Pizzo, P. P.; Galvin, R. P.; Nelson, H. G.

1983-01-01

The stress corrosion susceptibility of two powder metallurgy (P/M) alloys, Al-Li-Cu and Al-Li-Cu-Mg two mechanically attrited (M/A) alloys, Al-Li-Cu and Al-Li-Mg; and two wrought, ingot alloys, X-2020 and AA7475, are compared. Time-dependent fracture in an aqueous sodium chloride environment under alternate immersion condition was found to vary significantly between alloys. The stress corrosion behavior of the two powder metallurgy processed alloys was studied in detail under conditions of crack initiation, static crack growth, and fatigue crack growth. A variety of stress corrosion tests were performed including smooth surface, time-to-failure tests; potentiostatic tests on smooth surfaces exposed to constant applied strain rates; and fracture mechanics-type tests under static and cyclic loads. Both alloys show surface pitting and subsequent intergranular corrosion. Pitting is more severe in the magnesium-bearing alloy and is associated with stringer particles strung along the extrusion direction as a result of P/M processing.

Attrition and changes in size distribution of lime sorbents during fluidization in a circulating fluidized bed absorber. Double quarterly report, January 1--August 31, 1993

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Sang-Kwun; Keener, T.C.; Cook, J.L.

1993-12-31

The experimental data of lime sorbent attrition obtained from attriton tests in a circulating fluidized bed absorber (CFBA) are represented. The results are interpreted as both the weight-based attrition rate and size-based attrition rate. The weight-based attrition rate constants are obtained from a modified second-order attrition model, incorporating a minimum fluidization weight, W{sub min}, and excess velocity. Furthermore, this minimum fluidization weight, or W{sub min} was found to be a function of both particle size and velocity. A plot of the natural log of the overall weight-based attrition rate constants (ln K{sub a}) for Lime 1 (903 MMD) at superficialmore » gas velocities of 2 m/s, 2.35 m/s, and 2.69 m/s and for Lime 2 (1764 MMD) at superficial gas velocities of 2 m/s, 3 m/s, 4 m/s and 5 m/s versus the energy term, 1/(U-U{sub mf}){sup 2}, yielded a linear relationship. And, a regression coefficient of 0.9386 for the linear regression confirms that K{sub a} may be expressed in Arrhenius form. In addition, an unsteady state population model is represented to predict the changes in size distribution of bed materials during fluidization. The unsteady state population model was verified experimentally and the solid size distribution predicted by the model agreed well with the corresponding experimental size distributions. The model may be applicable for the batch and continuous operations of fluidized beds in which the solids size reduction is predominantly resulted from attritions and elutriations. Such significance of the mechanical attrition and elutriation is frequently seen in a fast fluidized bed as well as in a circulating fluidized bed.« less

Ultralow nanoscale wear through atom-by-atom attrition in silicon-containing diamond-like carbon

NASA Astrophysics Data System (ADS)

Bhaskaran, Harish; Gotsmann, Bernd; Sebastian, Abu; Drechsler, Ute; Lantz, Mark A.; Despont, Michel; Jaroenapibal, Papot; Carpick, Robert W.; Chen, Yun; Sridharan, Kumar

2010-03-01

Understanding friction and wear at the nanoscale is important for many applications that involve nanoscale components sliding on a surface, such as nanolithography, nanometrology and nanomanufacturing. Defects, cracks and other phenomena that influence material strength and wear at macroscopic scales are less important at the nanoscale, which is why nanowires can, for example, show higher strengths than bulk samples. The contact area between the materials must also be described differently at the nanoscale. Diamond-like carbon is routinely used as a surface coating in applications that require low friction and wear because it is resistant to wear at the macroscale, but there has been considerable debate about the wear mechanisms of diamond-like carbon at the nanoscale because it is difficult to fabricate diamond-like carbon structures with nanoscale fidelity. Here, we demonstrate the batch fabrication of ultrasharp diamond-like carbon tips that contain significant amounts of silicon on silicon microcantilevers for use in atomic force microscopy. This material is known to possess low friction in humid conditions, and we find that, at the nanoscale, it is three orders of magnitude more wear-resistant than silicon under ambient conditions. A wear rate of one atom per micrometre of sliding on SiO2 is demonstrated. We find that the classical wear law of Archard does not hold at the nanoscale; instead, atom-by-atom attrition dominates the wear mechanisms at these length scales. We estimate that the effective energy barrier for the removal of a single atom is ~1 eV, with an effective activation volume of ~1 × 10-28 m.

Network pharmacology: reigning in drug attrition?

PubMed

Alian, Osama M; Shah, Minjel; Mohammad, Momin; Mohammad, Ramzi M

2013-06-01

In the process of drug development, there has been an exceptionally high attrition rate in oncological compounds entering late phases of testing. This has seen a concurrent reduction in approved NCEs (new chemical entities) reaching patients. Network pharmacology has become a valuable tool in understanding the fine details of drug-target interactions as well as painting a more practical picture of phenotype relationships to patients and drugs. By utilizing all the tools achieved through molecular medicine and combining it with high throughput data analysis, interactions and mechanisms can be elucidated and treatments reasonably tailored to patients expressing specific phenotypes (or genotypes) of disease, essentially reigning in the phenomenon of drug attrition.

Attrition Rate of Oxygen Carriers in Chemical Looping Combustion Systems

NASA Astrophysics Data System (ADS)

Feilen, Harry Martin

This project developed an evaluation methodology for determining, accurately and rapidly, the attrition resistance of oxygen carrier materials used in chemical looping technologies. Existing test protocols, to evaluate attrition resistance of granular materials, are conducted under non-reactive and ambient temperature conditions. They do not accurately reflect the actual behavior under the unique process conditions of chemical looping, including high temperatures and cyclic operation between oxidizing and reducing atmospheres. This project developed a test method and equipment that represented a significant improvement over existing protocols. Experimental results obtained from this project have shown that hematite exhibits different modes of attrition, including both due to mechanical stresses and due to structural changes in the particles due to chemical reaction at high temperature. The test methodology has also proven effective in providing reactivity changes of the material with continued use, a property, which in addition to attrition, determines material life. Consumption/replacement cost due to attrition or loss of reactivity is a critical factor in the economic application of the chemical looping technology. This test method will allow rapid evaluation of a wide range of materials that are best suited for this technology. The most important anticipated public benefit of this project is the acceleration of the development of chemical looping technology for lowering greenhouse gas emissions from fossil fuel combustion.

High-rate squeezing process of bulk metallic glasses

PubMed Central

Fan, Jitang

2017-01-01

High-rate squeezing process of bulk metallic glasses from a cylinder into an intact sheet achieved by impact loading is investigated. Such a large deformation is caused by plastic flow, accompanied with geometrical confinement, shear banding/slipping, thermo softening, melting and joining. Temperature rise during the high-rate squeezing process makes a main effect. The inherent mechanisms are illustrated. Like high-pressure torsion (HPT), equal channel angular pressing (ECAP) and surface mechanical attrition treatments (SMAT) for refining grain of metals, High-Rate Squeezing (HRS), as a multiple-functions technique, not only creates a new road of processing metallic glasses and other metallic alloys for developing advanced materials, but also directs a novel technology of processing, grain refining, coating, welding and so on for treating materials. PMID:28338092

High-rate squeezing process of bulk metallic glasses

NASA Astrophysics Data System (ADS)

Fan, Jitang

2017-03-01

High-rate squeezing process of bulk metallic glasses from a cylinder into an intact sheet achieved by impact loading is investigated. Such a large deformation is caused by plastic flow, accompanied with geometrical confinement, shear banding/slipping, thermo softening, melting and joining. Temperature rise during the high-rate squeezing process makes a main effect. The inherent mechanisms are illustrated. Like high-pressure torsion (HPT), equal channel angular pressing (ECAP) and surface mechanical attrition treatments (SMAT) for refining grain of metals, High-Rate Squeezing (HRS), as a multiple-functions technique, not only creates a new road of processing metallic glasses and other metallic alloys for developing advanced materials, but also directs a novel technology of processing, grain refining, coating, welding and so on for treating materials.

High-rate squeezing process of bulk metallic glasses.

PubMed

Fan, Jitang

2017-03-24

High-rate squeezing process of bulk metallic glasses from a cylinder into an intact sheet achieved by impact loading is investigated. Such a large deformation is caused by plastic flow, accompanied with geometrical confinement, shear banding/slipping, thermo softening, melting and joining. Temperature rise during the high-rate squeezing process makes a main effect. The inherent mechanisms are illustrated. Like high-pressure torsion (HPT), equal channel angular pressing (ECAP) and surface mechanical attrition treatments (SMAT) for refining grain of metals, High-Rate Squeezing (HRS), as a multiple-functions technique, not only creates a new road of processing metallic glasses and other metallic alloys for developing advanced materials, but also directs a novel technology of processing, grain refining, coating, welding and so on for treating materials.

Improve oxidation resistance at high temperature by nanocrystalline surface layer

NASA Astrophysics Data System (ADS)

Xia, Z. X.; Zhang, C.; Huang, X. F.; Liu, W. B.; Yang, Z. G.

2015-08-01

An interesting change of scale sequence occurred during oxidation of nanocrystalline surface layer by means of a surface mechanical attrition treatment. The three-layer oxide structure from the surface towards the matrix is Fe3O4, spinel FeCr2O4 and corundum (Fe,Cr)2O3, which is different from the typical two-layer scale consisted of an Fe3O4 outer layer and an FeCr2O4 inner layer in conventional P91 steel. The diffusivity of Cr, Fe and O is enhanced concurrently in the nanocrystalline surface layer, which causes the fast oxidation in the initial oxidation stage. The formation of (Fe,Cr)2O3 inner layer would inhabit fast diffusion of alloy elements in the nanocrystalline surface layer of P91 steel in the later oxidation stage, and it causes a decrease in the parabolic oxidation rate compared with conventional specimens. This study provides a novel approach to improve the oxidation resistance of heat resistant steel without changing its Cr content.

Wear particles of single-crystal silicon carbide in vacuum

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1980-01-01

Sliding friction experiments, conducted in vacuum with silicon carbide /000/ surface in contact with iron based binary alloys are described. Multiangular and spherical wear particles of silicon carbide are observed as a result of multipass sliding. The multiangular particles are produced by primary and secondary cracking of cleavage planes /000/, /10(-1)0/, and /11(-2)0/ under the Hertzian stress field or local inelastic deformation zone. The spherical particles may be produced by two mechanisms: (1) a penny shaped fracture along the circular stress trajectories under the local inelastic deformation zone, and (2) attrition of wear particles.

Confusing similar words: ERP correlates of lexical-semantic processing in first language attrition and late second language acquisition.

PubMed

Kasparian, Kristina; Steinhauer, Karsten

2016-12-01

First language (L1) attrition is a socio-linguistic circumstance where second language (L2) learning coincides with changes in exposure and use of the native-L1. Attriters often report experiencing a decline in automaticity or proficiency in their L1 after a prolonged period in the L2 environment, while their L2 proficiency continues to strengthen. Investigating the neurocognitive correlates of attrition alongside those of late L2 acquisition addresses the question of whether the brain mechanisms underlying both L1 and L2 processing are strongly determined by proficiency, irrespective of whether the language was acquired from birth or in adulthood. Using event-related-potentials (ERPs), we examined lexical-semantic processing in Italian L1 attriters, compared to adult Italian L2 learners and to Italian monolingual native speakers. We contrasted the processing of classical lexical-semantic violations (Mismatch condition) with sentences that were equally semantically implausible but arguably trickier, as the target-noun was "swapped" with an orthographic neighbor that differed only in its final vowel and gender-marking morpheme (e.g., cappello (hat) vs. cappella (chapel)). Our aim was to determine whether sentences with such "confusable nouns" (Swap condition) would be processed as semantically correct by late L2 learners and L1 attriters, especially for those individuals with lower Italian proficiency scores. We found that lower-proficiency Italian speakers did not show significant N400 effects for Swap violations relative to correct sentences, regardless of whether Italian was the L1 or the L2. Crucially, N400 response profiles followed a continuum of "nativelikeness" predicted by Italian proficiency scores - high-proficiency attriters and high-proficiency Italian learners were indistinguishable from native controls, whereas attriters and L2 learners in the lower-proficiency range showed significantly reduced N400 effects for "Swap" errors. Importantly, attriters and late L2 learners did not differ in their N400 responses when they belonged to the same proficiency subgroup. Attriters also showed an enhanced P600 response to both kinds of lexical-semantic anomalies, which we discuss as reflecting increased conflict-monitoring and conscious "second thought" processes specifically in attriters. Our findings provide some of the first ERP evidence of attrition effects, and are compatible with accounts of ongoing neuroplasticity for language in adulthood. Proficiency, rather than age-of-acquisition, seems to be the key factor in modulating certain neurocognitive responses, not only within L2 learners but also in L1 attriters. Copyright © 2016 Elsevier Ltd. All rights reserved.

Surface modification and its role in the preparation of FeSi gradient alloys with good magnetic property and ductility

NASA Astrophysics Data System (ADS)

Yu, Haiyuan; Bi, Xiaofang

2018-04-01

Realization of the effective Si penetration at a lower processing temperature is a challenge, but of significance in reducing the strict requirements for the equipment and realizing cost-cutting in production. In this work, we have modified the surface microstructure of Fe-3 wt%Si alloy by using surface mechanical attrition treatment. The modified surface microstructure is characteristic of nanocrystalline, which is found to significantly enhance the efficiency of subsequent Si penetration into the alloy, and successively leading to the decrease of penetration temperature up to 200 °C. As a consequence, the Si gradient distribution across thickness can be readily controlled by changing penetration time, and FeSi alloys with various gradients are prepared by chemical vapor deposition along with subsequent annealing process. The dependence of magnetic and mechanical properties on Si gradient for demonstrates that the increase of Si gradient reduces core losses, especially at higher frequencies, and meanwhile improves ductility of FeSi alloys as well. The mechanism underlying the effect of Si gradient is clarified by combining magnetostriction measurement and domain structure observations. This work provides a facile and effective way for achieving gradient FeSi alloys with good magnetic property and ductility.

Adhesion and abrasion of surface materials in the Venusian aeolian environment

NASA Technical Reports Server (NTRS)

Marshall, John R.; Greeley, Ronald; Tucker, David; Fogleman, Guy; Hixon, Raymond

1991-01-01

In laboratory simulations of the Venusian environment, rock and mineral 'target' surfaces struck by aeolian particles develop a thin layer of accretionary material derived from the particles' attrition debris. Accretion may be (in part) a manifestation of 'cold welding', a process well known in engineering, where bonding occurs between metals at a tribological interface. Accretion on geological materials was found to occur at all Venusian surface temperatures and for all types of materials tested. First-order variations in the amount deposited by particles are related to relative attrition susceptibilities. Second-order variations relate to properties of the particle-target interface. Variations in accretion volume are apparently independent of mineral chemistry and are only weakly dependent on crystallography. The results suggest that accretion should be a fairly universal phenomenon in areas of Venus subject to aeolian activity.

Diagnosis and management of dental wear.

PubMed

Harpenau, Lisa A; Noble, Warden H; Kao, Richard T

2011-04-01

Dental wear is loss of tooth structure resulting from erosion, attrition, abrasion, and, possibly, abfraction. Clinical/experimental data suggest no single damaging mechanism but rather simultaneous interaction of these destructive processes. The most important interaction is abrasion/attrition potentiated by dental erosion. Awareness of this pathosis is not well-appreciated by the public and dental professionals because the signs may be subtle. This article focuses on the recognition, diagnosis, and management of dental wear.

Mechanical Properties of Gradient Structure Mg Alloy

NASA Astrophysics Data System (ADS)

Chen, Hongliang; Yang, Jiang; Zhou, Hao; Moering, Jordan; Yin, Zhe; Gong, Yulan; Zhao, KunYu

2017-09-01

In this work, a surface mechanical attrition treatment (SMAT) process was applied to AZ31B magnesium alloy at room temperature. This method produced a gradient structure on the treated AZ31B, in which the grains of the topmost layer are refined to nanoscale sizes. A combination of nanocrystallites at the surface and coarse-grains in the center are the main features of this structure. This structure results in an excellent combination of both strength and ductility. The highest yield strength for the 30 minutes SMAT AZ31B samples increased to 249 ± 5 MPa and the uniform elongation decreased to 9.3 ± 0.8 pct, whereas the original yield strength was only 147 ± 4 MPa and the uniform elongation was 15.4 ± 1.1 pct. Microstructural observations, stress relaxation tests, and hardness tests were used to verify the results. Additionally, there is a specific volume fraction of gradient structure to achieve the best mechanical performance, which is shown to be in the range of 9.3 to 14 pct for the AZ31B alloy.

Effect of nanostructured titanium on anodization growth of self-organized TiO2 nanotubes

NASA Astrophysics Data System (ADS)

Zhang, Lan; Han, Yong

2010-02-01

To understand the effect of substrate microstructure on the formation of TiO2 nanotubes, anodic oxidizations of commercially pure titanium subjected to surface mechanical attrition treatment (SMATed-Ti) and unSMATed-Ti in a glycol solution containing NH4F and small amounts of water were investigated. The SMATed-Ti exhibit a nanocrystallized surface layer containing a high density of grain boundaries compared with unSMATed-Ti. The anodization results show that the formed TiO2 nanotube layer on the SMATed-Ti is much thicker than that on the unSMATed-Ti. It is indicated that nanocrystallized Ti is propitious to the growth of TiO2 nanotubes; grain boundaries and dislocations play the leading role in accelerating the reaction rate and ion diffusion coefficient during anodization. In addition, nanocrystallization of Ti does not change surface morphologies and phase components of the TiO2 nanotubes.

Attrition Resistant Iron-Based Catalysts For F-T SBCRs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adeyinka A. Adeyiga

2006-01-31

The Fischer-Tropsch (F-T) reaction provides a way of converting coal-derived synthesis gas (CO+ H{sub 2}) to liquid fuels. Since the reaction is highly exothermic, one of the major problems in control of the reaction is heat removal. Recent work has shown that the use of slurry bubble column reactors (SBCRs) can largely solve this problem. The use of iron-(FE) based catalysts is attractive not only due to their low cost and ready availability, but also due to their high water-gas shift activity which makes it possible to use these catalysts with low H{sub 2}/CO ratios. However, a serious problem withmore » the use of Fe catalysts in a SBCR is their tendency to undergo attrition. This can cause fouling/plugging of downstream filters and equipment; makes the separation of catalyst from the oil/wax product very difficult, if not impossible; and results in a steady loss of catalyst from the reactor. Under a previous Department of Energy (DOE)/University Research Grant (UCR) grant, Hampton University reported, for the first time, the development of demonstrably attrition-resistant Fe F-T synthesis catalysts having good activity, selectivity, and attrition resistance. These catalysts were prepared by spray drying Fe catalysts with potassium (K), copper (Cu), and silica (SiO{sub 2}) as promoters. SiO{sub 2} was also used as a binder for spray drying. These catalysts were tested for activity and selectivity in a laboratory-scale fixed-bed reactor. Fundamental understanding of attrition is being addressed by incorporating suitable binders into the catalyst recipe. This has resulted in the preparation of a spray dried HPR-43 catalyst having average particle size (aps) of 70 {micro}m with high attrition resistance. This HPR-43 attrition resistant, active and selective catalyst gave 95% CO conversion through 125 hours of testing in a fixed-bed at 270 C, 1.48 MPa, H{sub 2}/CO=0.67 and 2.0 NL/g-cat/h with C{sub 5+} selectivity of >78% and methane selectivity of less than 5% at an {alpha} of 0.9. Research is proposed to enable further development and optimization of these catalysts by (1) better understanding the role and interrelationship of various catalyst composition and preparation parameters on attrition resistance, activity, and selectivity of these catalysts, (2) the presence of sulfide ions on a precipitated iron catalyst, and (3) the effect of water on sulfided iron F-T catalysts for its activity, selectivity, and attrition. Catalyst preparations will be based on spray drying. The research employed, among other measurements, attrition testing and F-T synthesis at high pressure. Catalyst activity and selectivity is evaluated using a small fixed-bed reactor and a continuous stirred tank reactor (CSTR). The catalysts were prepared by co-precipitation, followed by binder addition and spray drying at 250 C in a 1-m-diameter, 2-m-tall spray dryer. The binder silica content was varied from 0 to 20 wt%. The results show that the use of small amounts of precipitated SiO{sub 2} alone in spray-dried Fe catalysts can result in good attrition resistance. All catalysts investigated with SiO2 wt% {le} 12 produced fines less than 10 wt% during the jet cup attrition test, making them suitable for long-term use in a slurry bubble column reactor. Thus, concentration rather than the type of SiO{sub 2} incorporated into catalyst has a more critical impact on catalyst attrition resistance of spray-dried Fe catalysts. Lower amounts of SiO{sub 2} added to a catalyst give higher particle densities and therefore higher attrition resistances. In order to produce a suitable SBCR catalyst, however, the amount of SiO{sub 2} added has to be optimized to provide adequate surface area, particle density, and attrition resistance. Two of the catalysts with precipitated and binder silica were tested in Texas A&M University's CSTR (Autoclave Engineers). The two catalysts were also tested at The Center for Applied Energy Research in Lexington, Kentucky of the University of Kentucky. Spray-dried catalysts with compositions 100 Fe/5 Cu/4.2 K/11 (P) SiO{sub 2} and 100 Fe/5 Cu/4.2 K/1.1 (B) SiO{sub 2} have excellent selectivity characteristics (low methane and high C{sub 5+} yields), but their productivity and stability (deactivation rate) need to be improved. Mechanical integrity (attrition strength) of these two catalysts was markedly dependent upon their morphological features. The attrition strength of the catalyst made out of largely spherical particles (1.1 (B) SiO{sub 2}) was considerably higher than that of the catalyst consisting of irregularly shaped particles (11 (P) SiO{sub 2}).« less

Dental studies of a Finnish skeletal material: a paleopathologic approach.

PubMed

Varrela, J; Varrela, T M

1991-05-01

This paper reviews a series of paleo-pathologic studies made to investigate associations between dietary factors and development of occlusion, periodontal diseases and caries. The findings indicate that the change from hard to soft food, which has taken place during the last few hundred years, influences occlusion, craniofacial structures and oral health in several ways. Comparative studies show that the frequency of malocclusion has increased substantially. In the same time, a number of alterations have taken place in the morphology of the craniofacial skeleton. The results support the hypothesis that masticatory stress is a regulative factor in craniofacial growth and occlusal development. With soft food and low masticatory activity, jaw growth is not adequate for optimal occlusal development. Approximal wear itself, caused by the attritive diet, seems to be only a minor adjustive factor. Because of the occlusal wear, the crown height decreased with age and the teeth continued to erupt. As a result, root surfaces were exposed. This process has been equated with bone loss but the lack of inflammatory changes on the bone surface indicates that the alveolar bone was not affected by periodontal diseases. This suggests that the alveolar height was maintained at a constant level throughout life and no growth nor resorption took normally place at the crest. Only the exposure of the furcations increased the occurrence of periodontitis. The caries frequency was decreased by mechanical cleaning effect of attritive food but increased by exposure of the root surfaces. Furthermore, the oral microflora may have been modified by factors related to the chemical and physical properties of the diet.

New insights gained on mechanisms of low-energy proton-induced SEUs by minimizing energy straggle

DOE PAGES

Dodds, Nathaniel Anson; Dodd, Paul E.; Shaneyfelt, Marty R.; ...

2015-12-01

In this study, we present low-energy proton single-event upset (SEU) data on a 65 nm SOI SRAM whose substrate has been completely removed. Since the protons only had to penetrate a very thin buried oxide layer, these measurements were affected by far less energy loss, energy straggle, flux attrition, and angular scattering than previous datasets. The minimization of these common sources of experimental interference allows more direct interpretation of the data and deeper insight into SEU mechanisms. The results show a strong angular dependence, demonstrate that energy straggle, flux attrition, and angular scattering affect the measured SEU cross sections, andmore » prove that proton direct ionization is the dominant mechanism for low-energy proton-induced SEUs in these circuits.« less

When the Second Language Takes the Lead: Neurocognitive Processing Changes in the First Language of Adult Attriters.

PubMed

Kasparian, Kristina; Steinhauer, Karsten

2017-01-01

Although research on multilingualism has revealed continued neuroplasticity for language-learning beyond what was previously expected, it remains controversial whether and to what extent a second language (L2) acquired in adulthood may induce changes in the neurocognitive processing of a first language (L1). First language (L1) attrition in adulthood offers new insight on neuroplasticity and the factors that modulate neurocognitive responses to language. To date, investigations of the neurocognitive correlates of L1 attrition and of factors influencing these mechanisms are still scarce. Moreover, most event-related-potential (ERP) studies of second language processing have focused on L1 influence on the L2, while cross-linguistic influence in the reverse direction has been underexplored. Using ERPs, we examined the real-time processing of Italian relative-clauses in 24 Italian-English adult migrants with predominant use of English since immigration and reporting attrition of their native-Italian (Attriters), compared to 30 non-attriting monolinguals in Italy (Controls). Our results showed that Attriters differed from Controls in their acceptability judgment ratings and ERP responses when relative clause constructions were ungrammatical in English, though grammatical in Italian. Controls' ERP responses to unpreferred sentence constructions were consistent with garden path effects typically observed in the literature for these complex sentences. In contrast, due to L2-English influence, Attriters were less sensitive to semantic cues than to word-order preferences, and processed permissible Italian sentences as outright morphosyntactic violations. Key factors modulating processing differences within Attriters were the degree of maintained L1 exposure, length of residence in the L2 environment and L2 proficiency - with higher levels of L2 immersion and proficiency associated with increased L2 influence on the L1. To our knowledge, this is the first demonstration that high levels of L2 proficiency and exposure may render a grammatical sentence in one's native language ungrammatical. These group differences strongly point to distinct processing strategies and provide evidence that even a "stabilized" L1 grammar is subject to change after a prolonged period of L2 immersion and reduced L1 use, especially in linguistic areas promoting cross-linguistic influence.

The effect of surface nanocrystallization on plasma nitriding behaviour of AISI 4140 steel

NASA Astrophysics Data System (ADS)

Li, Yang; Wang, Liang; Zhang, Dandan; Shen, Lie

2010-11-01

A plastic deformation surface layer with nanocrystalline grains was produced on AISI 4140 steel by means of surface mechanical attrition treatment (SMAT). Plasma nitriding of SMAT and un-SMAT AISI 4140 steel was carried out by a low-frequency pulse excited plasma unit. A series of nitriding experiments has been conducted at temperatures ranging from 380 to 500 °C for 8 h in an NH 3 gas. The samples were characterized using X-ray diffraction, scanning electron microscopy, optical microscopy and Vickers microhardness tester. The results showed that a much thicker compound layer with higher hardness was obtained for the SMAT samples when compared with un-SMAT samples after nitriding at the low temperature. In particular, plasma nitriding SMAT AISI 4140 steel at 380 °C for 8 h can produced a compound layer of 2.5 μm thickness with very high hardness on the surface, which is similar to un-SMAT samples were plasma nitrided at approximately 430 °C within the same time.

Enhanced bonding property of cold-sprayed Zn-Al coating on interstitial-free steel substrate with a nanostructured surface layer

NASA Astrophysics Data System (ADS)

Liang, Y. L.; Wang, Z. B.; Zhang, J.; Zhang, J. B.; Lu, K.

2016-11-01

By means of surface mechanical attrition treatment (SMAT), a gradient nanostructured surface layer was fabricated on a hot-rolled interstitial-free steel plate. A Zn-Al coating was subsequently deposited on the SMAT sample by using cold spray process. The bonding property of the coating on the SMAT substrate was compared with that on the coarse-grained (CG) sample. Stud-pull tests showed that the bonding strength in the as-sprayed SMAT sample is ∼30% higher than that in the as-sprayed CG sample. No further improvement in bonding strength was achieved in the coated SMAT sample after annealing at 400 °C, mostly due to the formation of cracks and intermetallic compounds at the coating/substrate interface in an earlier stage (<30 min) and in a final stage (>90 min), respectively. The enhanced bonding property of the Zn-Al coating on the SMAT sample might be related with the promoted atomic diffusion and hardness in the nanostructured surface layer.

An Evaluation of a Borided Layer Formed on Ti-6Al-4V Alloy by Means of SMAT and Low-Temperature Boriding

PubMed Central

Yao, Quantong; Sun, Jian; Fu, Yuzhu; Tong, Weiping; Zhang, Hui

2016-01-01

In this paper, a nanocrystalline surface layer without impurities was fabricated on Ti-6Al-4V alloy by means of surface mechanical attrition treatment (SMAT). The grain size in the nanocrystalline layer is about 10 nm and grain morphology displays a random crystallographic orientation distribution. Subsequently, the low-temperature boriding behaviors (at 600 °C) of the SMAT sample, including the phase composition, microstructure, micro-hardness, and brittleness, were investigated in comparison with those of coarse-grained sample borided at 1100 °C. The results showed that the boriding kinetics could be significantly enhanced by SMAT, resulting in the formation of a nano-structured boride layers on Ti-6Al-4V alloy at lower temperature. Compared to the coarse-grained boriding sample, the SMAT boriding sample exhibits a similar hardness value, but improved surface toughness. The satisfactory surface toughness may be attributed to the boriding treatment that was carried out at lower temperature. PMID:28774115

Unraveling Deformation Mechanisms in Gradient Structured Metals

NASA Astrophysics Data System (ADS)

Moering, Jordan Alexander

Gradient structures have demonstrated high strength and high ductility, introducing new mechanisms to challenge conventional mechanics. This work develops a method for characterizing the shear strain in gradient structured steel and presents evidence of a texture gradient that develops in Surface Mechanical Attrition Treatment (SMAT). Mechanics underlying some theories of the strengthening mechanisms in gradient structured metals are introduced, followed by the fabrication and testing of gradient structured aluminum rod. The round geometry is intrinsically different from its flat counterparts, which leads to a multiaxial stress state evolving in tension. The aluminum exhibits strengthening beyond rule of mixtures, and texture evolution in the post-mortem sample indicates that out of plane stresses operate within the gradient. Finally, another gradient structured aluminum rod is shown to exhibit higher strength and higher elongation to failure in a variety of sample diameters and processing conditions. The GND density and microstructural evolution showed no significant changes during mechanical testing, and high resolution strain mapping was successfully completed within the core of the material. These discoveries and contributions to the field should help continue unraveling the deformation mechanisms of gradient structured metals.

A crowdsourced nickel-and-dime approach to analog OBM research: A behavioral economic framework for understanding workforce attrition.

PubMed

Henley, Amy J; DiGennaro Reed, Florence D; Reed, Derek D; Kaplan, Brent A

2016-09-01

Incentives are a popular method to achieve desired employee performance; however, research on optimal incentive magnitude is lacking. Behavioral economic demand curves model persistence of responding in the face of increasing cost and may be suitable to examine the reinforcing value of incentives on work performance. The present use-inspired basic study integrated an experiential human operant task within a crowdsourcing platform to evaluate the applicability of behavioral economics for quantifying changes in workforce attrition. Participants included 88 Amazon Mechanical Turk Workers who earned either a $0.05 or $0.10 incentive for completing a progressively increasing response requirement. Analyses revealed statistically significant differences in breakpoint between the two groups. Additionally, a novel translation of the Kaplan-Meier survival-curve analyses for use within a demand curve framework allowed for examination of elasticity of workforce attrition. Results indicate greater inelastic attrition in the $0.05 group. We discuss the benefits of a behavioral economic approach to modeling employee behavior, how the metrics obtained from the elasticity of workforce attrition analyses (e.g., P max ) may be used to set goals for employee behavior while balancing organizational costs, and how economy type may have influenced observed outcomes. © 2016 Society for the Experimental Analysis of Behavior.

Bend strengths of reaction bonded silicon nitride prepared from dry attrition milled silicon powder

NASA Technical Reports Server (NTRS)

Herbell, T. P.; Glasgow, T. K.

1979-01-01

Dry attrition milled silicon powder was compacted, sintered in helium, and reaction bonded in nitrogen-4 volume percent hydrogen. Bend strengths of bars with as-nitrided surfaces averaged as high as 210 MPa at room temperature and 220 MPa at 1400 C. Bars prepared from the milled powder were stronger than those prepared from as-received powder at both room temperature and at 1400 C. Room temperature strength decreased with increased milling time and 1400 C strength increased with increased milling time.

Dental Wear: Attrition, Erosion, and Abrasion-A Palaeo-Odontological Approach.

PubMed

Sperber, Geoffrey H

2017-06-17

This paper reviews the surface ablation of early hominin teeth by attrition, abrasion, and erosive dental wear. The occurrence of these lesions is explored in a sample of South African fossil australopithecine dentitions revealing excessive wear. Interpretation of the nature of the dietary components causing such wear in the absence of carious erosion provides insight into the ecology of the Plio-pleistocene epoch (1-2 million years ago). Fossil teeth inform much of the living past by their retained evidence after death. Tooth wear is the ultimate forensic dental evidence of lives lived.

Enhancing the mechanical and biological performance of a metallic biomaterial for orthopedic applications through changes in the surface oxide layer by nanocrystalline surface modification.

PubMed

Bahl, Sumit; Shreyas, P; Trishul, M A; Suwas, Satyam; Chatterjee, Kaushik

2015-05-07

Nanostructured metals are a promising class of biomaterials for application in orthopedics to improve the mechanical performance and biological response for increasing the life of biomedical implants. Surface mechanical attrition treatment (SMAT) is an efficient way of engineering nanocrystalline surfaces on metal substrates. In this work, 316L stainless steel (SS), a widely used orthopedic biomaterial, was subjected to SMAT to generate a nanocrystalline surface. Surface nanocrystallization modified the nature of the oxide layer present on the surface. It increased the corrosion-fatigue strength in saline by 50%. This increase in strength is attributed to a thicker oxide layer, residual compressive stresses, high strength of the surface layer, and lower propensity for intergranular corrosion in the nanocrystalline layer. Nanocrystallization also enhanced osteoblast attachment and proliferation. Intriguingly, wettability and surface roughness, the key parameters widely acknowledged for controlling the cellular response remained unchanged after nanocrystallization. The observed cellular behavior is explained in terms of the changes in electronic properties of the semiconducting passive oxide film present on the surface of 316L SS. Nanocrystallization increased the charge carrier density of the n-type oxide film likely preventing denaturation of the adsorbed cell-adhesive proteins such as fibronectin. In addition, a net positive charge developed on the otherwise neutral oxide layer, which is known to facilitate cellular adhesion. The role of changes in the electronic properties of the oxide films on metal substrates is thus highlighted in this work. This study demonstrates the advantages of nanocrystalline surface modification by SMAT for processing metallic biomaterials used in orthopedic implants.

Nanoscale wear as a stress-assisted chemical reaction

NASA Astrophysics Data System (ADS)

Jacobs, Tevis D. B.; Carpick, Robert W.

2013-02-01

Wear of sliding contacts leads to energy dissipation and device failure, resulting in massive economic and environmental costs. Typically, wear phenomena are described empirically, because physical and chemical interactions at sliding interfaces are not fully understood at any length scale. Fundamental insights from individual nanoscale contacts are crucial for understanding wear at larger length scales, and to enable reliable nanoscale devices, manufacturing and microscopy. Observable nanoscale wear mechanisms include fracture and plastic deformation, but recent experiments and models propose another mechanism: wear via atom-by-atom removal (`atomic attrition'), which can be modelled using stress-assisted chemical reaction kinetics. Experimental evidence for this has so far been inferential. Here, we quantitatively measure the wear of silicon--a material relevant to small-scale devices--using in situ transmission electron microscopy. We resolve worn volumes as small as 25 +/- 5 nm3, a factor of 103 lower than is achievable using alternative techniques. Wear of silicon against diamond is consistent with atomic attrition, and inconsistent with fracture or plastic deformation, as shown using direct imaging. The rate of atom removal depends exponentially on stress in the contact, as predicted by chemical rate kinetics. Measured activation parameters are consistent with an atom-by-atom process. These results, by direct observation, establish atomic attrition as the primary wear mechanism of silicon in vacuum at low loads.

Teacher Attrition: A Review of Literature.

ERIC Educational Resources Information Center

Macdonald, Douane

1999-01-01

Reviews contemporary international attrition research in order to examine: the definition of teacher attrition; patterns of attrition; influences upon attrition; the impact of attrition; and strategies used to decrease attrition. The paper concludes that research on teacher attrition requires the development of more comprehensive databases on…

Surface Area, and Oxidation Effects on Nitridation Kinetics of Silicon Powder Compacts

NASA Technical Reports Server (NTRS)

Bhatt, R. T.; Palczer, A. R.

1998-01-01

Commercially available silicon powders were wet-attrition-milled from 2 to 48 hr to achieve surface areas (SA's) ranging from 1.3 to 70 sq m/g. The surface area effects on the nitridation kinetics of silicon powder compacts were determined at 1250 or 1350 C for 4 hr. In addition, the influence of nitridation environment, and preoxidation on nitridation kinetics of a silicon powder of high surface area (approximately equals 63 sq m/g) was investigated. As the surface area increased, so did the percentage nitridation after 4 hr in N2 at 1250 or 1350 C. Silicon powders of high surface area (greater than 40 sq m/g) can be nitrided to greater than 70% at 1250 C in 4 hr. The nitridation kinetics of the high-surface-area powder compacts were significantly delayed by preoxidation treatment. Conversely, the nitridation environment had no significant influence on the nitridation kinetics of the same powder. Impurities present in the starting powder, and those accumulated during attrition milling, appeared to react with the silica layer on the surface of silicon particles to form a molten silicate layer, which provided a path for rapid diffusion of nitrogen and enhanced the nitridation kinetics of high surface area silicon powder.

Peroneus Brevis Attrition & Longitudinal Split Tear without Subluxation and Associated Hypertrophy of Peronal Tubercle" - Treatment of an Uncommon Lesion.

PubMed

Tiwari, Mukesh; Singh, Varun; Bhargava, Rakesh

2015-01-01

Peroneus brevis tendinitis with its attritional longitudinal split rupture without any subluxation from peroneal groove and associated enlarged peroneal tubercle is un common presentation. A 40 year old female presented with moderate swelling and tenderness over the lateral and dorso-lateral aspect of left ankle with history of old trauma to ankle with swelling, persistant pain and difficulty in walking. On physical examination during passive eversion and inversion the excursion of the peroneal tendons was painful. Most tender point was just posterior to the tip of the fibula. During surgery we found the intact superior peroneal ligament with both peroneal tendons placed at normal site without subluxation, tendon sheath was inflamed and swollen, on further dissection we could see the attrition of inner surface of the peroneus brevis and a 2 cm longitudinal split tear of the same. Although rare but peroneus brevis tendon attrition and tear can occur without subluxation from peronal groove. Refractory ankle pain on lateral aspect presenting with on and off swelling should arise suspicion of peroneal tendon tear. Correct diagnosis and proper surgical repair can produce excellent results.

Dental Wear: Attrition, Erosion, and Abrasion—A Palaeo-Odontological Approach

PubMed Central

Sperber, Geoffrey H.

2017-01-01

This paper reviews the surface ablation of early hominin teeth by attrition, abrasion, and erosive dental wear. The occurrence of these lesions is explored in a sample of South African fossil australopithecine dentitions revealing excessive wear. Interpretation of the nature of the dietary components causing such wear in the absence of carious erosion provides insight into the ecology of the Plio-pleistocene epoch (1–2 million years ago). Fossil teeth inform much of the living past by their retained evidence after death. Tooth wear is the ultimate forensic dental evidence of lives lived. PMID:29563425

Particle size reduction of Si3N4 with Si3N4 milling hardware

NASA Technical Reports Server (NTRS)

Herbell, T. P.; Freedman, M. R.; Kiser, J. D.

1986-01-01

The grinding of Si3N4 powder using reaction bonded Si3N4 attrition, vibratory, and ball mills with Si3N4 media was examined. The rate of particle size reduction and the change in the chemical composition of the powder were determined in order to compare the grinding efficiency and the increase in impurity content resulting from mill and media wear for each technique. Attrition and vibratory milling exhibited rates of specific surface area increase that were approximately eight times that observed in ball milling. Vibratory milling introduced the greatest impurity pickup.

When the Second Language Takes the Lead: Neurocognitive Processing Changes in the First Language of Adult Attriters

PubMed Central

Kasparian, Kristina; Steinhauer, Karsten

2017-01-01

Although research on multilingualism has revealed continued neuroplasticity for language-learning beyond what was previously expected, it remains controversial whether and to what extent a second language (L2) acquired in adulthood may induce changes in the neurocognitive processing of a first language (L1). First language (L1) attrition in adulthood offers new insight on neuroplasticity and the factors that modulate neurocognitive responses to language. To date, investigations of the neurocognitive correlates of L1 attrition and of factors influencing these mechanisms are still scarce. Moreover, most event-related-potential (ERP) studies of second language processing have focused on L1 influence on the L2, while cross-linguistic influence in the reverse direction has been underexplored. Using ERPs, we examined the real-time processing of Italian relative-clauses in 24 Italian-English adult migrants with predominant use of English since immigration and reporting attrition of their native-Italian (Attriters), compared to 30 non-attriting monolinguals in Italy (Controls). Our results showed that Attriters differed from Controls in their acceptability judgment ratings and ERP responses when relative clause constructions were ungrammatical in English, though grammatical in Italian. Controls’ ERP responses to unpreferred sentence constructions were consistent with garden path effects typically observed in the literature for these complex sentences. In contrast, due to L2-English influence, Attriters were less sensitive to semantic cues than to word-order preferences, and processed permissible Italian sentences as outright morphosyntactic violations. Key factors modulating processing differences within Attriters were the degree of maintained L1 exposure, length of residence in the L2 environment and L2 proficiency – with higher levels of L2 immersion and proficiency associated with increased L2 influence on the L1. To our knowledge, this is the first demonstration that high levels of L2 proficiency and exposure may render a grammatical sentence in one’s native language ungrammatical. These group differences strongly point to distinct processing strategies and provide evidence that even a “stabilized” L1 grammar is subject to change after a prolonged period of L2 immersion and reduced L1 use, especially in linguistic areas promoting cross-linguistic influence. PMID:28424634

The role of oxidation in the fretting wear process

NASA Technical Reports Server (NTRS)

Bill, R. C.

1980-01-01

Fretting experiments were conducted on titanium, a series of Ni-Cr-Al alloys and on some high temperature turbine alloys at room temperature and at elevated temperatures in air and in various inert environments. It was found that, depending on temperature and environment, the fretting behavior of the materials examined could be classified according to four general types of behavior. Briefly, these types of behavior were: (1) the complete absence of oxidation, as in inert environments, generally leading to low rates of fretting wear but high fretting friction; (2) gradual attrition of surface oxide with each fretting stroke, found in these experiments to operate in concert with other dominating mechanisms; (3) rapid oxidation at surface fatigue damage sites, resulting in undermining and rapid disintegration of the load bearing surface; and (4) the formation of coherent, protective oxide film, resulting in low rates of fretting wear. An analytical model predicting conditions favorable to the fourth type of behavior was outlined.

Synthesis of nanoparticles from malleable and ductile metals using powder-free, reactant-assisted mechanical attrition.

PubMed

McMahon, Brandon W; Perez, Jesus Paulo L; Yu, Jiang; Boatz, Jerry A; Anderson, Scott L

2014-11-26

A reactant-assisted mechanochemical method was used to produce copious nanoparticles from malleable/ductile metals, demonstrated here for aluminum, iron, and copper. The milling media is intentionally degraded via a reactant-accelerated wear process, where the reactant aids particle production by binding to the metal surfaces, enhancing particle production, and reducing the tendency toward mechanochemical (cold) welding. The mechanism is explored by comparing the effects of different types of solvents and solvent mixtures on the amount and type of particles produced. Particles were functionalized with oleic acid to aid in particle size separation, enhance dispersion in hydrocarbon solvents, and protect the particles from oxidation. For aluminum and iron, the result is air-stable particles, but for copper, the suspended particles are found to dissolve when exposed to air. Characterization was performed using electron microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, solid state nuclear magnetic resonance, and X-ray photoelectron spectroscopy. Density functional theory was used to examine the nature of carboxylic acid binding to the aluminum surface, confirming the dominance of bridging bidentate binding.

The generation and morphology of single-crystal silicon carbide wear particles under adhesive conditions

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1981-01-01

Sliding friction experiments were performed in vacuum at room temperature on a plane-type SiC surface in contact with iron-based binary alloys. Multiangular and spherical wear particles were found to form as a result of multipass sliding. The multiangular particles were produced by primary and secondary cracking of the 0001, 10(-)10, and 11(-)20 plane-type cleavage planes under the Hertzian stress field or local inelastic deformation zone. When alloy surfaces are in contact with silicon carbide under a load of 0.2 N, the alloy around the contact area is subjected to stresses that are close to the elastic limit in the elastic deformation region and/or exceed it. It was also found that spherical wear particles may be produced by two mechanisms: a penny-shaped fracture along the circular stress trajectories under the local inelastic deformation zone, and the attrition and fatigue of wear particles.

The development of biomarkers to reduce attrition rate in drug discovery focused on oncology and central nervous system.

PubMed

Safavi, Maliheh; Sabourian, Reyhaneh; Abdollahi, Mohammad

2016-10-01

The task of discovery and development of novel therapeutic agents remains an expensive, uncertain, time-consuming, competitive, and inefficient enterprise. Due to a steady increase in the cost and time of drug development and the considerable amount of resources required, a predictive tool is needed for assessing the safety and efficacy of a new chemical entity. This study is focused on the high attrition rate in discovery and development of oncology and central nervous system (CNS) medicines, because the failure rate of these medicines is higher than others. Some approaches valuable in reducing attrition rates are proposed and the judicious use of biomarkers is discussed. Unlike the significant progress made in identifying and characterizing novel mechanisms of disease processes and targeted therapies, the process of novel drug development is associated with an unacceptably high attrition rate. The application of clinically qualified predictive biomarkers holds great promise for further development of therapeutic targets, improved survival, and ultimately personalized medicine sets for patients. Decisions such as candidate selection, development risks, dose ranging, early proof of concept/principle, and patient stratification are based on the measurements of biologically and/or clinically validated biomarkers.

Effect of ball milling materials and methods on powder processing of Bi2223 superconductors

NASA Astrophysics Data System (ADS)

Yavuz, M.; Maeda, H.; Vance, L.; Liu, H. K.; Dou, S. X.

1998-10-01

Various milling systems consisting of agate and polypropylene grinding containers, agate and YSZ balls, and dry and wet milling were used in planetary ball-milling and YSZ balls and YSZ container were used in wet and dry attrition milling. The differently milled powders were then evaluated by measurements of particle size, surface area, porosity, size distribution and chemical analysis of the Si, Zr and C contents. The results show that dry milling is much more efficient for particle size reduction in planetary milling than wet milling, whereas wet milling and dry milling gave quite similar results in attrition milling. Meanwhile 0953-2048/11/10/056/img6 contamination was found in powder milled with an agate container with agate balls. Some C contamination from the polypropylene container was detected after milling, but negligible Zr from YSZ balls and C from the grinding carrier (hexane). It was found that after 1 h milling in the planetary mill fracture mechanisms transform from the elastic to the plastic region. Therefore, further milling is not very effective. It was also shown that the Bi2212 phase decomposes into several non-superconducting oxides such as 0953-2048/11/10/056/img7, CuO and a main amorphous phase after extensive dry milling.

Superior Tensile Ductility in Bulk Metallic Glass with Gradient Amorphous Structure

PubMed Central

Wang, Q.; Yang, Y.; Jiang, H.; Liu, C. T.; Ruan, H. H.; Lu, J.

2014-01-01

Over centuries, structural glasses have been deemed as a strong yet inherently ‘brittle’ material due to their lack of tensile ductility. However, here we report bulk metallic glasses exhibiting both a high strength of ~2 GPa and an unprecedented tensile elongation of 2–4% at room temperature. Our experiments have demonstrated that intense structural evolution can be triggered in theses glasses by the carefully controlled surface mechanical attrition treatment, leading to the formation of gradient amorphous microstructures across the sample thickness. As a result, the engineered amorphous microstructures effectively promote multiple shear banding while delay cavitation in the bulk metallic glass, thus resulting in superior tensile ductility. The outcome of our research uncovers an unusual work-hardening mechanism in monolithic bulk metallic glasses and demonstrates a promising yet low-cost strategy suitable for producing large-sized, ultra-strong and stretchable structural glasses. PMID:24755683

Particle-size reduction of Si3N4 powder with Si3N4 milling hardware

NASA Technical Reports Server (NTRS)

Herbell, T. P.; Freedman, M. R.; Kiser, J. D.

1986-01-01

The grinding of Si3N4 powder using reaction bonded Si3N4 attrition, vibratory, and ball mills with Si3N4 media was examined. The rate of particle size reduction and the change in the chemical composition of the powder were determined in order to compare the grinding efficiency and the increase in impurity content resulting from mill and media wear for each technique. Attrition and vibratory milling exhibited rates of specific surface area increase that were approximately eight times that observed in ball milling. Vibratory milling introduced the greatest impurity pickup.

Attrition in Smoking Cessation Intervention Studies: A Systematic Review.

PubMed

Belita, Emily; Sidani, Souraya

2015-12-01

Withdrawal of participants from intervention studies has dire methodological and clinical consequences. Attrition rates in smoking cessation studies have been found to be particularly high. Identifying factors that contribute to attrition may inform strategies to address the problem and prevent its consequences. This systematic review had 2 objectives: to report attrition rates, and to identify factors that influence attrition of adult smokers participating in smoking cessation intervention studies. Inclusion criteria were (1) published between 1980 and 2015; (2) experimental or quasi-experimental design; (3) pharmacological, educational, or behavioural intervention; (4) target population of adult smokers; (5) examination of attrition rate; and (6) exploration of factors associated with attrition and/or of reasons given by participants for withdrawing. These criteria were met by 10 studies. Attrition rates ranged from 10.8% to 77%. A small number of demographic, clinical, behavioural, health, health-related beliefs, and logistical factors were related to attrition. The report of high attrition rates underlines the importance of incorporating strategies to minimize attrition in smoking cessation studies. Strategies to reduce attrition are proposed. Copyright© by Ingram School of Nursing, McGill University.

A rapid review of the rate of attrition from the health workforce.

PubMed

Castro Lopes, Sofia; Guerra-Arias, Maria; Buchan, James; Pozo-Martin, Francisco; Nove, Andrea

2017-03-01

Attrition or losses from the health workforce exacerbate critical shortages of health workers and can be a barrier to countries reaching their universal health coverage and equity goals. Despite the importance of accurate estimates of the attrition rate (and in particular the voluntary attrition rate) to conduct effective workforce planning, there is a dearth of an agreed definition, information and studies on this topic. We conducted a rapid review of studies published since 2005 on attrition rates of health workers from the workforce in different regions and settings; 1782 studies were identified, of which 51 were included in the study. In addition, we analysed data from the State of the World's Midwifery (SoWMy) 2014 survey and associated regional survey for the Arab states on the annual voluntary attrition rate for sexual, reproductive, maternal and newborn health workers (mainly midwives, doctors and nurses) in the 79 participating countries. There is a diversity of definitions of attrition and barely any studies distinguish between total and voluntary attrition (i.e. choosing to leave the workforce). Attrition rate estimates were provided for different periods of time, ranging from 3 months to 12 years, using different calculations and data collection systems. Overall, the total annual attrition rate varied between 3 and 44% while the voluntary annual attrition rate varied between 0.3 to 28%. In the SoWMy analysis, 49 countries provided some data on voluntary attrition rates of their SRMNH cadres. The average annual voluntary attrition rate was 6.8% across all cadres. Attrition, and particularly voluntary attrition, is under-recorded and understudied. The lack of internationally comparable definitions and guidelines for measuring attrition from the health workforce makes it very difficult for countries to identify the main causes of attrition and to develop and test strategies for reducing it. Standardized definitions and methods of measuring attrition are required.

Novel Attrition-Resistant Fischer Tropsch Catalyst

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weast, Logan, E.; Staats, William, R.

2009-05-01

There is a strong national interest in the Fischer-Tropsch synthesis process because it offers the possibility of making liquid hydrocarbon fuels from reformed natural gas or coal and biomass gasification products. This project explored a new approach that had been developed to produce active, attrition-resistant Fischer-Tropsch catalysts that are based on glass-ceramic materials and technology. This novel approach represented a promising solution to the problem of reducing or eliminating catalyst attrition and maximizing catalytic activity, thus reducing costs. The technical objective of the Phase I work was to demonstrate that glass-ceramic based catalytic materials for Fischer-Tropsch synthesis have resistance tomore » catalytic deactivation and reduction of particle size superior to traditional supported Fischer-Tropsch catalyst materials. Additionally, these novel glass-ceramic-based materials were expected to exhibit catalytic activity similar to the traditional materials. If successfully developed, the attrition-resistant Fischer-Tropsch catalyst materials would be expected to result in significant technical, economic, and social benefits for both producers and public consumers of Fischer-Tropsch products such as liquid fuels from coal or biomass gasification. This program demonstrated the anticipated high attrition resistance of the glass-ceramic materials. However, the observed catalytic activity of the materials was not sufficient to justify further development at this time. Additional testing documented that a lack of pore volume in the glass-ceramic materials limited the amount of surface area available for catalysis and consequently limited catalytic activity. However, previous work on glass-ceramic catalysts to promote other reactions demonstrated that commercial levels of activity can be achieved, at least for those reactions. Therefore, we recommend that glass-ceramic materials be considered again as potential Fischer-Tropsch catalysts if it can be demonstrated that materials with adequate pore volume can be produced. During the attrition resistance tests, it was learned that the glass-ceramic materials are very abrasive. Attention should be paid in any further developmental efforts to the potential for these hard, abrasive materials to damage reactors.« less

Factors related to attrition from VA healthcare use: findings from the National Survey of Women Veterans.

PubMed

Hamilton, Alison B; Frayne, Susan M; Cordasco, Kristina M; Washington, Donna L

2013-07-01

While prior research characterizes women Veterans' barriers to accessing and using Veterans Health Administration (VA) care, there has been little attention to women who access VA and use services, but then discontinue use. Recent data suggest that among women Veterans, there is a 30 % attrition rate within 3 years of initial VA use. To compare individual characteristics and perceptions about VA care between women Veteran VA attriters (those who discontinue use) and non-attriters (those who continue use), and to compare recent versus remote attriters. Cross-sectional, population-based 2008-2009 national telephone survey. Six hundred twenty-six attriters and 2,065 non-attriters who responded to the National Survey of Women Veterans. Population weighted demographic, military and health characteristics; perceptions about VA healthcare; length of time since last VA use; among attriters, reasons for no longer using VA care. Fifty-four percent of the weighted VA ever user population reported that they no longer use VA. Forty-five percent of attrition was within the past ten years. Attriters had better overall health (p = 0.007), higher income (p < 0.001), and were more likely to have health insurance (p < 0.001) compared with non-attriters. Attriters had less positive perceptions of VA than non-attriters, with attriters having lower ratings of VA quality and of gender-specific features of VA care (p < 0.001). Women Veterans who discontinued VA use since 2001 did not differ from those with more remote VA use on most measures of VA perceptions. Overall, among attriters, distance to VA sites of care and having alternate insurance coverage were the most common reasons for discontinuing VA use. We found high VA attrition despite recent advances in VA care for women Veterans. Women's attrition from VA could reduce the critical mass of women Veterans in VA and affect current system-wide efforts to provide high-quality care for women Veterans. An understanding of reasons for attrition can inform organizational efforts to re-engage women who have attrited, to retain current users, and potentially to attract new VA patients.

Particulate Formation from a Copper Oxide-Based Oxygen ...

EPA Pesticide Factsheets

Attrition behavior and particle loss of a copper oxide-based oxygen carrier from a methane chemical looping combustion (CLC) process was investigated in a fluidized bed reactor. The aerodynamic diameters of most elutriated particulates, after passing through a horizontal settling duct, range between 2 and 5 μm. A notable number of submicron particulates are also identified. Oxygen carrier attrition was observed to lead to increased CuO loss resulting from the chemical looping reactions, i.e., Cu is enriched in small particles generated primarily from fragmentation in the size range of 10-75 μm. Cyclic reduction and oxidation reactions in CLC have been determined to weaken the oxygen carrier particles, resulting in increased particulate emission rates when compared to oxygen carriers without redox reactions. The generation rate for particulates < 10 μm was found to decrease with progressive cycles over as-prepared oxygen carrier particles and then reach a steady state. The surface of the oxygen carrier is also found to be coarsened due to a Kirkendall effect, which also explains the enrichment of Cu on particle surfaces and in small particles. As a result, it is important to collect and reprocess small particles generated from chemical looping processes to reduce oxygen carrier loss. The redox reactions associated with chemical looping combustion play an important role in particle attrition in the fluidized bed. Reaction-induced local stresses, due to the r

Principals' Perceptions of Teacher Attrition in Indiana Catholic Schools, Checking for Agreement with Ingersoll's Theoretical Framework on Teacher Attrition in Private Schools

ERIC Educational Resources Information Center

Brettnacher, Joseph A.

2012-01-01

Problem. Some Catholic schools report high teacher attrition rates. Understanding reasons for teacher attrition and responding to those issues is one of the many responsibilities of principals. However, it is unclear what Catholic principals understand about teacher attrition. Ingersoll's extensive research on teacher attrition has provided a…

Sociodemographic and psychiatric determinants of attrition in the Netherlands Study of Depression and Anxiety (NESDA).

PubMed

Lamers, Femke; Hoogendoorn, Adriaan W; Smit, Johannes H; van Dyck, Richard; Zitman, Frans G; Nolen, Willem A; Penninx, Brenda W

2012-01-01

Although attrition is inevitable in longitudinal epidemiological studies, psychiatric studies are thought to be especially sensitive to attrition. This study aimed to evaluate the sociodemographic and psychiatric determinants of attrition at 2-year follow-up in the Netherlands Study of Depression and Anxiety. Logistic regression was used to examine sociodemographic and psychiatric determinants of attrition and the influence of clinical psychiatric characteristics on attrition. In addition, differences in determinants between 3 types of attrition (refusal, noncontact, and not able to participate) were evaluated. The attrition rate at the 2-year follow-up assessment was 12.9% (385/2981), representing 6 deceased persons, 250 refusers, 51 noncontacts, and 78 persons unable to participate because of health reasons. Determinants of attrition were younger age, less years of education, not being of North European descent, being recruited in Amsterdam, no previous participation in research, and having major depressive disorder. Only the effects of age, sampling site, and previous participation in research differed between types of attrition. Furthermore, comorbid depressive and anxiety disorders and higher symptom severity were associated with attrition. In contrast to the view that psychiatric epidemiological research is more prone to high attrition rates, this study revealed a relatively low attrition rate. Furthermore, both sociodemographic and psychiatric variables were independent determinants of attrition. Oversampling of subgroups that are at higher risk of dropout may be advisable for future psychiatric cohort studies. Copyright © 2012 Elsevier Inc. All rights reserved.

Terahertz acoustic phonon detection from a compact surface layer of spherical nanoparticles powder mixture of aluminum, alumina and multi-walled carbon nanotube

NASA Astrophysics Data System (ADS)

Abouelsayed, A.; Ebrahim, M. R.; El hotaby, W.; Hassan, S. A.; Al-Ashkar, Emad

2017-10-01

We present terahertz spectroscopy study on spherical nanoparticles powder mixture of aluminum, alumina, and MWCNTs induced by surface mechanical attrition treatment (SMAT) of aluminum substrates. Surface alloying of AL, Al2O3 0.95% and MWCNTs 0.05% powder mixture was produced during SMAT process, where a compact surface layer of about 200 μm due to ball bombardment was produced from the mixture. Al2O3 alumina powder played a significant role in MWCNTs distribution on surface, those were held in deformation surface cites of micro-cavities due to SMAT process of Al. The benefits are the effects on resulted optical properties of the surface studied at the terahertz frequency range due to electrical isolation confinement effects and electronic resonance disturbances exerted on Al electronic resonance at the same range of frequencies. THz acoustic phonon around 0.53-0.6 THz (17-20 cm-1) were observed at ambient conditions for the spherical nanoparticles powder mixture of Al, Al2O3 and MWCNTs. These results suggested that the presence of Al2O3 and MWCNTs during SMAT process leads to the optically detection of such acoustic phonon in the THz frequency range.

Attrition in Models of Intergenerational Links Using the PSID with Extensions to Health and to Sibling Models*

PubMed Central

Fitzgerald, John M.

2012-01-01

Selective attrition potentially biases estimation of intergenerational links in health and economic status. This paper documents attrition in the PSID through 2007 for a cohort of children, and investigates attrition bias in intergenerational models predicting adult health, education and earnings, including models based on sibling differences. Although attrition affects unconditional means, the weighted PSID generally maintains its representativeness along key dimensions in comparison to the National Health Interview Survey. Using PSID, sibling correlations in outcomes and father-son correlations in earnings are not significantly affected by attrition. Models of intergenerational links with covariates yield more mixed results with females showing few robust impacts of attrition and males showing potential attrition bias for education and earnings outcomes. For adult health outcomes conditional on child background, neither gender shows significant impacts of attrition for the age ranges and models considered here. Sibling models do not produce robustly higher attrition impacts than individual models. PMID:22368743

Microstructural characterization of Ti-6Al-4V alloy subjected to the duplex SMAT/plasma nitriding.

PubMed

Pi, Y; Faure, J; Agoda-Tandjawa, G; Andreazza, C; Potiron, S; Levesque, A; Demangel, C; Retraint, D; Benhayoune, H

2013-09-01

In this study, microstructural characterization of Ti-6Al-4V alloy, subjected to the duplex surface mechanical attrition treatment (SMAT)/nitriding treatment, leading to improve its mechanical properties, was carried out through novel and original samples preparation methods. Instead of acid etching which is limited for morphological characterization by scanning electron microscopy (SEM), an original ion polishing method was developed. Moreover, for structural characterization by transmission electron microscopy (TEM), an ion milling method based with the use of two ions guns was also carried out for cross-section preparation. To demonstrate the efficiency of the two developed methods, morphological investigations were done by traditional SEM and field emission gun SEM. This was followed by structural investigations through selected area electron diffraction (SAED) coupled with TEM and X-ray diffraction techniques. The results demonstrated that ionic polishing allowed to reveal a variation of the microstructure according to the surface treatment that could not be observed by acid etching preparation. TEM associated to SAED and X-ray diffraction provided information regarding the nanostructure compositional changes induced by the duplex SMAT/nitriding process. Copyright © 2013 Wiley Periodicals, Inc.

Impact of missing data mechanism on the estimate of change: a case study on cognitive function and polypharmacy among older persons

PubMed Central

Lavikainen, Piia; Leskinen, Esko; Hartikainen, Sirpa; Möttönen, Jyrki; Sulkava, Raimo; Korhonen, Maarit J

2015-01-01

Longitudinal studies typically suffer from incompleteness of data. Attrition is a major problem in studies of older persons since participants may die during the study or are too frail to participate in follow-up examinations. Attrition is typically related to an individual’s health; therefore, ignoring it may lead to too optimistic inferences, for example, about cognitive decline or changes in polypharmacy. The objective of this study is to compare the estimates of level and slope of change in 1) cognitive function and 2) number of drugs in use between the assumptions of ignorable and non-ignorable missingness. This study demonstrates the usefulness of latent variable modeling framework. The results suggest that when the missing data mechanism is not known, it is preferable to conduct analyses both under ignorable and non-ignorable missing data assumptions. PMID:25678815

Impact of missing data mechanism on the estimate of change: a case study on cognitive function and polypharmacy among older persons.

PubMed

Lavikainen, Piia; Leskinen, Esko; Hartikainen, Sirpa; Möttönen, Jyrki; Sulkava, Raimo; Korhonen, Maarit J

2015-01-01

Longitudinal studies typically suffer from incompleteness of data. Attrition is a major problem in studies of older persons since participants may die during the study or are too frail to participate in follow-up examinations. Attrition is typically related to an individual's health; therefore, ignoring it may lead to too optimistic inferences, for example, about cognitive decline or changes in polypharmacy. The objective of this study is to compare the estimates of level and slope of change in 1) cognitive function and 2) number of drugs in use between the assumptions of ignorable and non-ignorable missingness. This study demonstrates the usefulness of latent variable modeling framework. The results suggest that when the missing data mechanism is not known, it is preferable to conduct analyses both under ignorable and non-ignorable missing data assumptions.

Attrition Cost Model Instruction Manual

ERIC Educational Resources Information Center

Yanagiura, Takeshi

2012-01-01

This instruction manual explains in detail how to use the Attrition Cost Model program, which estimates the cost of student attrition for a state's higher education system. Programmed with SAS, this model allows users to instantly calculate the cost of attrition and the cumulative attrition rate that is based on the most recent retention and…

Attrition in Navy Recruit Training: An Analysis from the First Watch on the First Term of Enlistment

DTIC Science & Technology

2008-08-01

employed full-time and/or were a full-time student before joining the Navy. Results show that there were significant differences in attrition rates...RTC attrition rates almost as high as those reporting being unemployed (8.4%). Also unexpected, fill-time students had an attrition rate of 7.9...Respondents who reported that they were both full time students and worked full- time before joining the Navy had an attrition rate of 7.5%. This attrition

Language Attrition: The Fate of the Start.

ERIC Educational Resources Information Center

Hansen, Lynne

2001-01-01

Reviews the literature on psycholinguistic aspects of language attrition over the past half decade. Discusses evidence from studies on hesitation phenomena in attriter speech, variables affecting language attrition, and relearning. (Author/VWL)

A meta-analysis investigating factors underlying attrition rates in infant ERP studies.

PubMed

Stets, Manuela; Stahl, Daniel; Reid, Vincent M

2012-01-01

In this meta-analysis, we examined interrelationships between characteristics of infant event-related potential (ERP) studies and their attrition rates. One-hundred and forty-nine published studies provided information on 314 experimental groups of which 181 provided data on attrition. A random effects meta-analysis revealed a high average attrition rate of 49.2%. Additionally, we used meta-regression for 178 groups with attrition data to analyze which variables best explained attrition variance. Our main findings were that the nature of the stimuli-visual, auditory, or combined as well as if stimuli were animated-influenced exclusion rates from the final analysis and that infant age did not alter attrition rates.

Analysis of Early Military Attrition Behavior.

DTIC Science & Technology

1984-06-01

military separation. Although hizh school graduation status is the primary single factor affecting attrition, age and previous employment stability...assignment like individual suitability and satisfaction do not significantly influence early attrition; the early attrition rate of nonhigh- school ...a recruit with a single previous employer. I I V IS BLANK vi * Various indicators of military job match had no significant impact on early attrition

First Language Attrition: An Investigation of Taiwanese Tones and Tone Sandhi

ERIC Educational Resources Information Center

Chang, Yufen

2012-01-01

First language (L1) attrition research focuses on syntactic and morphological deterioration in environments where L1 "attriters" rarely have contact with their L1, such as immigrants. There is no study that investigates L1 attrition in tones and in contexts where L1 can still be often heard. This study examines this attrition type in…

PREPARATION OF HIGH-DENSITY THORIUM OXIDE SPHERES

DOEpatents

McNees, R.A. Jr.; Taylor, A.J.

1963-12-31

A method of preparing high-density thorium oxide spheres for use in pellet beds in nuclear reactors is presented. Sinterable thorium oxide is first converted to free-flowing granules by means such as compression into a compact and comminution of the compact. The granules are then compressed into cubes having a density of 5.0 to 5.3 grams per cubic centimeter. The cubes are tumbled to form spheres by attrition, and the spheres are then fired at 1250 to 1350 deg C. The fired spheres are then polished and fired at a temperature above 1650 deg C to obtain high density. Spherical pellets produced by this method are highly resistant to mechanical attrition hy water. (AEC)

Association of Time to Attrition in Surgical Residency With Individual Resident and Programmatic Factors.

PubMed

Yeo, Heather L; Abelson, Jonathan S; Symer, Matthew M; Mao, Jialin; Michelassi, Fabrizio; Bell, Richard; Sedrakyan, Art; Sosa, Julie A

2018-02-21

Attrition in general surgery residency remains high, and attrition that occurs in the later years is the most worrisome. Although several studies have retrospectively investigated the timing of attrition, no study to date has prospectively evaluated a national cohort of residents to understand which residents are at risk for attrition and at what point during residency. To prospectively evaluate individual resident and programmatic factors associated with the timing of attrition during general surgery residency. This longitudinal, national cohort study administered a survey to all categorical general surgery interns from the class of 2007-2008 during their first 30 days of residency and linked the data with 9-year follow-up data assessing program completion. Data were collected from June 1, 2007, through June 30, 2016. Kaplan-Meier curves evaluating time to attrition during the 9 years after the start of residency. Among our sample of 836 residents (306 women [36.6%] and 528 men [63.2%]; gender unknown in 2), cumulative survival analysis demonstrated overall attrition for the cohort of 20.8% (n = 164). Attrition was highest in the first postgraduate year (67.6% [n = 111]; absolute rate, 13.3%) but continued during the next 6 years, albeit at a lower rate. Beginning in the first year, survival analysis demonstrated higher attrition among Hispanic compared with non-Hispanic residents (21.1% vs 12.4%; P = .04) and at military programs compared with academic or community programs after year 1 (32.3% vs 11.0% or 13.5%; P = .01). Beginning in year 4 of residency, higher attrition was encountered among women compared with men (23.3% vs 17.4%; P = .05); at year 5, at large compared with small programs (26.0% vs 18.4%; P = .04). Race and program location were not associated with attrition. Although attrition was highest during the internship year, late attrition persists, particularly among women and among residents in large programs. These results provide a framework for timing of interventions in graduate surgical training that target residents most at risk for late attrition.

Is Heavy Drinking Really Associated With Attrition From College? The Alcohol–Attrition Paradox

PubMed Central

Martinez, Julia A.; Sher, Kenneth J.; Wood, Phillip K.

2009-01-01

Student attrition at colleges across the United States poses a significant problem for students and families, higher educational institutions, and the nation's workforce competing in the global economy. Heavy drinking is a highly plausible contributor to the problem. However, there is little evidence that it is a reliable predictor of attrition. Notably, few studies take into account indicators of collegiate engagement that are associated with both heavy drinking and persistence in college. Event-history analysis was used to estimate the effect of heavy drinking on attrition among 3,290 undergraduates at a large midwestern university during a 4-year period, and student attendance at a number of college events was included as covariates. Results showed that heavy drinking did not predict attrition bivariately or after controlling for precollege predictors of academic success. However, after controlling for event attendance (an important indicator of collegiate engagement), heavy drinking was found to predict attrition. These findings underscore the importance of the college context in showing that heavy drinking does in fact predict attrition and in considering future intervention efforts to decrease attrition and also heavy drinking. PMID:18778140

[Case of occlusal reconstruction for severe attrition].

PubMed

Ueda, Takayuki

2006-01-01

A 57-year-old female complained of aesthetic disturbance, dysmasesis and phonation disorder by attrition. She had severe attrition of almost teeth. To avoid metal color exposure and attrition of opposing teeth, hybrid ceramics were used for veneered crowns and fixed partial denture. Since the prosthetic treatment, the patient wears a night guard to prevent attrition of her teeth and prosthesis. There has been no specific trouble during the 4-year follow-up. It is considered that using hybrid ceramics for veneering crowns and fixed partial denture and night guard help to prevent the attrition of opposing teeth and abrasion of prosthesis.

An experimental demonstration that early-life competitive disadvantage accelerates telomere loss

PubMed Central

Nettle, Daniel; Monaghan, Pat; Gillespie, Robert; Brilot, Ben; Bedford, Thomas; Bateson, Melissa

2015-01-01

Adverse experiences in early life can exert powerful delayed effects on adult survival and health. Telomere attrition is a potentially important mechanism in such effects. One source of early-life adversity is the stress caused by competitive disadvantage. Although previous avian experiments suggest that competitive disadvantage may accelerate telomere attrition, they do not clearly isolate the effects of competitive disadvantage from other sources of variation. Here, we present data from an experiment in European starlings (Sturnus vulgaris) that used cross-fostering to expose siblings to divergent early experience. Birds were assigned either to competitive advantage (being larger than their brood competitors) or competitive disadvantage (being smaller than their brood competitors) between days 3 and 12 post-hatching. Disadvantage did not affect weight gain, but it increased telomere attrition, leading to shorter telomere length in disadvantaged birds by day 12. There were no effects of disadvantage on oxidative damage as measured by plasma lipid peroxidation. We thus found strong evidence that early-life competitive disadvantage can accelerate telomere loss. This could lead to faster age-related deterioration and poorer health in later life. PMID:25411450

An experimental demonstration that early-life competitive disadvantage accelerates telomere loss.

PubMed

Nettle, Daniel; Monaghan, Pat; Gillespie, Robert; Brilot, Ben; Bedford, Thomas; Bateson, Melissa

2015-01-07

Adverse experiences in early life can exert powerful delayed effects on adult survival and health. Telomere attrition is a potentially important mechanism in such effects. One source of early-life adversity is the stress caused by competitive disadvantage. Although previous avian experiments suggest that competitive disadvantage may accelerate telomere attrition, they do not clearly isolate the effects of competitive disadvantage from other sources of variation. Here, we present data from an experiment in European starlings (Sturnus vulgaris) that used cross-fostering to expose siblings to divergent early experience. Birds were assigned either to competitive advantage (being larger than their brood competitors) or competitive disadvantage (being smaller than their brood competitors) between days 3 and 12 post-hatching. Disadvantage did not affect weight gain, but it increased telomere attrition, leading to shorter telomere length in disadvantaged birds by day 12. There were no effects of disadvantage on oxidative damage as measured by plasma lipid peroxidation. We thus found strong evidence that early-life competitive disadvantage can accelerate telomere loss. This could lead to faster age-related deterioration and poorer health in later life.

The 9th Grade Shock and the High School Dropout Crisis

PubMed Central

Pharris-Ciurej, Nikolas; Hirschman, Charles; Willhoft, Joseph

2011-01-01

Retrospective questions on educational attainment in national surveys and censuses tend to over-estimate high school graduation rates by 15 to 20 percentage points relative to administrative records. Administrative data on educational enrollment are, however, only available at the aggregate level (state, school district, and school levels) and the recording of inter-school transfers are generally incomplete. With access to linked individual-level administrative records from a very large “West Coast metropolitan school district” we track patterns of high school attrition and on-time high school graduation of individual students. Even with adjustments for the omission of out-of-district transfers (estimates of omission are presented), the results of this study show that failure in high school, as indexed by retention and attrition, are almost as common as on-time high school graduation. In addition to the usual risk factors of disadvantaged background, we find that the “9th grade shock”—an unpredicted decline in academic performance upon entering high school—is a key mechanism behind the continuing crisis of high school attrition. PMID:23017804

The 9th grade shock and the high school dropout crisis.

PubMed

Pharris-Ciurej, Nikolas; Hirschman, Charles; Willhoft, Joseph

2012-05-01

Retrospective questions on educational attainment in national surveys and censuses tend to over-estimate high school graduation rates by 15-20% points relative to administrative records. Administrative data on educational enrollment are, however, only available at the aggregate level (state, school district, and school levels) and the recording of inter-school transfers are generally incomplete. With access to linked individual-level administrative records from a very large "West Coast metropolitan school district" we track patterns of high school attrition and on-time high school graduation of individual students. Even with adjustments for the omission of out-of-district transfers (estimates of omission are presented), the results of this study show that failure in high school, as indexed by retention and attrition, are almost as common as on-time high school graduation. In addition to the usual risk factors of disadvantaged background, we find that the "9th grade shock"-an unpredicted decline in academic performance upon entering high school-is a key mechanism behind the continuing crisis of high school attrition. Copyright © 2011 Elsevier Inc. All rights reserved.

Association of General Surgery Resident Remediation and Program Director Attitudes With Resident Attrition.

PubMed

Schwed, Alexander C; Lee, Steven L; Salcedo, Edgardo S; Reeves, Mark E; Inaba, Kenji; Sidwell, Richard A; Amersi, Farin; Are, Chandrakanth; Arnell, Tracey D; Damewood, Richard B; Dent, Daniel L; Donahue, Timothy; Gauvin, Jeffrey; Hartranft, Thomas; Jacobsen, Garth R; Jarman, Benjamin T; Melcher, Marc L; Mellinger, John D; Morris, Jon B; Nehler, Mark; Smith, Brian R; Wolfe, Mary; Kaji, Amy H; de Virgilio, Christian

2017-12-01

Previous studies of resident attrition have variably included preliminary residents and likely overestimated categorical resident attrition. Whether program director attitudes affect attrition has been unclear. To determine whether program director attitudes are associated with resident attrition and to measure the categorical resident attrition rate. This multicenter study surveyed 21 US program directors in general surgery about their opinions regarding resident education and attrition. Data on total resident complement, demographic information, and annual attrition were collected from the program directors for the study period of July 1, 2010, to June 30, 2015. The general surgery programs were chosen on the basis of their geographic location, previous collaboration with some coauthors, prior work in surgical education and research, or a program director willing to participate. Only categorical surgical residents were included in the study; thus, program directors were specifically instructed to exclude any preliminary residents in their responses. Five-year attrition rates (2010-2011 to 2014-2015 academic years) as well as first-time pass rates on the General Surgery Qualifying Examination and General Surgery Certifying Examination of the American Board of Surgery (ABS) were collected. High- and low-attrition programs were compared. The 21 programs represented different geographic locations and 12 university-based, 3 university-affiliated, and 6 independent program types. Programs had a median (interquartile range [IQR]) number of 30 (20-48) categorical residents, and few of those residents were women (median [IQR], 12 [5-17]). Overall, 85 of 966 residents (8.8%) left training during the study period: 15 (17.6%) left after postgraduate year 1, 34 (40.0%) after postgraduate year 2, and 36 (42.4%) after postgraduate year 3 or later. Forty-four residents (51.8%) left general surgery for another surgical discipline, 21 (24.7%) transferred to a different surgery program, and 18 (21.2%) exited graduate medical education altogether. Each program had an annual attrition rate ranging from 0.73% to 6.0% (median [IQR], 2.5% [1.5%-3.4%]). Low-attrition programs were more likely than high-attrition programs to use resident remediation (21.0% vs 6.8%; P < .001). Median (IQR) Qualifying Examination pass rates (93% [90%-98%] vs 92% [86%-100%]; P = .92) and Certifying Examination pass rates (83% [68%-84%] vs 81% [71%-86%]; P = .47) were similar. Program directors at high-attrition programs were more likely than their counterparts at low-attrition programs to agree with this statement: "I feel that it is my responsibility as a program director to redirect residents who should not be surgeons." The overall 5-year attrition rate of 8.8% was significantly lower than previously reported. Program directors at low-attrition programs were more likely to use resident remediation. Variations in attrition may be explained by program director attitudes, although larger studies are needed to further define program factors affecting attrition.

Attrition and retention in upper limb prosthetics research: experience of the VA home study of the DEKA arm.

PubMed

Resnik, Linda; Klinger, Shana

2017-11-01

(1) Describe study attrition; (2) identify reasons for attrition, and (3) discuss implications for prosthetic prescription and design of future device studies. Design and methodological procedures used: Completion phase (during in-laboratory training, after training, or home use) was identified for 42 participants. Qualitative data were analyzed to identify attrition reasons. Reasons were classified as related to the DEKA arm, or not. Study attrition was 57%, with 43% completing the full study. Attrition during the in-laboratory portion was 21%. Reasons for attrition were related to the DEKA arm entirely or in-part for 42%, 25%, respectively. Most common reasons were scheduling/personal (54%); device weight (29%); and dissatisfaction with device (25%). About 21% withdrew because of concerns about compliance with study protocol. This study had a high attrition rate with evidence of selective attrition due to device characteristics. Strategies to minimize attrition and the importance of tracking reasons for withdrawal are discussed. Given that retention could be an indicator of willingness to adopt the DEKA arm, findings suggest that it would be prudent to provide patients with the opportunity to train with the DEKA arm before a decision is made regarding the appropriateness of the device for the patient. Implications for Rehabilitation This study of a new upper limb prosthesis, the DEKA arm, had a 57% attrition rate with evidence of selective attrition due to characteristics of the DEKA arm. Findings point to the need for strategies to minimize attrition in future studies. Findings also illustrate the importance of tracking reasons for subject withdrawal in longitudinal prosthesis device studies. Because participant retention in longitudinal device studies may be an indicator of future willingness to adopt a device, our findings suggest that it would be prudent to provide patients with the opportunity to train with the DEKA arm before a final decision is made regarding the appropriateness of the device for the patient.

Predictors of treatment attrition as indicators for program improvement not offender shortcomings: a study of sex offender treatment attrition.

PubMed

Beyko, Michelle J; Wong, Stephen C P

2005-10-01

This study classified potential attrition predictors under the domains of risk, need and responsivity (D. Andrews & J. Bonta, 2003). Non-sexual criminogenic needs (e.g. aggression, rule violating behaviors) and responsivity factors (e.g. lack of motivation and denial) were the two main clusters of predictors that correctly classified 95.3% of program completers and non-completers using discriminant function analysis in a sample of high-risk male sexual offenders treated in an accredited inpatient sex offender treatment program. Rapists were more aggressive than other types of sex offenders and were more likely to drop out of treatment. Some studies of predictors of treatment attrition have used offender problem behaviors or psychopathologies to predict attrition and then use the information to exclude offenders from treatment. Others have argued, and we concur, that results of attrition research should not be used to develop an "attrition profile" to exclude offenders from treatment. Predictors of attrition should be seen as markers for program improvement, rather than shortcomings of the offender. Suggestions for program improvements to reduce the rate of attrition, based on results of research, are presented.

Relative risk of home hemodialysis attrition in patients using a telehealth platform.

PubMed

Weinhandl, Eric D; Collins, Allan J

2017-12-06

Home hemodialysis (HHD) facilitates increased treatment frequency, which may improve patient outcomes. However, attrition due to technique failure limits the clinical effectiveness of the modality. Nx2me Connected Health is a telehealth platform that enables ongoing assessment of HHD patients using NxStage equipment, and that may reduce patient burden. We aimed to assess whether use of Nx2me was associated with risk of HHD attrition. We compared risks of all-cause attrition, dialysis cessation (i.e., death or transplant), and technique failure in Nx2me users and matched control patients, using a retrospective cohort study. We also compared the likelihood of HHD training graduation in patients who initiated use of Nx2me during training with the likelihood in matched control patients. Matching factors included date of HHD initiation, NxStage treatment duration at initiation of follow-up, and prescribed treatment frequency. We used stratified Fine-Gray and Cox regression to compare risks, with adjustment for demographic factors and vascular access modality, and stratification by matched cluster. We identified 606 Nx2me users; 49.5% initiated use of Nx2me in <3 months after initiation of HHD with NxStage equipment. Adjusted hazard ratios (AHRs) of all-cause attrition, dialysis cessation, and technique failure were 0.80 (95% confidence interval, 0.68-0.95), 1.10 (0.86-1.41), and 0.71 (0.57-0.87), respectively, for Nx2me users vs. matched controls. AHRs were similar in patients who initiated use of Nx2me in <3 months after initiation of HHD. The AHR of HHD training graduation was 1.61 (1.10-2.36) in patients who initiated use of Nx2me within 2 weeks of training initiation vs. matched controls. Use of Nx2me was associated with lower risk of all-cause attrition, lower risk of technique failure, and higher likelihood of HHD training graduation. Further studies are needed to identify the mechanisms by which use of a telehealth platform may improve clinical outcomes and reduce patient burden. © 2017 The Authors Hemodialysis International published by Wiley Periodicals, Inc. on behalf of International Society for Hemodialysis.

Changing Patterns of Nonprior Service Attrition in the Army National Guard and Army Reserve

DTIC Science & Technology

1988-07-01

attrition risk is gender . Women are at much higher risk of attrition than males with similar characteristics. However, the gap between male and... gender (Table 5.1). Women are at much higher risk of attrition than similar males. However, the gap between male and female attrition narrows...the basis of gender , educational achievement, aptitude scores, race, and age. 1Vi" The characteristic that makes the largest consistent difference in

Dental attrition and associated factors in adolescents 14 to 19 years of age: a pilot study.

PubMed

Casanova-Rosado, Juan F; Medina-Solís, Carlo E; Vallejos-Sánchez, Ana A; Casanova-Rosado, Alejandro J; Maupomé, Gerardo; Avila-Burgos, Leticia

2005-01-01

This cross-sectional study evaluated the relationship between attrition and diverse variables in 390 Mexican adolescents aged 14 to 19 years. An ordinal scoring system was used to describe the severity of attrition. Attrition prevalence was 33.3% and was associated with older age, presence of defective restorations, Class II malocclusion, and perception of stress level. Our results suggest that attrition is present in 1 of every 3 adolescents.

Effects of high CD4 cell counts on death and attrition among HIV patients receiving antiretroviral treatment: an observational cohort study.

PubMed

Tang, Zhenzhu; Pan, Stephen W; Ruan, Yuhua; Liu, Xuanhua; Su, Jinming; Zhu, Qiuying; Shen, Zhiyong; Zhang, Heng; Chen, Yi; Lan, Guanghua; Xing, Hui; Liao, Lingjie; Feng, Yi; Shao, Yiming

2017-06-09

Current WHO guidelines recommend initiating ART regardless of CD4+ cell count. In response, we conducted an observational cohort study to assess the effects of pre-ART CD4+ cell count levels on death, attrition, and death or attrition in HIV treated patients. This large HIV treatment cohort study (n = 49,155) from 2010 to 2015 was conducted in Guangxi, China. We used a Cox regression model to analyze associations between pre-ART CD4+ cell counts and death, attrition, and death or attrition. The average mortality and ART attrition rates among all treated patients were 2.63 deaths and 5.32 attritions per 100 person-years, respectively. Compared to HIV patients with <350 CD4+ cells/mm 3 at ART initiation, HIV patients with >500 CD4+ cells/mm 3 at ART initiation had a significantly lower mortality rate (Adjusted hazard ratio: 0.56, 95% CI: 0.40-0.79), but significantly higher ART attrition rate (AHR: 1.17, 95% CI: 1.03-1.33). Results from this study suggest that HIV patients with high CD4+ cell counts at the time of ART initiation may be at greater risk of treatment attrition. To further reduce ART attrition, it is imperative that patient education and healthcare provider training on ART adherence be enhanced and account for CD4 levels at ART initiation.

An experiment on the attrition of acid demineralized dentine in vitro.

PubMed

Li, H; Liu, M C; Deng, M; Moazzez, R; Bartlett, D W

2011-03-01

A laboratory investigation was designed to test the hypothesis that acids increase the rate of wear caused by attrition on dentine. Dentine sections from 10 teeth were polished, cleaned in an ultrasonic bath and divided into 8 equally sized areas. The occlusal tip of a tooth, placed vertically in a wear machine and loaded at 150 N, was moved against each dentine section for 5000 return strokes with artificial saliva acting as a lubricant. Each dentine section was divided into 8 sections and half randomly immersed in a 1% citric acid solution (pH 2.3) for 20 minutes. The wear regime produced 8 wear scars in total per dentine sample. The volume of each wear scar was measured using a contacting digitizing profilometer. A total of 80 wear scars were produced with 40 treated with acid and 40 acting as controls. The mean for wear volume of the dentine scars with acid was 4.84 μm(3) (1.38) and for the non-acid surface 2.95 μm(3) (0.86). This difference was statistically significant (p < 0.05). These results support the hypothesis that acids increase the rate of wear caused by attrition on dentine. © 2011 Australian Dental Association.

Teacher Attrition and Retention: A Meta-Analytic and Narrative Review of the Research

ERIC Educational Resources Information Center

Borman, Geoffrey D.; Dowling, N. Maritza

2008-01-01

This comprehensive meta-analysis on teacher career trajectories, consisting of 34 studies of 63 attrition moderators, seeks to understand why teaching attrition occurs, or what factors moderate attrition outcomes. Personal characteristics of teachers are important predictors of turnover. Attributes of teachers' schools, including organizational…

Reducing Nursing Student Attrition: The Search for Effective Strategies

ERIC Educational Resources Information Center

Kubec, Cathy

2017-01-01

This review of the literature summarizes recent exploration of nursing student attrition. Attrition places financial burdens on students who leave a program, results in lost revenue for the college, and compounds the existing nursing shortage. Some research investigated the student selection process, which seeks to decrease attrition by admitting…

Benchmarking Attrition: What Can We Learn From Other Industries?

ERIC Educational Resources Information Center

Delta Cost Project at American Institutes for Research, 2012

2012-01-01

This brief summarizes Internet-based research into other industries that may offer useful analogies for thinking about student attrition in higher education, in particular for setting realistic benchmarks for reductions in attrition. Reducing attrition to zero or close to zero is not a realistic possibility in higher education. Students are…

Telomere Attrition in Isolated High-Grade Prostatic Intraepithelial Neoplasia and Surrounding Stroma Is Predictive of Prostate Cancer1

PubMed Central

Joshua, Anthony Michael; Vukovic, Bisera; Braudey, Ilan; Hussein, Sundus; Zielenska, Maria; Srigley, John; Evans, Andrew; Squire, Jeremy Andrew

2007-01-01

Abstract The causes of early genomic events underlying the development of prostate cancer (CaP) remain unclear. The onset of chromosomal instability is likely to facilitate the formation of crucial genomic aberrations both in the precursor lesion high-grade prostatic intraepithelial neoplasia (HPIN) and in CaP. Instability generated by telomere attrition is one potential mechanism that could initiate chromosomal rearrangements. In this study, normalized telomere length variation was examined in a cohort of 68 men without CaP who had HPIN only on prostatic biopsies. Multiple significant associations between telomere attrition and eventual diagnosis of CaP in the HPIN and in the surrounding stroma were found. Kaplan-Meier analysis of telomere length demonstrated a significantly increased risk for the development of cancer with short telomeres in the surrounding stroma [P = .035; hazard ratio (HR) = 2.12; 95% confidence interval (95% CI) = 0.231–0.956], and a trend for HPIN itself (P = .126; HR = 1.72; 95% CI = 0.287–1.168). Cox regression analysis also demonstrated significance between the time from the original biopsy to the diagnosis of cancer and telomere length in HPIN and in the surrounding stroma. These analyses showed significance, both alone and in combination with baseline prostate-specific antigen, and lend support to the hypothesis that telomere attrition in prostatic preneoplasia may be fundamental to the generation of chromosomal instability and to the emergence of CaP. PMID:17325746

Gender Issues Related to Graduate Student Attrition in Two Science Departments.

ERIC Educational Resources Information Center

Ferreira, Maria M.

2003-01-01

Explores gender issues that contributed to the differential attrition rate of men and women graduate students in two science departments (biology and chemistry) at a large research university. Analysis indicated a significantly larger student attrition rate in chemistry than in biology. In each department the attrition rate for women was…

A Qualitative Study on the Effects of Teacher Attrition

ERIC Educational Resources Information Center

Wushishi, Aminu Aliyu; Fooi, Foo Say; Basri, Ramli; Baki, Roslen

2014-01-01

In this study the researchers explored the effects of teacher attrition in Niger state, Nigeria. The study examined how attrition is affecting the educational development of the state from the teachers' perspective. A qualitative method was used with the aim of extracting the inner feelings of the participants regarding the effects of attrition.…

Reducing Bias Due to Systematic Attrition in Longitudinal Studies: The Benefits of Multiple Imputation

ERIC Educational Resources Information Center

Asendorpf, Jens B.; van de Schoot, Rens; Denissen, Jaap J. A.; Hutteman, Roos

2014-01-01

Most longitudinal studies are plagued by drop-out related to variables at earlier assessments (systematic attrition). Although systematic attrition is often analysed in longitudinal studies, surprisingly few researchers attempt to reduce biases due to systematic attrition, even though this is possible and nowadays technically easy. This is…

Exploring Beginning Teachers' Attrition in the Netherlands

ERIC Educational Resources Information Center

den Brok, Perry; Wubbels, Theo; van Tartwijk, Jan

2017-01-01

Based on a review of recent studies and reports, this research investigates attrition among beginning teachers in the Netherlands as well as reasons for teacher attrition, and compares the finding with studies on this topic conducted elsewhere in the world. The findings suggest that attrition among beginning teachers in the Netherlands with a…

Attrition bias in rheumatoid arthritis databanks: a case study of 6346 patients in 11 databanks and 65,649 administrations of the Health Assessment Questionnaire.

PubMed

Krishnan, Eswar; Murtagh, Kirsten; Bruce, Bonnie; Cline, Denise; Singh, Gurkirpal; Fries, James F

2004-07-01

Patient dropout (attrition) can bias and threaten validity of databank-based studies. Although there are several databanks of rheumatoid arthritis (RA) in operation, this phenomenon has not been well studied. We studied the attrition patterns of patients with RA in 11 long-running databanks where patients were followed using semiannual Health Assessment Questionnaires. Attrition rates were calculated as the proportion of living patients who were in active followup at the cutoff date. Mantel-Haenszel methods and Weibull regression were used to model the relationship between attrition and age, sex, race, education, disease duration, functional disability, and other characteristics. Overall, 6346 patients with RA were recruited into the study cohorts and followed for 32,823 person-years with 65,649 observations. The crude attrition rate was 3.8% per cycle. Rates were lowest in community-based databanks. Smaller size of the centers, inner-city location, and university clinic settings were associated with worse attrition. In multivariable analyses, younger age, lower levels of education, and non-Caucasian race predicted attrition. Level of disability and disease duration were not associated with attrition. Conclusion. In terms of person-years of followup and observation-points, this may be the largest study on attrition to date. While it is possible to have very high overall retention rates, certain types of databanks (smaller, inner-city-based, and university-based) are more likely to be biased due to selective retention of older, more educated Caucasian patients.

Dental attrition models predicting temporomandibular joint disease or masticatory muscle pain versus asymptomatic controls.

PubMed

Seligman, D A; Pullinger, A G

2006-11-01

To determine whether patients with temporomandibular joint disease or masticatory muscle pain can be usefully differentiated from asymptomatic controls using multifactorial classification tree models of attrition severity and/or rates. Measures of attrition severity and rates in patients diagnosed with disc displacement (n = 52), osteoarthrosis (n = 74), or masticatory muscle pain only (n = 43) were compared against those in asymptomatic controls (n = 132). Cross-validated classification tree models were tested for fit with sensitivity, specificity, accuracy and log likelihood accountability. The model for identifying asymptomatic controls only required the three measures of attrition severity (anterior, mediotrusive and laterotrusive posterior) to be differentiated from the patients with a 74.2 +/- 3.8% cross-validation accuracy. This compared with cross-validation accuracies of 69.7 +/- 3.7% for differentiating disc displacement using anterior and laterotrusive attrition severity, 68.7 +/- 3.9% for differentiating disc displacement using anterior and laterotrusive attrition rates, 70.9 +/- 3.3% for differentiating osteoarthrosis using anterior attrition severity and rates, 94.6 +/- 2.1% for differentiating myofascial pain using mediotrusive and laterotrusive attrition severity, and 92.0 +/- 2.1% for differentiating myofascial pain using mediotrusive and anterior attrition rates. The myofascial pain models exceeded the > or =75% sensitivity and > or =90% specificity thresholds recommended for diagnostic tests, and the asymptomatic control model approached these thresholds. Multifactorial models using attrition severity and rates may differentiate masticatory muscle pain patients from asymptomatic controls, and have some predictive value for differentiating intracapsular temporomandibular disorder patients as well.

Investigation of Sintering Temperature on Attrition Resistance of Highly Porous Diatomite Based Material

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garderen, Noemie van; Clemens, Frank J.; Scharf, Dagobert

2010-05-30

Highly porous diatomite based granulates with a diameter of 500 mum have been produced by an extrusion method. In order to investigate the relation between microstructure, phase composition and attrition resistance of the final product, the granulates were sintered between 800 and 1300 deg. C. Mean pore size of the granulates was evaluated by Hg-porosimetry. An increase of the pore size is observed in the range of 3.6 nm to 40 mum with increasing sintering temperature. Higher mean pore radii of 1.6 mum and 5.7 mum obtained by sintering at 800 and 1300 deg. C respectively. X-ray diffraction shows thatmore » mullite phase appears at 1100 deg. C due to the presence of clay. At 1100 deg. C diatomite (amorphous silicate) started to transform into alpha-cristobalite. Attrition resistance was determined by evaluating the amount of ground material passed through a sieve with a predefined mesh size. It was observed that a material sintered at high temperature leads to an increase of attrition resistance due to the decrease of total porosities and phase transformation. Due to the reason that attrition resistance significantly increased by sintering the granulates at higher temperature, a so called attrition resistance index was determined in order to compare all the different attrition resistance values. This attrition resistance index was determined by using the exponential component of the equation obtained from attrition resistance curves. It permits comparison of the attrition behaviour without a time influence.« less

Attrition analysed in five waves of a longitudinal yearly survey of smokers: findings from the ITC Netherlands survey.

PubMed

Zethof, Dennis; Nagelhout, Gera E; de Rooij, Mark; Driezen, Pete; Fong, Geoffrey T; van den Putte, Bas; Hummel, Karin; de Vries, Hein; Thompson, Mary E; Willemsen, Marc C

2016-08-01

Attrition bias can affect the external validity of findings. This article analyses attrition bias and assesses the effectiveness of replenishment samples on demographic and smoking-related characteristics for the International Tobacco Control Netherlands Survey, a longitudinal survey among smokers. Attrition analyses were conducted for the first five survey waves (2008-12). We assessed, including and excluding replenishment samples, whether the demographic composition of the samples changed between the first and fifth waves. Replenishment samples were tailored to ensure the sample remained representative of the smoking population. We also constructed a multivariable survival model of attrition that included all five waves with replenishment samples. Of the original 1820 respondents recruited in 2008, 46% participated again in 2012. Demographic differences between waves due to attrition were generally small and replenishment samples tended to minimize them further. The multivariable survival analysis revealed that only two of the 10 variables analysed were significant predictors of attrition: a weak effect for gender (men dropped out more often) and weak to moderate effects for age (respondents aged 15-24 years dropped out more than aged 25-39 years, who dropped out more than those aged 40+ years). Weak to moderate attrition effects were found for men and younger age groups. This information could be used to minimize respondent attrition. Our findings suggest that sampling weights and tailored replenishment samples can effectively compensate for attrition effects. This is already being done for the International Tobacco Control Netherlands Survey, including the categories that significantly predicted attrition in this study. © The Author 2016. Published by Oxford University Press on behalf of the European Public Health Association. All rights reserved.

A Study on Prevalence of Dental Attrition and its Relation to Factors of Age, Gender and to the Signs of TMJ Dysfunction.

PubMed

Yadav, Sangeeta

2011-06-01

A study was planned to determine the severity of dental attrition in adults of both sexes in different age groups and its possible relationship to temporomandibular disorders. 500 subjects comprising of 260 females and 240 males in the age group of 18-55 years were clinically examined for bruxism, attrition, and signs of temporomandibular disorders. Tooth sensitivity, tooth or restoration fracture, scalloping of tongue, ridging of buccal mucosa, TMJ sounds, muscle tenderness, TMJ tenderness, referred pain, pain on mouth opening and limitation of mouth opening were recorded along with attrition score in a proforma. The basic data was then analysed to arrive at certain conclusions. A high prevalence of attrition (88.0%) with increase in age (P < 0.00) and was seen more in males as compared to females (P < 0.01). On comparing attrition with some of the signs of bruxism it was shown that tooth or restoration fracture and scalloping of tongue had no relation to the severity of attrition score. Whereas a significant relation was seen between attrition and tooth sensitivity (P < 0.00), and ridging of buccal mucosa (P < 0.05). Muscle tenderness (P < 0.00), pain on mouth opening (P < 0.05) and deviation of mandible on mouth opening (P < 0.00) had significant relation to attrition. Other signs of temporomandibular disorders such as joint tenderness, referred pain, joint sounds and limitation of mouth opening had no relation to attrition score. This study showed a limited association between the severity of attrition and TMJ dysfunction.

Early Career Teacher Attrition in Australia: Inconvenient Truths about New Public Management

ERIC Educational Resources Information Center

Gallant, Andrea; Riley, Philip

2017-01-01

Early career teacher (ECT) attrition data are often challenged by those outside of the profession. Attrition rates can only be interpolated from existing data, but fall somewhere between 8 and 53%. The Australian workforce data on ECT attrition are problematized at the outset, before presenting a collective case study examining early career male…

Team-Based Learning Reduces Attrition in a First-Semester General Chemistry Course

ERIC Educational Resources Information Center

Comeford, Lorrie

2016-01-01

Team-based learning (TBL) is an instructional method that has been shown to reduce attrition and increase student learning in a number of disciplines. TBL was implemented in a first-semester general chemistry course, and its effect on attrition was assessed. Attrition from sections before implementing TBL (fall 2008 to fall 2009) was compared with…

Literature Review on Induction and Mentoring Related to Early Career Teacher Attrition and Retention

ERIC Educational Resources Information Center

Long, Julie S.; McKenzie-Robblee, Sue; Schaefer, Lee; Steeves, Pam; Wnuk, Sheri; Pinnegar, Eliza; Clandinin, D. Jean

2012-01-01

Early career teacher attrition is a matter of economic, social, and educational concern in many countries. Usually induction programs, including mentoring, are seen to alleviate the problem of early career teacher attrition. Mentoring/induction programs as a solution to what is defined as the problem of early career teacher attrition and retention…

Impact of participant attrition on child injury outcome estimates: a longitudinal birth cohort study in Australia

PubMed Central

Cameron, Cate M; Osborne, Jodie M; Spinks, Anneliese B; Davey, Tamzyn M; Sipe, Neil; McClure, Roderick J

2017-01-01

Background Longitudinal research is subject to participant attrition. Systemic differences between retained participants and those lost to attrition potentially bias prevalence of outcomes, as well as exposure-outcome associations. This study examines the impact of attrition on the prevalence of child injury outcomes and the association between sociodemographic factors and child injury. Methods Participants were recruited as part of the Environments for Healthy Living (EFHL) birth cohort study. Baseline data were drawn from maternal surveys. Child injury outcome data were extracted from hospital records, 2006–2013. Participant attrition status was assessed up to 2014. Rates of injury-related episodes of care were calculated, taking into account exposure time and Poisson regression was performed to estimate exposure-outcome associations. Results Of the 2222 participating families, 799 families (36.0%) had complete follow-up data. Those with incomplete data included 137 (6.2%) who withdrew, 308 (13.8%) were lost to follow-up and 978 families (44.0%) who were partial/non-responders. Families of lower socioeconomic status were less likely to have complete follow-up data (p<0.05). Systematic differences in attrition did not result in differential child injury outcomes or significant differences between the attrition and non-attrition groups in risk factor effect estimates. Participants who withdrew were the only group to demonstrate differences in child injury outcomes. Conclusion This research suggests that even with considerable attrition, if the proportion of participants who withdraw is minimal, overall attrition is unlikely to affect the population prevalence estimate of child injury or measures of association between sociodemographic factors and child injury. PMID:28667218

Analysis of dental attrition and mortality in the Medieval village of Tirup, Denmark.

PubMed

Boldsen, Jesper L

2005-02-01

New directions and new questions raised in the study of health in the past justify this reanalysis of the pattern of dental attrition in the Medieval Danish population of Tirup. Dental attrition was scored on all permanent molars from the Tirup skeletal sample. Scores were analyzed by means of logistic regression of the probability of having entered a given stage of wear for a given tooth in a way that is very similar to transition analysis. The primary determinant of dental attrition was age at death. In addition to age, the effects of sex, side, and dating were analyzed. In order to assess the homogeneity of the process of wearing teeth down, a third-order polynomial in age-at-death was also fitted to the transition probabilities. It was found that age is the single most important determinant of dental attrition, and that sex or side did not differentiate the rate of attrition. In several transitions, there was evidence of heterogeneity, indicating both random and systematic interpersonal differences in the rate of attrition and an association between the rate of attrition and age-at-death. It was found that attrition proceeded more quickly after AD 1300 than prior to that date. It is suggested that this was due to a possible general deterioration of living conditions in Northern Europe and an increased reliance on grain for food during the first half of the 14th century. The temporal effect on attrition rate accounts for some but not all the observed heterogeneity wear. 2004 Wiley-Liss, Inc.

Travel time and attrition from VHA care among women veterans: how far is too far?

PubMed

Friedman, Sarah A; Frayne, Susan M; Berg, Eric; Hamilton, Alison B; Washington, Donna L; Saechao, Fay; Maisel, Natalya C; Lin, Julia Y; Hoggatt, Katherine J; Phibbs, Ciaran S

2015-04-01

Travel time, an access barrier, may contribute to attrition of women veterans from Veterans Health Administration (VHA) care. We examined whether travel time influences attrition: (a) among women veterans overall, (b) among new versus established patients, and (c) among rural versus urban patients. This retrospective cohort study used logistic regression to estimate the association between drive time and attrition, overall and for new/established and rural/urban patients. In total, 266,301 women veteran VHA outpatients in the Fiscal year 2009. An "attriter" did not return for VHA care during the second through third years after her first 2009 visit (T0). Drive time (log minutes) was between the patient's residence and her regular source of VHA care. "New" patients had no VHA visits within 3 years before T0. Models included age, service-connected disability, health status, and utilization as covariates. Overall, longer drive times were associated with higher odds of attrition: drive time adjusted odds ratio=1.11 (99% confidence interval, 1.09-1.14). The relationship between drive time and attrition was stronger among new patients but was not modified by rurality. Attrition among women veterans is sensitive to longer drive time. Linking new patients to VHA services designed to reduce distance barriers (telemedicine, community-based clinics, mobile clinics) may reduce attrition among women new to VHA.

Understanding attrition from international Internet health interventions: a step towards global eHealth.

PubMed

Geraghty, Adam W A; Torres, Leandro D; Leykin, Yan; Pérez-Stable, Eliseo J; Muñoz, Ricardo F

2013-09-01

Worldwide automated Internet health interventions have the potential to greatly reduce health disparities. High attrition from automated Internet interventions is ubiquitous, and presents a challenge in the evaluation of their effectiveness. Our objective was to evaluate variables hypothesized to be related to attrition, by modeling predictors of attrition in a secondary data analysis of two cohorts of an international, dual language (English and Spanish) Internet smoking cessation intervention. The two cohorts were identical except for the approach to follow-up (FU): one cohort employed only fully automated FU (n = 16 430), while the other cohort also used 'live' contact conditional upon initial non-response (n = 1000). Attrition rates were 48.1 and 10.8% for the automated FU and live FU cohorts, respectively. Significant attrition predictors in the automated FU cohort included higher levels of nicotine dependency, lower education, lower quitting confidence and receiving more contact emails. Participants' younger age was the sole predictor of attrition in the live FU cohort. While research on large-scale deployment of Internet interventions is at an early stage, this study demonstrates that differences in attrition from trials on this scale are (i) systematic and predictable and (ii) can largely be eliminated by live FU efforts. In fully automated trials, targeting the predictors we identify may reduce attrition, a necessary precursor to effective behavioral Internet interventions that can be accessed globally.

Development of an attrition risk prediction tool.

PubMed

Fowler, John; Norrie, Peter

To review lecturers' and students' perceptions of the factors that may lead to attrition from pre-registration nursing and midwifery programmes and to identify ways to reduce the impact of such factors on the student's experience. Comparable attrition rates for nursing and midwifery students across various universities are difficult to monitor accurately; however, estimates that there is approximately a 25% national attrition rate are not uncommon. The financial and human implications of this are significant and worthy of investigation. A study was carried out in one medium-sized UK school of nursing and midwifery, aimed at identifying perceived factors associated with attrition and retention. Thirty-five lecturers were interviewed individually; 605 students completed a questionnaire, and of these, 10 were individually interviewed. Attrition data kept by the student service department were reviewed. Data were collected over an 18-month period in 2007-2008. Regression analysis of the student data identified eight significant predictors. Four of these were 'positive' factors in that they aided student retention and four were 'negative' in that they were associated with students' thoughts of resigning. Student attrition and retention is multifactorial, and, as such, needs to be managed holistically. One aspect of this management could be an attrition risk prediction tool.

[Study of dental attrition in a medieval adult population from Southwest France].

PubMed

Esclassan, R; Boimond, L; Sevin, A; Donat, R; Lucas, S; Grimoud, A M

2009-02-01

The aim of the authors was to study dental attrition in a medieval sample of paired mandibles and maxillas from the Southwest France (IX to XV century). We selected 58 adult individuals with maxillas and mandibles in good state of conservation, 29 women and 29 men from the medieval collection of Vilarnau-d'Amont (Western Pyrenees, France). Attrition was graded according to the Brabant index. We found a high prevalence of attrition in this sample. The first molars (M1) were the maxillary and mandibular teeth most concerned by attrition. The most frequent attrition level was level 2, with dentin exposure. We did not find any significant difference of tooth wear between maxillary and mandibular teeth, even if maxillary teeth seemed to be more worn. There was symmetry of attrition between the left and right side. There was no significant difference between men and women. Working on paired mandibles and maxillas showed that attrition in the middle age was a global phenomenon, intermaxillary and symmetric. It was much more severe than today, rapidly evolving and generalized because of the abrasive quality of food, cooking, chewing habits, and intensity of chewing pressure.

Parent binge eating and depressive symptoms as predictors of attrition in a family-based treatment for pediatric obesity.

PubMed

Braden, Abby L; Madowitz, Jennifer; Matheson, Brittany E; Bergmann, Kristie; Crow, Scott J; Boutelle, Kerri N

2015-04-01

Attrition is a significant problem in family-based treatment (FBT) for childhood obesity. Despite this, very few studies have examined factors associated with attrition. The current study examined parent symptoms of depression and binge eating as predictors of attrition in FBT. Participants included 77 parents of overweight children enrolled in FBT for childhood obesity. Data were collected at baseline and post-treatment. Binary logistic regression was used to assess associations between parent binge eating symptoms, depressive symptoms, and attrition. Results showed that parent binge eating symptoms (p=0.02), but not depressive symptoms (p=0.07), were significantly associated with attrition, after controlling for parent BMI, treatment group assignment, and family income. Higher reported parent binge eating symptoms were significantly related to attrition in FBT. Assessment of parent binge eating may be important in identifying families at risk for dropping out of FBT. Further, FBT may need to be adapted for families with parents who have a high level of psychopathology.

Some observations on attrition of students from canadian medical schools.

PubMed

Anderson, D O; Riches, E

1967-03-18

Students who entered their freshman year for the first time in 1958 and in 1959, from all medical schools in Canada, and those entering the four Western schools in 1960 were studied from the time they matriculated until they either graduated or withdrew from medical school. The rate of attrition is about 15% of matriculants each year, with the lowest rate at the University of Western Ontario (1.7%) and the highest at the University of Ottawa (33.6%) over the time period studied. Attrition was classified as academic and non-academic. Significantly higher rates were found in the case of non-academic attrition for women and in the case of academic attrition for Commonwealth students. Significantly higher rates for both types of attrition were found for older students and students who had attended undergraduate colleges different from their medical school colleges. It would appear from available statistics that the factors which combine to produce attrition are the intellectual and personality characteristics of the student, school promotional policies and evaluation methods.

Effect of severe plastic deformation on microstructure and mechanical properties of magnesium and aluminium alloys in wide range of strain rates

NASA Astrophysics Data System (ADS)

Skripnyak, Vladimir; Skripnyak, Evgeniya; Skripnyak, Vladimir; Vaganova, Irina; Skripnyak, Nataliya

2013-06-01

Results of researches testify that a grain size have a strong influence on the mechanical behavior of metals and alloys. Ultrafine grained HCP and FCC metal alloys present higher values of the spall strength than a corresponding coarse grained counterparts. In the present study we investigate the effect of grain size distribution on the flow stress and strength under dynamic compression and tension of aluminium and magnesium alloys. Microstructure and grain size distribution in alloys were varied by carrying out severe plastic deformation during the multiple-pass equal channel angular pressing, cyclic constrained groove pressing, and surface mechanical attrition treatment. Tests were performed using a VHS-Instron servo-hydraulic machine. Ultra high speed camera Phantom V710 was used for photo registration of deformation and fracture of specimens in range of strain rates from 0,01 to 1000 1/s. In dynamic regime UFG alloys exhibit a stronger decrease in ductility compared to the coarse grained material. The plastic flow of UFG alloys with a bimodal grain size distribution was highly localized. Shear bands and shear crack nucleation and growth were recorded using high speed photography.

Dissecting the mechanism of martensitic transformation via atomic-scale observations.

PubMed

Yang, Xu-Sheng; Sun, Sheng; Wu, Xiao-Lei; Ma, Evan; Zhang, Tong-Yi

2014-08-21

Martensitic transformation plays a pivotal role in the microstructural evolution and plasticity of many engineering materials. However, so far the underlying atomic processes that accomplish the displacive transformation have been obscured by the difficulty in directly observing key microstructural signatures on atomic scale. To resolve this long-standing problem, here we examine an AISI 304 austenitic stainless steel that has a strain/microstructure-gradient induced by surface mechanical attrition, which allowed us to capture in one sample all the key interphase regions generated during the γ(fcc) → ε(hcp) → α'(bcc) transition, a prototypical case of deformation induced martensitic transformation (DIMT). High-resolution transmission electron microscopy (HRTEM) observations confirm the crucial role of partial dislocations, and reveal tell-tale features including the lattice rotation of the α' martensite inclusion, the transition lattices at the ε/α' interfaces that cater the shears, and the excess reverse shear-shuffling induced γ necks in the ε martensite plates. These direct observations verify for the first time the 50-year-old Bogers-Burgers-Olson-Cohen (BBOC) model, and enrich our understanding of DIMT mechanisms. Our findings have implications for improved microstructural control in metals and alloys.

Dissecting the Mechanism of Martensitic Transformation via Atomic-Scale Observations

PubMed Central

Yang, Xu-Sheng; Sun, Sheng; Wu, Xiao-Lei; Ma, Evan; Zhang, Tong-Yi

2014-01-01

Martensitic transformation plays a pivotal role in the microstructural evolution and plasticity of many engineering materials. However, so far the underlying atomic processes that accomplish the displacive transformation have been obscured by the difficulty in directly observing key microstructural signatures on atomic scale. To resolve this long-standing problem, here we examine an AISI 304 austenitic stainless steel that has a strain/microstructure-gradient induced by surface mechanical attrition, which allowed us to capture in one sample all the key interphase regions generated during the γ(fcc) → ε(hcp) → α′(bcc) transition, a prototypical case of deformation induced martensitic transformation (DIMT). High-resolution transmission electron microscopy (HRTEM) observations confirm the crucial role of partial dislocations, and reveal tell-tale features including the lattice rotation of the α′ martensite inclusion, the transition lattices at the ε/α′ interfaces that cater the shears, and the excess reverse shear-shuffling induced γ necks in the ε martensite plates. These direct observations verify for the first time the 50-year-old Bogers-Burgers-Olson-Cohen (BBOC) model, and enrich our understanding of DIMT mechanisms. Our findings have implications for improved microstructural control in metals and alloys. PMID:25142283

Nanostructured antistatic and antireflective thin films made of indium tin oxide and silica over-coat layer

NASA Astrophysics Data System (ADS)

Cho, Young-Sang; Hong, Jeong-Jin; Yang, Seung-Man; Choi, Chul-Jin

2010-08-01

Stable dispersion of colloidal indium tin oxide nanoparticles was prepared by using indium tin oxide nanopowder, organic solvent, and suitable dispersants through attrition process. Various comminution parameters during the attrition step were studied to optimize the process for the stable dispersion of indium tin oxide sol. The transparent and conductive films were fabricated on glass substrate using the indium tin oxide sol by spin coating process. To obtain antireflective function, partially hydrolyzed alkyl silicate was deposited as over-coat layer on the pre-fabricated indium tin oxide film by spin coating technique. This double-layered structure of the nanostructured film was characterized by measuring the surface resistance and reflectance spectrum in the visible wavelength region. The final film structure was enough to satisfy the TCO regulations for EMI shielding purposes.

Prevalence and Causes of Attrition Among Surgical Residents: A Systematic Review and Meta-analysis.

PubMed

Khoushhal, Zeyad; Hussain, Mohamad A; Greco, Elisa; Mamdani, Muhammad; Verma, Subodh; Rotstein, Ori; Tricco, Andrea C; Al-Omran, Mohammed

2017-03-01

Attrition of residents from general surgery training programs is relatively high; however, there are wide discrepancies in the prevalence and causes of attrition reported among surgical residents in previous studies. To summarize the estimate of attrition prevalence among general surgery residents. We searched the Medline, EMBASE, Cochrane, PsycINFO, and ERIC databases (January 1, 1946, to October 22, 2015) for studies reporting on the prevalence and causes of attrition in surgical residents, as well as the characteristics and destinations of residents who left general surgery training programs. Database searches were conducted on October 22, 2015. Eligibility criteria included all studies reporting on the primary (attrition prevalence) or secondary (causes of attrition and characteristics and destination of residents who leave residency programs) outcomes in peer-reviewed journals. Commentaries, reviews, and studies reporting on preliminary surgery programs were excluded. Of the 41 full-text articles collected from the title/abstract screening, 22 studies (53.7%) met the selection criteria. Two reviewers independently collected and summarized the data. We calculated pooled estimates using random effects meta-analyses where appropriate. Attrition prevalence of general surgery residents. Overall, we included 22 studies that reported on residents (n = 19 821) from general surgery programs. The pooled estimate for the overall attrition prevalence among general surgery residents was 18% (95% CI, 14%-21%), with significant between-study variation (I2 = 96.8%; P < .001). Attrition was significantly higher among female compared with male (25% vs 15%, respectively; P = .008) general surgery residents, and most residents left after their first postgraduate year (48%; 95% CI, 39%-57%). Departing residents often relocated to another general surgery program (20%; 95% CI, 15%-24%) or switched to anesthesia (13%; 95% CI, 11%-16%) and other specialties. The most common reported causes of attrition were uncontrollable lifestyle (range, 12%-87.5%) and transferring to another specialty (range, 19%-38.9%). General surgery programs have relatively high attrition, with female residents more likely to leave their training programs than male residents. Residents most often relocate or switch to another specialty after the first postgraduate year owing to lifestyle-related issues.

Alarming attrition rates among HIV-infected individuals in pre-antiretroviral therapy care in Myanmar, 2011-2014.

PubMed

Oo, Myo Minn; Gupta, Vivek; Aung, Thet Ko; Kyaw, Nang Thu Thu; Oo, Htun Nyunt; Kumar, Ajay Mv

2016-01-01

High retention rates have been documented among patients receiving antiretroviral therapy (ART) in Myanmar. However, there is no information on human immunodeficiency virus (HIV)-infected individuals in care before initiation of ART (pre-ART care). We assessed attrition (loss-to-follow-up [LTFU] and death) rates among HIV-infected individuals in pre-ART care and their associated factors over a 4-year period. In this retrospective cohort study, we extracted routinely collected data of HIV-infected adults (>15 years old) entering pre-ART care (June 2011-June 2014) as part of an Integrated HIV Care (IHC) programme, Myanmar. Attrition rates per 100 person-years and cumulative incidence of attrition were calculated. Factors associated with attrition were examined by calculating hazard ratios (HRs). Of 18,037 HIV-infected adults enrolled in the IHC programme, 11,464 (63%) entered pre-ART care (60% men, mean age 37 years, median cluster of differentiation 4 (CD4) cell count 160 cells/µL). Of the 11,464 eligible participants, 3,712 (32%) underwent attrition of which 43% were due to deaths and 57% were due to LTFU. The attrition rate was 78 per 100 person-years (95% CI, 75-80). The cumulative incidence of attrition was 70% at the end of a 4-year follow-up, of which nearly 90% occurred in the first 6 months. Male sex (HR 1.5, 95% CI 1.4-1.6), WHO clinical Stage 3 and 4, CD4 count <200 cells/µL, abnormal BMI, and anaemia were statistically significant predictors of attrition. Pre-ART care attrition among persons living with HIV in Myanmar was alarmingly high - with most attrition occurring within the first 6 months. Strategies aimed at improving early HIV diagnosis and initiation of ART are needed. Suggestions include comprehensive nutrition support and intensified monitoring to prevent pre-ART care attrition by tracking patients who do not return for pre-ART care appointments. It is high time that Myanmar moves towards a 'test and treat' approach and ultimately eliminates the need for pre-ART care.

Interaction between attrition,abrasion and erosion in tooth wear.

PubMed

Addy, M; Shellis, R P

2006-01-01

Tooth wear is the result of three processes: abrasion (wear produced by interaction between teeth and other materials), attrition (wear through tooth-tooth contact) and erosion (dissolution of hard tissue by acidic substances). A further process (abfraction) might potentiate wear by abrasion and/or erosion. Both clinical and experimental observations show that individual wear mechanisms rarely act alone but interact with each other. The most important interaction is the potentiation of abrasion by erosive damage to the dental hard tissues. This interaction seems to be the major factor in occlusal and cervical wear. The available evidence seems insufficient to establish whether abfraction is an important contributor to tooth wear in vivo. Saliva can modulate erosive/abrasive tooth wear through formation of pellicle and by remineralisation but cannot prevent it.

Attrition in NRG Oncology's Radiation-Based Clinical Trials.

PubMed

Ulrich, Connie M; Deshmukh, Snehal; Pugh, Stephanie L; Hanlon, Alexandra; Grady, Christine; Watkins Bruner, Deborah; Curran, Walter

2018-05-10

To determine individual, organizational, and protocol-specific factors associated with attrition in NRG Oncology's radiation-based clinical trials. This retrospective analysis included 27,443 patients representing 134 NRG Oncology's radiation-based clinical trials .trials with primary efficacy results published from 1985-2011. Trials were separated on the basis of the primary endpoint (fixed time vs event driven). The cumulative incidence approach was used to estimate time to attrition, and cause-specific Cox proportional hazards models were used to assess factors associated with attrition. Most patients (69%) were enrolled in an event-driven trial (n = 18,809), while 31% were enrolled in a fixed-time trial (n = 8634). Median follow-up time for patients enrolled in fixed-time trials was 4.1 months and 37.2 months for patients enrolled in event-driven trials. Fixed time trials with a duration < 6 months had a 5 month attrition rate of 4.3% (95% confidence interval [CI]: 3.4%, 5.5%) and those with a duration ≥ 6 months had a 1 year attrition rate of 1.6% (95% CI: 1.2, 2.1). Event-driven trials had 1- and 5-year attrition rates of 0.5% (95% CI: 0.4%, 0.6%) and 13.6% (95% CI: 13.1%, 14.1%), respectively. Younger age, female gender, and Zubrod performance status >0 were associated with greater attrition as were enrollment by institutions in the West and South regions and participation in fixed-time trials. Attrition in clinical trials can have a negative effect on trial outcomes. Data on factors associated with attrition can help guide the development of strategies to enhance retention. These strategies should focus on patient characteristics associated with attrition in both fixed-time and event-driven trials as well as in differing geographic regions of the country. Copyright © 2018. Published by Elsevier Inc.

Attrition in graduate surgical education: an analysis of the 1993 entering cohort of surgical residents.

PubMed

Kwakwa, F; Jonasson, O

1999-12-01

Pyramidal surgical residency programs, in which more residents are enrolled than can complete the program, have gradually declined in number in recent years. In 1996, the Residency Review Committee for Surgery established a policy that the number of residents appointed to a program must be consistent with the number who will complete the program. Even so, there is still attrition in the ranks of surgical residents, some of whom hold undesignated preliminary positions and have no guarantee of a position that will lead to completion of the program. This study examined the 1993 entering cohort of surgical residents to determine the rate of attrition as of 1998. Data were collected from the AMA's Medical Education Research Information Database, the American College of Surgeons Resident Masterfile, and the Association of American Medical Colleges GME Tracking Census database. The data were examined by specialty, gender, ethnic background, and type of medical school attended. The overall attrition rate from surgical GME was 12%; the rate for international medical graduates was 33%; and the rate for osteopathic residents was 28%. African-American United States and Canadian graduates had attrition rates of 16% for men and 8% for women, and Hispanic United States and Canadian graduates had attrition rates of 14% for men and 15% for women. General surgery residents had an attrition rate of 26%, which included residents in undesignated preliminary positions. Gender was not a risk factor except for the significantly higher attrition rate of African-American men. Most (81%) of the residents who dropped out of surgical GME enrolled in GME in other specialties. The attrition rate from surgical GME is low, and most residents who drop out reenter GME in another specialty. Of concern is the high rate of attrition of African-American men who are United States or Canadian graduates. The highest rate of attrition, by far, is in the group of international medical graduates, many of whom are likely to have held undesignated preliminary positions.

Reducing fischer-tropsch catalyst attrition losses in high agitation reaction systems

DOEpatents

Singleton, Alan H.; Oukaci, Rachid; Goodwin, James G.

2001-01-01

A method for reducing catalyst attrition losses in hydrocarbon synthesis processes conducted in high agitation reaction systems; a method of producing an attrition-resistant catalyst; a catalyst produced by such method; a method of producing an attrition-resistant catalyst support; and a catalyst support produced by such method. The inventive method of reducing catalyst attrition losses comprises the step of reacting a synthesis gas in a high agitation reaction system in the presence of a catalyst. In one aspect, the catalyst preferably comprises a .gamma.-alumina support including an amount of titanium effective for increasing the attrition resistance of the catalyst. In another aspect, the catalyst preferably comprises a .gamma.-alumina support which has been treated, after calcination, with an acidic, aqueous solution. The acidic aqueous solution preferably has a pH of not more than about 5. In another aspect, the catalyst preferably comprises cobalt on a .gamma.-alumina support wherein the cobalt has been applied to the .gamma.-alumina support by totally aqueous, incipient wetness-type impregnation. In another aspect, the catalyst preferably comprises cobalt on a .gamma.-alumina support with an amount of a lanthana promoter effective for increasing the attrition resistance of the catalyst. In another aspect, the catalyst preferably comprises a .gamma.-alumina support produced from boehmite having a crystallite size, in the 021 plane, in the range of from about 30 to about 55 .ANG.ngstrons. In another aspect, the inventive method of producing an attrition-resistant catalyst comprises the step of treating a .gamma.-alumina support, after calcination of and before adding catalytic material to the support, with an acidic solution effective for increasing the attrition resistance of the catalyst. In another aspect, the inventive method of producing an attrition-resistant catalyst support comprises the step of treating calcined .gamma.-alumina with an acidic, aqueous solution effective for increasing the attrition resistance of the .gamma.-alumina.

Specific surface area as a maturity index of lunar fines

NASA Technical Reports Server (NTRS)

Gammage, R. B.; Holmes, H. F.

1975-01-01

Mature surface fines have an equilibrium specific surface area of about 0.6 sq m/g the equivalent mean particle size being about 3 microns. The adsorption behavior of inert gases (reversible isotherms) indicates that the particles are also nonporous in the size range of pores from 10 to 3000 A. Apparently, in mature soils there is a balance in the forces which cause fining, attrition, pore filling, and growth of lunar dust grains. Immature, lightly irradiated soils usually have coarser grains which reduce in size as aging proceeds. The specific surface area, determined by nitrogen or krypton sorption at 77 K, is a valuable index of soil maturity.

Predictors of Study Attrition in a Randomized Controlled Trial Evaluating a Perinatal Home-Visiting Program with Mothers with Psychosocial Vulnerabilities

PubMed Central

Foulon, Stéphanie; Greacen, Tim; Pasquet, Blandine; Dugravier, Romain; Saïas, Thomas; Guedeney, Nicole; Guedeney, Antoine; Tubach, Florence

2015-01-01

Objective Randomised controlled trials evaluating perinatal home-visiting programs are frequently confronted with the problem of high attrition rates. The aim of the present study is to identify predictors of study attrition in a trial evaluating a perinatal home-visiting program in France. Materials and Methods CAPEDP is a French randomized trial comparing a perinatal home-visiting program using psychologists versus usual care (N = 440). The first assessment was at inclusion into the trial at the 27th week of pregnancy and the final assessment when the child reached the age of two. Attrition rates were calculated at 3 and 24 months postpartum. Stepwise logistic regression was used to identify predictors of early (between inclusion and 3 months postpartum) and later (between 3 and 24 months postpartum) attrition among social, psychological and parenting factors. Results Attrition rates were 17% and 63% at 3 and 24 months respectively. At 24 months, there was significantly more attrition in the control arm (70.6%) compared to the intervention arm (55.2%). Five independent predictors of early attrition were identified: having already had an abortion; having greater attachment insecurity as measured with the Vulnerable Attachment Style Questionnaire (VASQ); having lower global severity of psychiatric symptoms as assessed with the Symptom Check-List (SCL-90) at inclusion, being neither currently employed nor studying; and declaring no tobacco consumption during pregnancy. Being randomized into the control arm, having undergone early parental loss before age 11 and having lower global severity of psychiatric symptoms (SCL-90) at 3 months postpartum were the only variables associated with later attrition. Conclusion This study provides key information for identifying mothers who may require specific support to avoid study attrition in trials evaluating a home-visiting program. PMID:26554839

Retention and Attrition Among African Americans in the STAR*D Study: What Causes Research Volunteers to Stay or Stray?

PubMed Central

Murphy, Eleanor J; Kassem, Layla; Chemerinski, Anat; Rush, A. John; Laje, Gonzalo; McMahon, Francis J.

2013-01-01

Background High attrition rates among African-Americans (AA) volunteers are a persistent problem that makes clinical trials less representative and complicates estimation of treatment outcomes. Many studies contrast AA with other ethnic/racial groups, but few compare the AA volunteers who remain in treatment with those who leave. Here, in addition to comparing patterns of attrition between African Americans and whites, we identify predictors of overall and early attrition among African Americans. Method Sample comprised non-Hispanic African-American (n=673) and white (n=2,549) participants in the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) study. Chi-square tests were used to examine racial group differences in reasons for exit. Multivariate logistic regression was used to examine predictors of overall attrition, early attrition (by Level 2) and top reasons cited for attrition among African Americans. Results For both African-American and white dropouts, non-compliance reasons for attrition were most commonly cited during the earlier phases of the study while reasons related to efficacy and medication side effects were cited later in the study. Satisfaction with treatment strongly predicted overall attrition among African Americans independent of socioeconomic, clinical, medical or psychosocial factors. Early attrition among African American dropouts was associated with less psychiatric comorbidity, and higher perceived physical functioning but greater severity of clinician-rated depression. Conclusions The decision to drop out is a dynamic process that changes over the course of a clinical trial. Strategies aimed at retaining African Americans in such trials should emphasize engagement with treatment and patient satisfaction immediately following enrollment and after treatment initiation. PMID:23723044

Retention and attrition among African Americans in the STAR*D study: what causes research volunteers to stay or stray?

PubMed

Murphy, Eleanor J; Kassem, Layla; Chemerinski, Anat; Rush, A John; Laje, Gonzalo; McMahon, Francis J

2013-11-01

High attrition rates among African-Americans (AA) volunteers are a persistent problem that makes clinical trials less representative and complicates estimation of treatment outcomes. Many studies contrast AA with other ethnic/racial groups, but few compare the AA volunteers who remain in treatment with those who leave. Here, in addition to comparing patterns of attrition between African Americans and Whites, we identify predictors of overall and early attrition among African Americans. Sample comprised non-Hispanic African-American (n = 673) and White (n = 2,549) participants in the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) study. Chi-square tests were used to examine racial group differences in reasons for exit. Multivariate logistic regression was used to examine predictors of overall attrition, early attrition (by level 2) and top reasons cited for attrition among African Americans. Both African-American and White dropouts most commonly cited noncompliance reasons for attrition during the earlier phases of the study, while citing reasons related to efficacy and medication side effects later in the study. Satisfaction with treatment strongly predicted overall attrition among African Americans independent of socioeconomic, clinical, medical or psychosocial factors. Early attrition among African American dropouts was associated with less psychiatric comorbidity, and higher perceived physical functioning but greater severity of clinician-rated depression. Compliance, efficacy, and side effects are important factors that vary in relative importance during the course of a clinical trial. For African Americans in such trials, retention strategies should be broadened to emphasize patient engagement and satisfaction during the critical periods immediately following enrollment and treatment initiation. © 2013 Wiley Periodicals, Inc.

Attrition from emergency medicine clinical practice in the United States.

PubMed

Ginde, Adit A; Sullivan, Ashley F; Camargo, Carlos A

2010-08-01

We estimate the annual attrition from emergency medicine clinical practice. We performed a cross-sectional analysis of the American Medical Association's 2008 Physician Masterfile, which includes data on all physicians who have ever obtained a medical license in at least 1 US state. We restricted the analysis to physicians who completed emergency medicine residency training or who obtained emergency medicine board certification. We defined attrition as not being active in emergency medicine clinical practice. Attrition was reported as cumulative and annualized rates, with stratification by years since training graduation. Death rates were estimated from life tables for the US population. Of the 30,864 emergency medicine-trained or emergency medicine board-certified physicians, 26,826 (87%) remain active in emergency medicine clinical practice. Overall, type of attrition was 45% to non-emergency medicine clinical practice, 22% retired, 14% administration, and 10% research/teaching. Immediate attrition (<2 years since training graduation) was 6.5%. The cumulative attrition rates from 2 to 15 years postgraduation were stable (5% to 9%) and thereafter were progressively higher, with 18% having left emergency medicine clinical practice at 20 years postgraduation and 25% at 30 years postgraduation. Annualized attrition rates were highest for the first 5 years postgraduation and after 40 years postgraduation; between 5 and 40 years, the rates remained low (<1%). The overall annual attrition rate from emergency medicine clinical practice, including estimated death rate, was approximately 1.7%. Despite the high stress and demands of emergency medicine, overall attrition remains low and compares favorably with that of other medical specialties. These data have positive implications for the emergency physician workforce and are important for accurate estimation of and planning for emergency physician workforce needs. 2009 American College of Emergency Physicians. Published by Mosby, Inc. All rights reserved.

A Correlational Study of a Reading Comprehension Program and Attrition Rates of ESL Nursing Students in Texas.

PubMed

Donnell, Wendy M

The purpose of this study was to examine the associations between English as a second language (ESL), a reading comprehension program, and attrition rates of nursing students. Higher attrition rates of ESL nursing students are an assumption, seemingly based on anecdotal evidence. Data reflecting ESL student attrition should be measured and analyzed so that students can be identified prior to attrition. A secondary analysis of a large database of 27 initial licensure programs in Texas was completed. Data analysis identified that ESL students who used a reading comprehension program were almost twice as likely to be off track or out of the program as ESL students who did not use the program. Nurse educators need to evaluate student profile characteristics in a comprehensive way when determining risk of attrition.

Derivation and Evaluation of a Risk-Scoring Tool to Predict Participant Attrition in a Lifestyle Intervention Project.

PubMed

Jiang, Luohua; Yang, Jing; Huang, Haixiao; Johnson, Ann; Dill, Edward J; Beals, Janette; Manson, Spero M; Roubideaux, Yvette

2016-05-01

Participant attrition in clinical trials and community-based interventions is a serious, common, and costly problem. In order to develop a simple predictive scoring system that can quantify the risk of participant attrition in a lifestyle intervention project, we analyzed data from the Special Diabetes Program for Indians Diabetes Prevention Program (SDPI-DP), an evidence-based lifestyle intervention to prevent diabetes in 36 American Indian and Alaska Native communities. SDPI-DP participants were randomly divided into a derivation cohort (n = 1600) and a validation cohort (n = 801). Logistic regressions were used to develop a scoring system from the derivation cohort. The discriminatory power and calibration properties of the system were assessed using the validation cohort. Seven independent factors predicted program attrition: gender, age, household income, comorbidity, chronic pain, site's user population size, and average age of site staff. Six factors predicted long-term attrition: gender, age, marital status, chronic pain, site's user population size, and average age of site staff. Each model exhibited moderate to fair discriminatory power (C statistic in the validation set: 0.70 for program attrition, and 0.66 for long-term attrition) and excellent calibration. The resulting scoring system offers a low-technology approach to identify participants at elevated risk for attrition in future similar behavioral modification intervention projects, which may inform appropriate allocation of retention resources. This approach also serves as a model for other efforts to prevent participant attrition.

Damage Analysis of Tensile Deformation of Co-rolled SMATed 304SS

NASA Astrophysics Data System (ADS)

Guo, X.; Leung, A. Y. T.; Chen, A.; Ruan, H.; Lu, J.

2010-05-01

One of recent experimental progresses in strengthening and toughening metals simultaneously is to adopt techniques of surface mechanical attrition treatment (SMAT) and warm co-rolling to 304 stainless steel (SS). To capture deformation behavior and associated damage initiation/evolution process in the co-rolled SMATed 304SS, cohesive finite element method (CFEM) is employed in this paper and simulation results are in agreement with experimental results. Both strengthening effect due to high yield stress of the nanograin layer and toughening effect due to non-localized damage in the nanograin layer are captured. Effect of energy release rate of nanograin layer on failure strain of layered co-rolled SMATed 304SS is investigated. It is found that the more brittle the nanograin layer is, the more potential necking sites in the nanograin layer are, and the more ductile the layered co-rolled SMATed 304SS is.

Bauschinger Effect and Back Stress in Gradient Cu-Ge Alloy

NASA Astrophysics Data System (ADS)

Hu, Xianzhi; Jin, Shenbao; Zhou, Hao; Yin, Zhe; Yang, Jian; Gong, Yulan; Zhu, Yuntian; Sha, Gang; Zhu, Xinkun

2017-09-01

Using surface mechanical attrition treatment (SMAT), a gradient structure composed of two gradient structure (GS) layers and a coarse grain (CG) layer was generated from a Cu-5.7 wt pct Ge alloy, significantly improving the yield strength of the sample. Unloading-reloading tests showed an unusual Bauschinger effect in these GS samples. The back stresses caused by the accumulated geometrically necessary dislocations (GNDs) on the GS/CG border increased with increasing strain. As found by electron backscatter diffraction (EBSD), the GNDs are mainly distributed in the gradient structured layer, and the density of the GNDs increase with increasing SMAT time. The effect of the back stress increased with increasing SMAT processing time due to the increase in the strain gradient. The pronounced Bauschinger effect in a GS sample can improve the resistance to forward plastic flow and finally contributes to the high strength of GS samples.

A difference in perspective--the North American and European interpretations of tooth wear.

PubMed

Bartlett, D; Phillips, K; Smith, B

1999-01-01

There is considerable interest in the European dental research literature about the problem of tooth wear and specifically about dental erosion, but this interest does not appear to be matched in North America based on the volume of the literature there. The purpose of this article is to consider the possible explanations for this difference. This article examines the reasons for this disparity and attempts to explain the difference by reviewing the North American and European literature on the etiology, pathogenesis, and prevalence of tooth wear. It would appear from the literature that the reason for the difference in interest between the 2 continents is a reflection of how the appearance, etiology, and terminology are interpreted and used to define tooth wear, attrition, and erosion. Attrition is the wear of teeth against teeth; therefore, by definition any worn surface that does not contact the opposing tooth must have another etiology. An appropriate descriptive term is "tooth wear" when the etiology is multifactorial or cannot be determined. A search of the literature shows more studies in the European literature of the etiology and prevalence of tooth wear than in the North American literature. The thrust of the European studies supports the view that erosion is more important than attrition in the etiology of tooth wear.

Childhood Exposure to Family Violence and Attrition in the Navy

DTIC Science & Technology

2003-02-01

in Treatment of Child Abuse : Common Ground for Mental Health, Medical, and Legal Practitioners, pp. 135-154. Baltimore MD Johns Hopkins University...was associated with early attrition whereas CPA and DV were unrelated to timing of attrition. 14. SUBJECT TERMS attrition, family violence, child ... abuse , recruits 16. SECURITY CLASSIFICATION OF: 18a. NAME OF RESPONSIBLE PERSON Commanding Officer a. REPORT UNCL b.ABSTRACT UNCL C. THIS

United States Marine Corps Reserve First Term Attrition Characteristics

DTIC Science & Technology

2012-03-01

This indicates if enlistees are older when they enter, they are more likely to attrite than are younger enlistees, which is consistent with previous...Pre-9/11 cohort. When comparing the two models on demographics, both predicted increased attrition for the older age at enlistment, females over...AFQT) scores and those without High School (HS) diplomas. Women have attrition rates twice that of men with similar AFQT scores, education, and

Student Attrition in Higher Education: Development of an Instrument to Assess Attrition Factors in Distance Learning Only Educational Environments

ERIC Educational Resources Information Center

York, Jessica Ann

2014-01-01

The purpose of this mixed methods study was to discover the factors and experiences that impact attrition in DLOEEs and to develop an instrument to assess them. Student attrition, those who do not persist voluntarily or involuntarily, occurs in all facets of higher education. In the last five years, the most growth in enrollments has occurred in…

Predictors of Short- and Long-Term Attrition From the Parents as Agents of Change Randomized Controlled Trial for Managing Pediatric Obesity.

PubMed

Spence, Nicholas D; Newton, Amanda S; Keaschuk, Rachel A; Ambler, Kathryn A; Jetha, Mary M; Holt, Nicholas L; Rosychuk, Rhonda J; Spence, John C; Sharma, Arya M; Ball, Geoff D C

Attrition in pediatric weight management is a substantial problem. This study examined factors associated with short- and long-term attrition from a lifestyle and behavioral intervention for parents of children with overweight or obesity. Fifty-two families with children ages 6 to 12 years old and body mass index at or above the 85th percentile participated in a randomized controlled trial focused on parents, comparing parent-based cognitive behavioral therapy with parent-based psychoeducation for pediatric weight management. We examined program attrition using two clinical phases of the intervention: short-term and long-term attrition, modeled using the general linear model. Predictors included intervention type, child/parent weight status, sociodemographic factors, and health of the family system. Higher self-assessed health of the family system was associated with lower short-term attrition; higher percentage of intervention sessions attended by parents was associated with lower long-term attrition. Different variables were significant in our short- and long-term models. Attrition might best be conceptualized based on short- and long-term phases of clinical, parent-based interventions for pediatric weight management. Copyright © 2016 National Association of Pediatric Nurse Practitioners. Published by Elsevier Inc. All rights reserved.

Attrition from active airman status during 1970.

DOT National Transportation Integrated Search

1972-03-01

Attrition from an active airman status amounts to approximately 17% annually. Summary data presented have served to quantify, to some extent, the characteristics of airmen medically certified during 1968 subsequently becoming attrition during 1970. T...

Attrition of limestone by impact loading in fluidized beds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fabrizio Scala; Fabio Montagnaro; Piero Salatino

2007-09-15

The present study addresses limestone attrition and fragmentation associated with impact loading, a process which may occur extensively in various regions of fluidized bed (FB) combustors/gasifiers, primarily the jetting region of the bottom bed, the exit region of the riser, and the cyclone. An experimental protocol for the characterization of the propensity of limestone to undergo attrition/fragmentation by impact loading is reported. The application of the protocol is demonstrated with reference to an Italian limestone whose primary fragmentation and attrition by surface wear have already been characterized in previous studies. The experimental procedure is based on the characterization of themore » amount and particle size distribution of the debris generated upon the impact of samples of sorbent particles against a target. Experiments were carried out at a range of particle impact velocities between 10 and 45 m/s, consistent with jet velocities corresponding to typical pressure drops across FB gas distributors. The protocol has been applied to either raw or preprocessed limestone samples. In particular, the effect of calcination, sulfation, and calcination/recarbonation cycles on the impact damage suffered by sorbent particles has been assessed. The measurement of particle voidage and pore size distribution by mercury intrusion was also accomplished to correlate fragmentation with the structural properties of the sorbent samples. Fragmentation by impact loading of the limestone is significant. Lime displays the largest propensity to undergo impact damage, followed by the sorbent sulfated to exhaustion, the recarbonated sorbent, and the raw limestone. Fragmentation of the raw limestone and of the sulfated lime follows a pattern typical of the failure of brittle materials. The fragmentation behavior of lime and recarbonated lime better conforms to a disintegration failure mode, with an extensive generation of very fine fragments. 27 refs., 9 figs. 1 tab.« less

A preliminary study to find a possible association between occlusal wear and maximum bite force in humans.

PubMed

Jain, Veena; Mathur, Vijay Prakash; Kumar, Abhishek

2013-01-01

The objective of the study was to investigate whether moderate-to-severe attrition is associated with maximum bite force in the first molar region. Maximum bite force in the first molar region was measured for a total of 60 subjects having moderate-to-severe attrition of occlusal surface (experimental group) using a specially-designed piezoelectric sensor based bite force measuring device. An equal number of age, gender, height and weight matched controls (control group) were also subjected to bite force measurement for comparison. The maximum bite force was found to be significantly lower (p < 0.05) in the experimental group [480.32 (153.40)] as compared to the controls [640.63 (148.90)]. While analyzing the possible etiology for occlusal wear mainly two reasons were elicited, i.e. history of parafunctional habits like use of known abrasive tooth powder (sub-group A) and Bruxism (sub-group B). However, there were many subjects in which no known definite etiological factors be attributed to occlusal wear (sub-group C). On analysing further with respect to the possibly correlated etiological factors with maximum bite force, no significant difference was found within the experimental sub-group. However, all three experimental sub-groups had significantly lower maximum bite force as compared to age, gender and BMI matched controls. A significantly lower maximum bite force was found to be associated with moderate-to-severe attrition as compared to subjects without attrition. However, no specific relation could be found between bite force and possible etiological factors like history of parafunctional habits, history of use of known abrasive tooth powder, etc.

A successful approach to minimizing attrition in racial/ethnic minority, low-income populations.

PubMed

Flores, Glenn; Portillo, Alberto; Lin, Hua; Walker, Candy; Fierro, Marco; Henry, Monica; Massey, Kenneth

2017-03-01

Recruiting and retaining minority participants in clinical trials continue to be major challenges. Although multiple studies document lower minority trial enrollment, much less is known about effective minority retention strategies. Our objectives were to evaluate an innovative approach to high RCT retention of minority children, and identify child/caregiver characteristics predicting attrition. The Kids' HELP trial examined the effects of Parent Mentors on insuring uninsured minority children. We tested a retention strategic framework consisting of: 1) optimizing cultural/linguistic competency; 2) staff training on participant relationships and trust; 3) comprehensive participant contact information; 4) an electronic tracking database; 5) reminders for upcoming outcomes-assessment appointments; 6) frequent, sustained contact attempts for non-respondents; 7) financial incentives; 8) individualized rapid-cycle quality-improvement approaches to non-respondents; 9) reinforcing study importance; and 10) home assessment visits. We compared attrition in Kids' HELP vs. two previous RCTs in similar populations, and conducted bivariate and multivariable analyses of factors associated with Kids' HELP attrition. Attrition in Kids' HELP was lower than in two similar RCTs, at 10.9% vs. 37% and 40% ( P <0.001). After multivariable adjustment, missing the first outcomes follow-up assessment was the only factor significantly associated with attrition (relative risk=1.5; 95% confidence interval, 1.1-2.0). A retention strategic framework was successful in minimizing attrition in minority, low-income children. Participants missing first assessment appointments were at highest risk of subsequent attrition. These findings suggest that deploying this framework may help RCT retention of low-income minority children, particularly those at the highest risk of subsequent attrition.

Review of attrition and adherence in exercise studies following hematopoietic stem cell transplantation.

PubMed

Hacker, Eileen Danaher; Mjukian, Maral

2014-04-01

Implementing exercise programs in people receiving high-dose chemotherapy followed by bone marrow (BMT) or hematopoietic stem cell transplantation (SCT) presents unique challenges. This review examines subject attrition rates and reasons for attrition as well as adherence to exercise interventions following BMT/SCT. Studies published between January 1985 and December 2012 that prospectively tested an exercise intervention following BMT or SCT were included in the review. Evaluation criteria included: (1) exercise modality; (2) the amount of supervision required to implement the intervention; (3) timing of the intervention; (4) subject attrition rates and reasons for attrition; and (5) exercise adherence rates. Of the 20 studies reviewed, most tested an aerobic exercise intervention or a combination of aerobic and strength training. Supervised exercise sessions were more commonly used than unsupervised sessions. The overall attrition rate was 18% for the 998 subjects enrolled in the studies. Major reasons for attrition included death, change in health status, protocol issues, personal issues with subjects, and lost to follow-up/no reason provided. Authors of supervised exercise programs rarely published exercise adherence information. Unsupervised exercise programs relied mainly on self-report to document adherence. Exercise research following BMT/SCT is becoming more sophisticated as researchers build upon the expanding literature base. Questions regarding subject attrition and adherence to exercise interventions must be addressed to identify interventions that are likely to be successful when translated into clinical practice. Subject attrition from exercise studies following BMT/SCT is relatively low. Adherence information for exercise interventions needs to be regularly addressed. Copyright © 2013 Elsevier Ltd. All rights reserved.

Forms of attrition in a longitudinal study of religion and health in older adults and implications for sample bias

PubMed Central

Hayward, R. David; Krause, Neal

2014-01-01

The use of longitudinal designs in the field of religion and health makes it important to understand how attrition bias may affect findings in this area. This study examines attrition in a 4-wave, 8-year study of older adults. Attrition resulted in a sample biased towards more educated and more religiously-involved individuals. Conditional linear growth curve models found that trajectories of change for some variables differed among attrition categories. Ineligibles had worsening depression, declining control, and declining attendance. Mortality was associated with worsening religious coping styles. Refusers experienced worsening depression. Nevertheless, there was no evidence of bias in the key religion and health results. PMID:25257794

Forms of Attrition in a Longitudinal Study of Religion and Health in Older Adults and Implications for Sample Bias.

PubMed

Hayward, R David; Krause, Neal

2016-02-01

The use of longitudinal designs in the field of religion and health makes it important to understand how attrition bias may affect findings in this area. This study examines attrition in a 4-wave, 8-year study of older adults. Attrition resulted in a sample biased toward more educated and more religiously involved individuals. Conditional linear growth curve models found that trajectories of change for some variables differed among attrition categories. Ineligibles had worsening depression, declining control, and declining attendance. Mortality was associated with worsening religious coping styles. Refusers experienced worsening depression. Nevertheless, there was no evidence of bias in the key religion and health results.

Attrition and success rates of accelerated students in nursing courses: a systematic review.

PubMed

Doggrell, Sheila Anne; Schaffer, Sally

2016-01-01

There is a comprehensive literature on the academic outcomes (attrition and success) of students in traditional/baccalaureate nursing programs, but much less is known about the academic outcomes of students in accelerated nursing programs. The aim of this systematic review is to report on the attrition and success rates (either internal examination or NCLEX-RN) of accelerated students, compared to traditional students. For the systematic review, the databases (Pubmed, Cinahl and PsychINFO) and Google Scholar were searched using the search terms 'accelerated' or 'accreditation for prior learning', 'fast-track' or 'top up' and 'nursing' with 'attrition' or 'retention' or 'withdrawal' or 'success' from 1994 to January 2016. All relevant articles were included, regardless of quality. The findings of 19 studies of attrition rates and/or success rates for accelerated students are reported. For international accelerated students, there were only three studies, which are heterogeneous, and have major limitations. One of three studies has lower attrition rates, and one has shown higher success rates, than traditional students. In contrast, another study has shown high attrition and low success for international accelerated students. For graduate accelerated students, most of the studies are high quality, and showed that they have rates similar or better than traditional students. Thus, five of six studies have shown similar or lower attrition rates. Four of these studies with graduate accelerated students and an additional seven studies of success rates only, have shown similar or better success rates, than traditional students. There are only three studies of non-university graduate accelerated students, and these had weaknesses, but were consistent in reporting higher attrition rates than traditional students. The paucity and weakness of information available makes it unclear as to the attrition and/or success of international accelerated students in nursing programs. The good information available suggests that accelerated programs may be working reasonably well for the graduate students. However, the limited information available for non-university graduate students is weak, but consistent, in suggesting they may struggle in accelerated courses. Further studies are needed to determine the attrition and success rates of accelerated students, particularly for international and non-university graduate students.

40 CFR 1060.240 - How do I demonstrate that my emission family complies with evaporative emission standards?

Code of Federal Regulations, 2010 CFR

2010-07-01

... of the following control technologies: (1) A coextruded high-density polyethylene fuel tank with a... of 0.40 square meters may use high-permeation gasket material representing a surface area of up to 1...). The carbon must also pass a dust attrition test based on ASTM D3802 (incorporated by reference in...

The Role of Language Dominance in Cross-Linguistic Syntactic Influence: A Korean Child's Use of Null Subjects in Attriting English

ERIC Educational Resources Information Center

Kang, Sang-Gu

2013-01-01

While Hulk and Muller (2000) predict that the direction of cross-linguistic syntactic influence is unidirectional when the construction involves syntax-pragmatics interface and surface overlap between two languages, they explicitly rule out language dominance as a factor involved. This study questions their latter claim and argues that the syntax…

Assessment of U.S. Government and Coalition Efforts to Develop the Logistics Sustainment Capability of the Afghan National Army

DTIC Science & Technology

2014-12-19

enabled them to return home to work in the private sector at higher pay. The result was a considerable shortfall of trained mechanics at logistics...of reasons for the attrition of trained mechanics from the ANA, including higher pay and better benefits in the private sector , without the...removal and replacement of designated items (e.g. starters , radiators, etc.), and limited repairs to certain items. • General maintenance

A validation of the fibre orientation and fibre length attrition prediction for long fibre-reinforced thermoplastics

NASA Astrophysics Data System (ADS)

Hopmann, Ch.; Weber, M.; van Haag, J.; Schöngart, M.

2015-05-01

To improve the mechanical performance of polymeric parts, fibre reinforcement has established in industrial applications during the last decades. Next to the widely used Short Fibre-reinforced Thermoplastics (SFT) the use of Long Fibre-reinforced Thermoplastics (LFT) is increasingly growing. Especially for non-polar polymeric matrices like polypropylene (PP), longer fibres can significantly improve the mechanical performance. As with every kind of discontinuous fibre reinforcement the fibre orientations (FO) show a high impact on the mechanical properties. On the contrary to SFT where the local fibre length distribution (FLD) can be often neglected, for LFT the FLD show a high impact on the material's properties and has to be taken into account in equal measure to the FOD. Recently numerical models are available in commercial filling simulation software and allow predicting both the local FOD and FLD in LFT parts. The aim of this paper is to compare i.) the FOD results and ii) the FLD results from available orientation- and fibre length attrition-models to those obtained from experimental data. The investigations are conducted by the use of different injection moulded specimens made from long glass fibre reinforced PP. In order to determine the FOD, selected part sections are examined by means of Computed Tomographic (CT) analyses. The fully three dimensional measurement of the FOD is then performed by digital image processing using grey scale correlation. The FLD results are also obtained by using digital image processing after a thermal pyrolytic separation of the polymeric matrix from the fibres. Further the FOD and the FLD are predicted by using a reduced strain closure (RSC) as well as an anisotropic rotary diffusion - reduced strain closure model (ARD-RSC) and Phelps-Tucker fibre length attrition model implemented in the commercial filling software Moldflow, Autodesk Inc., San Rafael, CA, USA.

A validation of the fibre orientation and fibre length attrition prediction for long fibre-reinforced thermoplastics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hopmann, Ch.; Weber, M.; Haag, J. van

2015-05-22

To improve the mechanical performance of polymeric parts, fibre reinforcement has established in industrial applications during the last decades. Next to the widely used Short Fibre-reinforced Thermoplastics (SFT) the use of Long Fibre-reinforced Thermoplastics (LFT) is increasingly growing. Especially for non-polar polymeric matrices like polypropylene (PP), longer fibres can significantly improve the mechanical performance. As with every kind of discontinuous fibre reinforcement the fibre orientations (FO) show a high impact on the mechanical properties. On the contrary to SFT where the local fibre length distribution (FLD) can be often neglected, for LFT the FLD show a high impact on themore » material’s properties and has to be taken into account in equal measure to the FOD. Recently numerical models are available in commercial filling simulation software and allow predicting both the local FOD and FLD in LFT parts. The aim of this paper is to compare i.) the FOD results and ii) the FLD results from available orientation- and fibre length attrition-models to those obtained from experimental data. The investigations are conducted by the use of different injection moulded specimens made from long glass fibre reinforced PP. In order to determine the FOD, selected part sections are examined by means of Computed Tomographic (CT) analyses. The fully three dimensional measurement of the FOD is then performed by digital image processing using grey scale correlation. The FLD results are also obtained by using digital image processing after a thermal pyrolytic separation of the polymeric matrix from the fibres. Further the FOD and the FLD are predicted by using a reduced strain closure (RSC) as well as an anisotropic rotary diffusion - reduced strain closure model (ARD-RSC) and Phelps-Tucker fibre length attrition model implemented in the commercial filling software Moldflow, Autodesk Inc., San Rafael, CA, USA.« less

Microstructure evolution during helium irradiation and post-irradiation annealing in a nanostructured reduced activation steel

NASA Astrophysics Data System (ADS)

Liu, W. B.; Ji, Y. Z.; Tan, P. K.; Zhang, C.; He, C. H.; Yang, Z. G.

2016-10-01

Severe plastic deformation, intense single-beam He-ion irradiation and post-irradiation annealing were performed on a nanostructured reduced activation ferritic/martensitic (RAFM) steel to investigate the effect of grain boundaries (GBs) on its microstructure evolution during these processes. A surface layer with a depth-dependent nanocrystalline (NC) microstructure was prepared in the RAFM steel using surface mechanical attrition treatment (SMAT). Microstructure evolution after helium (He) irradiation (24.8 dpa) at room temperature and after post-irradiation annealing was investigated using Transmission Electron Microscopy (TEM). Experimental observation shows that GBs play an important role during both the irradiation and the post-irradiation annealing process. He bubbles are preferentially trapped at GBs/interfaces during irradiation and cavities with large sizes are also preferentially trapped at GBs/interfaces during post-irradiation annealing, but void denuded zones (VDZs) near GBs could not be unambiguously observed. Compared with cavities at GBs and within larger grains, cavities with smaller size and higher density are found in smaller grains. The average size of cavities increases rapidly with the increase of time during post-irradiation annealing at 823 K. Cavities with a large size are observed just after annealing for 5 min, although many of the cavities with small sizes also exist after annealing for 240 min. The potential mechanism of cavity growth behavior during post-irradiation annealing is also discussed.

Selective attrition and intraindividual variability in response time moderate cognitive change.

PubMed

Yao, Christie; Stawski, Robert S; Hultsch, David F; MacDonald, Stuart W S

2016-01-01

Selection of a developmental time metric is useful for understanding causal processes that underlie aging-related cognitive change and for the identification of potential moderators of cognitive decline. Building on research suggesting that time to attrition is a metric sensitive to non-normative influences of aging (e.g., subclinical health conditions), we examined reason for attrition and intraindividual variability (IIV) in reaction time as predictors of cognitive performance. Three hundred and four community dwelling older adults (64-92 years) completed annual assessments in a longitudinal study. IIV was calculated from baseline performance on reaction time tasks. Multilevel models were fit to examine patterns and predictors of cognitive change. We show that time to attrition was associated with cognitive decline. Greater IIV was associated with declines on executive functioning and episodic memory measures. Attrition due to personal health reasons was also associated with decreased executive functioning compared to that of individuals who remained in the study. These findings suggest that time to attrition is a useful metric for representing cognitive change, and reason for attrition and IIV are predictive of non-normative influences that may underlie instances of cognitive loss in older adults.

Selective Attrition and Intraindividual Variability in Response Time Moderate Cognitive Change

PubMed Central

Yao, Christie; Stawski, Robert S.; Hultsch, David F.; MacDonald, Stuart W.S.

2016-01-01

Objectives Selection of a developmental time metric is useful for understanding causal processes that underlie aging-related cognitive change, and for the identification of potential moderators of cognitive decline. Building on research suggesting that time to attrition is a metric sensitive to non-normative influences of aging (e.g., subclinical health conditions), we examined reason for attrition and intraindividual variability (IIV) in reaction time as predictors of cognitive performance. Method Three-hundred and four community dwelling older adults (64-92 years) completed annual assessments in a longitudinal study. IIV was calculated from baseline performance on reaction time tasks. Multilevel models were fit to examine patterns and predictors of cognitive change. Results We show that time to attrition was associated with cognitive decline. Greater IIV was associated with declines on executive functioning and episodic memory measures. Attrition due to personal health reasons was also associated with decreased executive functioning compared to individuals who remained in study. Discussion These findings suggest that time to attrition is a useful metric for representing cognitive change, and reason for attrition and IIV are predictive of non-normative influences that may underlie instances of cognitive loss in older adults. PMID:26647008

Does oxidative stress shorten telomeres?

PubMed

Boonekamp, Jelle J; Bauch, Christina; Mulder, Ellis; Verhulst, Simon

2017-05-01

Oxidative stress shortens telomeres in cell culture, but whether oxidative stress explains variation in telomere shortening in vivo at physiological oxidative stress levels is not well known. We therefore tested for correlations between six oxidative stress markers and telomere attrition in nestling birds (jackdaws Corvus monedula ) that show a high rate of telomere attrition in early life. Telomere attrition was measured between ages 5 and 30 days, and was highly variable (average telomere loss: 323 bp, CV = 45%). Oxidative stress markers were measured in blood at age 20 days and included markers of oxidative damage (TBARS, dROMs and GSSG) and markers of antioxidant protection (GSH, redox state, uric acid). Variation in telomere attrition was not significantly related to these oxidative stress markers (| r | ≤ 0.08, n = 87). This finding raises the question whether oxidative stress accelerates telomere attrition in vivo The accumulation of telomere attrition over time depends both on the number of cell divisions and on the number of base pairs lost per DNA replication and, based on our findings, we suggest that in a growing animal cell proliferation, dynamics may be more important for explaining variation in telomere attrition than oxidative stress. © 2017 The Author(s).

ART Attrition across Health Facilities Implementing Option B+ in Haiti.

PubMed

Myrtil, Martine Pamphile; Puttkammer, Nancy; Gloyd, Stephen; Robinson, Julia; Yuhas, Krista; Domercant, Jean Wysler; Honoré, Jean Guy; Francois, Kesner

2018-01-01

Describing factors related to high attrition is important in order to improve the implementation of the Option B+ strategy in Haiti. We conducted a retrospective cohort study to describe the variability of antiretroviral therapy (ART) retention across health facilities among pregnant and lactating women and assess for differences in ART retention between Option B+ clients and other ART patients. There were 1989 Option B+ clients who initiated ART in 45 health facilities. The percentage of attrition varied from 9% to 81% across the facilities. The largest health facilities had 38% higher risk of attrition (relative risk [RR]: 1.38, 95% confidence interval [CI]: 1.08-1.77, P = .009). Private institutions had 18% less risk of attrition (RR: 0.82, 95% CI: 0.70-0.96, P = .020). Health facilities located in the West department and the South region had lower risk of attrition. Being on treatment in a large or public health facility or a facility located in the North region was a significant risk factor associated with high attrition among Option B+ clients. The implementation of the Option B+ strategy must be reevaluated in order to effectively eliminate mother-to-child HIV transmission.

Predictors of early faculty attrition at one Academic Medical Center

PubMed Central

2014-01-01

Background Faculty turnover threatens the research, teaching and clinical missions of medical schools. We measured early attrition among newly-hired medical school faculty and identified personal and institutional factors associated with early attrition. Methods This retrospective cohort study identified faculty hired during the 2005–2006 academic year at one school. Three-year attrition rates were measured. A 40-question electronic survey measured demographics, career satisfaction, faculty responsibilities, institutional/departmental support, and reasons for resignation. Odds ratios (ORs) and 95 percent confidence intervals (95% CI) identified variables associated with early attrition. Results Of 139 faculty, 34% (95% CI = 26-42%) resigned within three years of hire. Attrition was associated with: perceived failure of the Department Chair to foster a climate of teaching, research, and service (OR = 6.03; 95% CI: 1.84, 19.69), inclusiveness, respect, and open communication (OR = 3.21; 95% CI: 1.04, 9.98). Lack of professional development of the faculty member (OR = 3.84; 95% CI: 1.25, 11.81); institutional recognition and support for excellence in teaching (OR = 2.96; 95% CI: 0.78, 11.19) and clinical care (OR = 3.87; 95% CI: 1.04, 14.41); and >50% of professional time devoted to patient care (OR = 3.93; 95% CI: 1.29, 11.93) predicted attrition. Gender, race, ethnicity, academic degree, department type and tenure status did not predict early attrition. Of still-active faculty, an additional 27 (48.2%, 95% CI: 35.8, 61.0) reported considering resignation within the 5 years. Conclusions In this pilot study, one-third of new faculty resigned within 3 years of hire. Greater awareness of predictors of early attrition may help schools identify threats to faculty career satisfaction and retention. PMID:24512629

A national study of attrition in general surgery training: which residents leave and where do they go?

PubMed

Yeo, Heather; Bucholz, Emily; Ann Sosa, Julie; Curry, Leslie; Lewis, Frank R; Jones, Andrew T; Viola, Kate; Lin, Zhenqui; Bell, Richard H

2010-09-01

Implementation of the 80-hour mandate was expected to reduce attrition from general surgery (GS) residency. This is the first quantitative report from a national prospective study of resident/program characteristics associated with attrition. Analysis included all categorical GS residents entered on American Board of Surgery residency rosters in 2007 to 2008. Cases of attrition were identified by program report, individually confirmed, and linked to demographic data from the National Study of Expectations and Attitudes of Residents in Surgery administered January 2008. All surgical categorical GS residents active on the 2007-2008 resident rosters (N = 6,303) were analyzed for attrition. Complete National Study of Expectations and Attitudes of Residents in Surgery demographic information was available for 3959; the total and survey groups were similar with regard to important characteristics. About 3% of US categorical residents resigned in 2007 to 2008, and 0.4% had contracts terminated. Across all years (including research), there was a 19.5% cumulative risk of resignation. Attrition was highest in PGY-1 (5.9%), PGY-2 (4.3%), and research year(s) (3.9%). Women were no more likely to leave programs than men (2.1% vs. 1.9%). Of several program/resident variables examined, postgraduate year-level was the only independent predictor of attrition in multivariate analysis. Residents who left GS whose plans were known most often pursued nonsurgical residencies (62%), particularly anesthesiology (21%) and radiology (11%). Only 13% left for surgical specialties. Attrition rates are high despite mandated work hour reductions; 1 in 5 GS categorical residents resigns, and most pursue nonsurgical careers. Demographic factors, aside from postgraduate year do not appear predictive. Residents are at risk for attrition early in training and during research, and this could afford educators a target for intervention.

Sleep bruxism in individuals with and without attrition-type tooth wear: An exploratory matched case-control electromyographic study.

PubMed

Jonsgar, Christine; Hordvik, Paul-Arne; Berge, Morten E; Johansson, Ann-Katrin; Svensson, Peter; Johansson, Anders

2015-12-01

To examine if there is a difference in possible sleep bruxism activity (SB) in subjects with or without attrition-type tooth wear. Sixteen individuals with pronounced attritional-type tooth wear were compared with sex and aged matched controls without tooth wear by means of measurement of electromyographic (EMG) activity during a minimum of four consecutive nights of sleep. Mean age and range for the study- and control- group was 23.7 years (range 19.9-28.5) and 23.6 years (range 20.3-27.9), respectively. There were 11 females and five males in each of the two groups. The attrition group presented incisal/occlusal attrition wear into dentin and matching wear facets between opposing anterior teeth. The controls had negligible signs of incisal/occlusal wear and a minimal number of matching wear facets. The prevalence of both self-reported and partner-reported SB was significantly more common in the attrition group compared to the controls (P=0.04 and P=0.007, respectively). Self-reported morning facial pain was similarly more common in the attrition group (P=0.014). Maximum opening capacity, number of muscles painful to palpation, salivary flow rate and buffering capacity were not significantly different between the groups. Interestingly, none of the measures of jaw muscle EMG activity during sleep, as recorded by the portable EMG equipment, differed significantly between the attrition group and the matched controls (P>0.05). The results from this exploratory study suggest that there is no difference in EMG activity between subjects with and without attrition-type tooth wear. Further research is needed in order to substantiate these preliminary findings. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

Incorporating the sampling design in weighting adjustments for panel attrition

PubMed Central

Chen, Qixuan; Gelman, Andrew; Tracy, Melissa; Norris, Fran H.; Galea, Sandro

2015-01-01

We review weighting adjustment methods for panel attrition and suggest approaches for incorporating design variables, such as strata, clusters and baseline sample weights. Design information can typically be included in attrition analysis using multilevel models or decision tree methods such as the CHAID algorithm. We use simulation to show that these weighting approaches can effectively reduce bias in the survey estimates that would occur from omitting the effect of design factors on attrition while keeping the resulted weights stable. We provide a step-by-step illustration on creating weighting adjustments for panel attrition in the Galveston Bay Recovery Study, a survey of residents in a community following a disaster, and provide suggestions to analysts in decision making about weighting approaches. PMID:26239405

Premilitary intimate partner violence and attrition from the U.S. Navy.

PubMed

Merrill, Lex L; Stander, Valerie A; Thomsen, Cynthia J; Crouch, Julie L; Milner, Joel S

2006-12-01

A prospective study of U.S. Navy recruits (N = 5,498) examined whether premilitary intimate partner violence (IPV) was associated with attrition. Overall, more than one-fourth of recruits reported premilitary physical IPV and more than two-thirds reported premilitary verbal IPV. Women reported more perpetration and receipt of IPV than men, and married or cohabiting respondents reported more IPV than single respondents. Both perpetration and receipt of IPV significantly predicted attrition within 4 years. However, after controlling for other forms of IPV, only receipt of physical IPV significantly predicted attrition. In only one analysis did associations between IPV and attrition vary according to marital status or gender; premilitary receipt of verbal IPV had different effects on women and men.

Effect of occlusal splint therapy on maximum bite force in individuals with moderate to severe attrition of teeth.

PubMed

Jain, Veena; Mathur, Vijay Prakash; Abhishek, Kumar; Kothari, Mohit

2012-10-01

The purpose of the pilot study was to determine the effect of restoring lost occlusal vertical dimension (OVD) due to attrition on maximum bite force in humans. A total of 124 subjects in age range of 25-40 years, with moderate to severe attrition, having full complement of teeth were screened according to inclusion and exclusion criteria. After consent, occlusal vertical dimension was assessed by employing mechanical and physiological methods in the experimental group and a maxillary canine guided hard splint was fabricated for each subjects fulfilling inclusion criteria and with positive consent (78). Bite force in experimental group was measured before, immediately after delivery of splint and subsequently at an interval of four, eight, and twelve weeks. Due loss during follow up, only 50 subjects could be available for bite force recording till 12 weeks. Bite force of age, gender, height and weight matched controls with no signs of attrition was also measured for comparison. Bite force of the experimental group was found to be significantly less than the matched controls (P=0.000) initially. After delivery of splint, bite force values increased progressively till twelve weeks. However comparison of bite force values of experimental group with control group showed no significant difference at end of eight (P=0.008) and twelve weeks (P=0.162). It was concluded that maximum bite force increases with restoration of lost vertical using splint therapy. A time period of 8-12 weeks is required to restore the maximum bite force value approximately similar to matched controls. Copyright © 2012 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.

Non-Traditional Transfer Student Attrition

ERIC Educational Resources Information Center

Monroe, Anne

2006-01-01

Current literature focuses on traditional student attrition and on transfer transition, but little information is available on the non-traditional transfer student experience. The following study explores the process of non-traditional transfer student attrition through an investigation that illustrates the importance of past student experiences,…

Cumulative stress in research animals: Telomere attrition as a biomarker in a welfare context?

PubMed

Bateson, Melissa

2016-02-01

Progress in improving animal welfare is currently limited by the lack of objective methods for assessing lifetime experience. I propose that telomere attrition, a cellular biomarker of biological age, provides a molecular measure of cumulative experience that could be used to assess the welfare impact of husbandry regimes and/or experimental procedures on non-human animals. I review evidence from humans that telomere attrition is accelerated by negative experiences in a cumulative and dose-dependent manner, but that this attrition can be mitigated or even reversed by positive life-style interventions. Evidence from non-human animals suggests that despite some specific differences in telomere biology, stress-induced telomere attrition is a robust phenomenon, occurring in a range of species including mice and chickens. I conclude that telomere attrition apparently integrates positive and negative experience in an accessible common currency that translates readily to novel species--the Holy Grail of a cumulative welfare indicator. © 2015 The Author. BioEssays published by WILEY Periodicals, Inc.

Cumulative stress in research animals: Telomere attrition as a biomarker in a welfare context?

PubMed Central

2015-01-01

Progress in improving animal welfare is currently limited by the lack of objective methods for assessing lifetime experience. I propose that telomere attrition, a cellular biomarker of biological age, provides a molecular measure of cumulative experience that could be used to assess the welfare impact of husbandry regimes and/or experimental procedures on non‐human animals. I review evidence from humans that telomere attrition is accelerated by negative experiences in a cumulative and dose‐dependent manner, but that this attrition can be mitigated or even reversed by positive life‐style interventions. Evidence from non‐human animals suggests that despite some specific differences in telomere biology, stress‐induced telomere attrition is a robust phenomenon, occurring in a range of species including mice and chickens. I conclude that telomere attrition apparently integrates positive and negative experience in an accessible common currency that translates readily to novel species – the Holy Grail of a cumulative welfare indicator. PMID:26645576

Self-esteem and self-efficacy as predictors of attrition in associate degree nursing students.

PubMed

Peterson-Graziose, Virginia; Bryer, Jennifer; Nikolaidou, Maria

2013-06-01

There is a serious and growing shortage of nurses in the United States, and the high rate of student attrition from nursing programs has further added to this problem. The challenge for schools of nursing is to recruit increased numbers of qualified candidates into their programs and to determine ways to decrease the rate of student attrition. The purpose of this study was to determine whether self-esteem, self-efficacy, and life stressors were significantly related to student attrition in first-semester associate degree nursing students. A descriptive correlational design and nonprobability convenience sample of first-semester associate degree nursing students was used. Data were gathered using the Rosenberg Self-Esteem Scale, the General Self-Efficacy Scale, and the Holmes and Rahe Social Readjustment Rating Scale. Findings indicated that self-esteem was significantly associated with student attrition. Results from this study provide the basis for targeted interventions designed to decrease student attrition rates in associate degree nursing programs. Copyright 2013, SLACK Incorporated.

Developmental telomere attrition predicts impulsive decision-making in adult starlings

PubMed Central

Bateson, Melissa; Brilot, Ben O.; Gillespie, Robert; Monaghan, Pat; Nettle, Daniel

2015-01-01

Animals in a poor biological state face reduced life expectancy, and as a consequence should make decisions that prioritize immediate survival and reproduction over long-term benefits. We tested the prediction that if, as has been suggested, developmental telomere attrition is a biomarker of state and future life expectancy, then individuals who have undergone greater developmental telomere attrition should display greater choice impulsivity as adults. We measured impulsive decision-making in a cohort of European starlings (Sturnus vulgaris) in which we had previously manipulated developmental telomere attrition by cross-fostering sibling chicks into broods of different sizes. We show that as predicted by state-dependent optimality models, individuals who had sustained greater developmental telomere attrition and who had shorter current telomeres made more impulsive foraging decisions as adults, valuing smaller, sooner food rewards more highly than birds with less attrition and longer telomeres. Our findings shed light on the biological embedding of early adversity and support a functional explanation for its consequences that could be applicable to other species, including humans. PMID:25473012

Oral breathing challenge in participants with vocal attrition.

PubMed

Sivasankar, Mahalakshmi; Fisher, Kimberly V

2003-12-01

Vocal folds undergo osmotic challenge by mouth breathing during singing, exercising, and loud speaking. Just 15 min of obligatory oral breathing, to dry the vocal folds, increases phonation threshold pressure (Pth) and expiratory vocal effort in healthy speakers (M. Sivasankar & K. Fisher, 2002). We questioned whether oral breathing is more detrimental to phonation in healthy participants with a history of temporary vocal attrition. The effects of a 15-min oral or nasal breathing challenge on Pth and perceived expiratory vocal effort were compared for participants reporting symptoms of vocal attrition (N = 18, ages 19-38 years) and normal controls (N = 20, ages 19-33 years). Post-challenge-prechallenge differences in Pth (deltaPth) and effort (deltaEffort) revealed that oral breathing, but not nasal breathing, increased Pth (p < .001 ) and effort (p < .001) at low, comfortable, and high pitch. deltaPth was significantly greater in participants with vocal attrition than in normal controls (p < .001). Nasal breathing reduced Pth for all controls but not for all participants reporting vocal attrition. deltaPth was significantly and linearly correlated with deltaEffort (rvocal attrition = .81, p < .001; rcontrol = .84, p < .001). We speculate that the greater increases in Pth in participants reporting vocal attrition may result from delayed or inadequate compensatory response to superficial laryngeal dehydration. Obligatory oral breathing may place voice users at risk for exacerbating vocal attrition. That sol layer depletion by obligatory oral breathing increased Pth and vocal effort provides support for the role of superficial hydration in maintaining ease of phonation.

Analysis of occlusal variables, dental attrition, and age for distinguishing healthy controls from female patients with intracapsular temporomandibular disorders.

PubMed

Seligman, D A; Pullinger, A G

2000-01-01

Confusion about the relationship of occlusion to temporomandibular disorders (TMD) persists. This study attempted to identify occlusal and attrition factors plus age that would characterize asymptomatic normal female subjects. A total of 124 female patients with intracapsular TMD were compared with 47 asymptomatic female controls for associations to 9 occlusal factors, 3 attrition severity measures, and age using classification tree, multiple stepwise logistic regression, and univariate analyses. Models were tested for accuracy (sensitivity and specificity) and total contribution to the variance. The classification tree model had 4 terminal nodes that used only anterior attrition and age. "Normals" were mainly characterized by low attrition levels, whereas patients had higher attrition and tended to be younger. The tree model was only moderately useful (sensitivity 63%, specificity 94%) in predicting normals. The logistic regression model incorporated unilateral posterior crossbite and mediotrusive attrition severity in addition to the 2 factors in the tree, but was slightly less accurate than the tree (sensitivity 51%, specificity 90%). When only occlusal factors were considered in the analysis, normals were additionally characterized by a lack of anterior open bite, smaller overjet, and smaller RCP-ICP slides. The log likelihood accounted for was similar for both the tree (pseudo R(2) = 29.38%; mean deviance = 0.95) and the multiple logistic regression (Cox Snell R(2) = 30.3%, mean deviance = 0.84) models. The occlusal and attrition factors studied were only moderately useful in differentiating normals from TMD patients.

Time Strengthening of Crystal Nanocontacts

NASA Astrophysics Data System (ADS)

Mazo, Juan J.; Dietzel, Dirk; Schirmeisen, Andre; Vilhena, J. G.; Gnecco, Enrico

2017-06-01

We demonstrate how an exponentially saturating increase of the contact area between a nanoasperity and a crystal surface, occurring on time scales governed by the Arrhenius equation, is consistent with measurements of the static friction and lateral contact stiffness on a model alkali-halide surface at different temperatures in ultrahigh vacuum. The "contact ageing" effect is attributed to atomic attrition and is eventually broken by thermally activated slip of the nanoasperity on the surface. The combination of the two effects also leads to regions of strengthening and weakening in the velocity dependence of the friction, which are well-reproduced by an extended version of the Prandtl-Tomlinson model.

Is Retrieval-Induced Forgetting behind the Bilingual Disadvantage in Word Production?

ERIC Educational Resources Information Center

Runnqvist, Elin; Costa, Albert

2012-01-01

Levy, Mc Veigh, Marful and Andreson (2007) found that naming pictures in L2 impaired subsequent recall of the L1 translation words. This was interpreted as evidence for a domain-general inhibitory mechanism (RIF) underlying first language attrition. Because this result is at odds with some previous findings and theoretical assumptions, we wanted…

How Does High Impact Practice Predict Student Engagement? A Comparison of White and Minority Students

ERIC Educational Resources Information Center

Sweat, Jeffrey; Jones, Glenda; Han, Suejung; Wolfgram, Susan M.

2013-01-01

This High Impact Practices (HIPS) contribute to higher retention and graduation rates. HIPS are effective for racial and ethnic minorities in particular, who disproportionately experience high and persistent levels of postsecondary attrition. Little is known about the mechanism by which HIPS promote retention. Based on a random survey of 268…

Teacher Effects on Student Attrition and Performance in Mass-Market Tertiary Education

ERIC Educational Resources Information Center

Foster, Gigi

2010-01-01

Tertiary education is now accessible even to those who appear unlikely "ex ante" to succeed in jobs requiring post-high school education. Institutions that have broadened access to their programs must rely on two things to protect the quality of the degrees they award: selection mechanisms operating during students' tenure, and effective…

Attrition and Retention.

ERIC Educational Resources Information Center

Brasher, Daniel E.; And Others

Trends in beginning freshmen attrition were studied at the University of Tennessee, Martin, for the fall quarters of 1977, 1978, and 1979. One part of the attrition study used the American College Testing (ACT) program's withdrawing/nonreturning student survey, while a second approach was based on the computerized People Oriented Information…

Waivered Recruits: An Evaluation of Their Performance and Attrition Risk

DTIC Science & Technology

2011-03-01

III recruit. Figure 12. Marginal effects of waivers on 6-, 24-, and 48-month attrition rates: Navya Adult Felony Juvenile Felony Serious...efforts. Table 9. Characteristics that are correlated, on average, with a lower attrition risk (for the waiver types considered) Army Navya Marine

Structural and spectroscopic study of mechanically synthesized SnO2 nanostructures

NASA Astrophysics Data System (ADS)

Vij, Ankush; Kumar, Ravi

2016-05-01

We report the single step synthesis of SnO2 nanostructures using high energy mechanical attrition method. X-ray diffraction (XRD) pattern reveals the single phase rutile structure with appreciable broadening of diffraction peaks, which is a signature of nanostructure formation. The average crystallite size of SnO2 nanostructures has been calculated to be ~15 nm. The micro-Raman study reveals the shifting of A1g Raman mode towards lower wave number, which is correlated with the nanostructure formation.

Knowing the "Right Stuff": Attrition, Gender, and Scientific Literacy.

ERIC Educational Resources Information Center

McDade, Laurie A.

1988-01-01

For undergraduate women, attrition from chemistry and mathematics disciplines because of their noncompetitive performance involves abandoning their original goals. Male students explain their attrition as pragmatic moves toward more rewarding fields and do not, unlike women, question their talents as "math wiz kids." Reasons for this difference…

Student Attrition: Strategies for Action.

ERIC Educational Resources Information Center

Alfred, Richard L., Ed.

Four main objectives of the conference reported in these proceedings were: (1) to provide a basic orientation for two-year college faculty and administrative personnel as to what student attrition is and the types of impact that it has upon the institutional setting; (2) to interpret the vocabulary pertinent to student attrition, identifying new…

Leaving College: Rethinking the Causes and Cures of Student Attrition.

ERIC Educational Resources Information Center

Tinto, Vincent

The dimensions and consequences of college student attrition and features of institutional action to deal with attrition are discussed. Patterns of student departure from individual colleges as opposed to permanent college withdrawal are addressed. After synthesizing the research on multiple causes of student leaving, a theory of student departure…

Attrition from an Adolescent Addiction Treatment Program: A Cross Validation.

ERIC Educational Resources Information Center

Mathisen, Kenneth S.; Meyers, Kathleen

Treatment attrition is a major problem for programs treating adolescent substance abusers. To isolate and cross validate factors which are predictive of addiction treatment attrition among adolescent substance abusers, screening interview and diagnostic variables from 119 adolescent in-patients were submitted to a discriminant equation analysis.…

Who Will Stay and Who Will Leave? Predicting Secondary English Teacher Attrition Risk

ERIC Educational Resources Information Center

Hancock, Carl B.; Scherff, Lisa

2010-01-01

Although there are considerable large-scale data on teacher attrition, few researchers have culled information specifically related to English teachers' risk for attrition. This study examines the effects of teacher characteristics, teaching conditions, student variables, self-efficacy, external support, and salary on secondary English language…

Stemming the Revolving Door: Teacher Retention and Attrition in Arctic Alaska Schools

ERIC Educational Resources Information Center

Kaden, Ute; Patterson, Philip P.; Healy, Joanne; Adams, Barbara L.

2016-01-01

Limited research is available concerning teacher retention and teacher attrition in Arctic Alaska. This paper reports survey research findings, which identify factors related to teacher retention and attrition in Alaskan Arctic Native communities. Teacher retention rates (2009-2013) vary widely over time showing no significant trends. Results…

Choosing and Leaving Science in Highly Selective Institutions.

ERIC Educational Resources Information Center

Strenta, A. Christopher; And Others

1994-01-01

A study investigated causes of initial interest in and attrition from natural sciences and engineering among 5,320 students entering 4 highly selective institutions in 1988, with attention to probable causes of disproportionate attrition of women. Reasons for high attrition were based on cognitive variables or the perceived "chilly"…

Irreconcilable Differences: Teacher Attrition in Public and Catholic Schools

ERIC Educational Resources Information Center

Scheopner, Aubrey J.

2010-01-01

Teachers have a powerful impact on student achievement, yet high attrition rates hinder the ability of schools to provide quality instruction. Attrition rates are highest for schools serving low income, minority students and among small private schools. This review of research seeks to understand why teachers leave, examining different teaching…

The Problem of Student Attrition in Higher Education: An Alternative Perspective

ERIC Educational Resources Information Center

Beer, Colin; Lawson, Celeste

2017-01-01

Student attrition continues to be a significant and costly challenge for higher education institutions across the globe. In Australia, universities cite the importance of addressing student attrition through strategic statements and policy documents, and expend time and resources on the problem. Despite vast expenditures, they have made little…

Minimizing Attrition in Online Degree Courses

ERIC Educational Resources Information Center

Boton, Eliani Colferai; Gregory, Sue

2015-01-01

The number of online programs in the higher education sector has increased dramatically in the last decade, and with it, an increase in attrition has become a recurring problem worldwide. Literature suggests that elements of culture, motivation, learning management systems and online pedagogy play a major role in attrition rates in the higher…

Early Career Teacher Attrition: Intentions of Teachers Beginning

ERIC Educational Resources Information Center

Clandinin, D. Jean; Long, Julie; Schaefer, Lee; Downey, C. Aiden; Steeves, Pam; Pinnegar, Eliza; McKenzie Robblee, Sue; Wnuk, Sheri

2015-01-01

Early career teacher attrition has most often been conceptualized as either a problem associated with individual factors (e.g. burnout) or a problem associated with contextual factors (e.g. support and salary). This study considered early career teacher attrition as an identity making process that involves a complex negotiation between individual…

Early Attrition among Suicidal Clients

ERIC Educational Resources Information Center

Surgenor, P. W. G.; Meehan, V.; Moore, A.

2016-01-01

The study aimed to identify the level of suicidal ideation in early attrition clients and their reasons for the early termination of their therapy. The cross-sectional design involved early attrition clients (C[subscript A]) who withdrew from therapy before their second session (n = 61), and continuing clients who (C[subscript C]) progressed…

A critique of age estimation using attrition as the sole indicator.

PubMed

Ball, J

2002-12-01

The age determination of skeletal remains has been carried out using anthropological examination of the remaining bones and dentition. The aging of the dentition is based on attrition which, if physiological will correlate with age. Occasionally the only material available is a single tooth or a few teeth, or in the case of a living person, teeth in situ. In certain cases microscopic examination of the teeth may not be possible and the age estimation is then often determined by the degree of attrition associated with the tooth. In more recent times the causes of attrition have involved other factors such as bruxism, diet, environment and medication. The weaknesses and limitations of age estimation by examination of dental attrition as the sole indicator of age are highlighted.

Attrition during graduate medical education: medical school perspective.

PubMed

Andriole, Dorothy A; Jeffe, Donna B; Hageman, Heather L; Klingensmith, Mary E; McAlister, Rebecca P; Whelan, Alison J

2008-12-01

To identify predictors of attrition during graduate medical education (GME) in a single medical school cohort of contemporary US medical school graduates. Retrospective cohort study. Single medical institution. Recent US allopathic medical school graduates. Attrition from initial GME program. Forty-seven of 795 graduates (6%) did not complete the GME in their initial specialty of choice. At bivariate analysis, attrition was associated with election to the Alpha Omega Alpha Honor Medical Society, being an MD-PhD degree holder, and specialty choice (all P < .05). Attrition was not associated with graduation year (P = .91), sex (P = .67), or age (P = .12). In a multivariate logistic regression model, MD-PhD degree holder (odds ratio, 3.43; 95% confidence interval, 1.27-9.26; P = .02), election to Alpha Omega Alpha (2.19; 1.04-4.66; P = .04), choice of general surgery for GME (5.32; 1.98-14.27; P < .001), and choice of 5-year surgical specialty including those surgical specialties with a GME training requirement of 5 years or longer (2.74; 1.16-6.44; P = .02) each independently predicted greater likelihood of attrition. Academically highly qualified graduates and graduates who chose training in general surgery or in a 5-year surgical specialty were at increased risk of attrition during GME.

Reaction bonded silicon nitride prepared from wet attrition-milled silicon. [fractography

NASA Technical Reports Server (NTRS)

Herball, T. P.; Glasgow, T. K.; Shaw, N. J.

1980-01-01

Silicon powder wet milled in heptane was dried, compacted into test bar shape, helium-sintered, and then reaction bonded in nitrogen-4 volume percent hydrogen. As-nitrided bend strengths averaged approximately 290 MPa at both room temperature and 1400 C. Fracture initiation appeared to be associated with subsurface flaws in high strength specimens and both subsurface and surface flaws in low strength specimens.

Reaction bonded silicon nitride prepared from wet attrition-milled silicon

NASA Technical Reports Server (NTRS)

Herbell, T. P.; Glasgow, T. K.; Shaw, N. J.

1980-01-01

Silicon powder wet milled in heptane was dried, compacted into test bar shape, helium-sintered, and then reaction bonded in nitrogen-4 vol% hydrogen. As-nitrided bend strengths averaged approximately 290 MPa at both room temperature and 1400 C. Fracture initiation appeared to be associated with subsurface flaws in high-strength specimens and both subsurface and surface flaws in low-strength specimens.

Effect of the powder characteristics of Sisub3Nsub4 on the microstructure of sintered bodies

NASA Technical Reports Server (NTRS)

Woetting, G.; Hausner, H.

1981-01-01

Silicon nitride powders sintered with the addition of 2 wt% Mg0 to 95% theoretical density after attrition milling and subsequent purification were evaluated. Preparation of the powders is described. The powder characteristics (specific surfaces, iron concentration, and oxygen content), and density, weight loss, and phase state of the sinter bodies as a function of powder preparation are presented.

Attrition from antiretroviral treatment services among pregnant and non-pregnant patients following adoption of Option B+ in Haiti

PubMed Central

Domercant, Jean Wysler; Puttkammer, Nancy; Young, Paul; Yuhas, Krista; François, Kesner; Grand’Pierre, Reynold; Lowrance, David; Adler, Michelle

2017-01-01

ABSTRACT Background: Access to antiretroviral therapy (ART) has expanded in Haiti because of the adoption of Option B+ and the revision of treatment guidelines. Retention in care and treatment varies greatly and few studies have examined retention rates, particularly among women enrolled in Option B+. Objective: To assess attrition among pregnant and non-pregnant patients initiating ART following adoption of Option B+ in Haiti. Methods: Longitudinal data of adult patients initiated on ART from October 2012 through August 2014 at 73 health facilities across Haiti were analyzed using a survival analysis framework to determine levels of attrition. The Kaplan–Meier method and Cox proportional hazards regression were used to examine risk factors associated with attrition. Results: Among 17,059 patients who initiated ART, 7627 (44.7%) were non-pregnant women, 5899 (34.6%) were men, and 3533 (20.7%) were Option B+ clients. Attrition from the ART program was 36.7% at 12 months (95% CI: 35.9–37.5%). Option B+ patients had the highest level of attrition at 50.4% at 12 months (95% CI: 48.6–52.3%). While early HIV disease stage at ART initiation was protective among non-pregnant women and men, it was a strong risk factor among Option B+ clients. In adjusted analyses, key protective factors were older age (p < 0.0001), living near the health facility (p = 0.04), having another known HIV-positive household member (p < 0.0001), having greater body mass index (BMI) (p < 0.0001), pre-ART counseling (p < 0.0001), and Cotrimoxazole prophylaxis during baseline (p < 0.01). Higher attrition was associated with rapidly starting ART after enrollment (p < 0.0001), anemia (p < 0.0001), and regimen tenofovir+lamivudine+nevirapine (TDF+3TC+NVP) (p < 0.001). Conclusions: ART attrition in Haiti is high among adults, especially among Option B+ patients. Identifying newly initiated patients most at risk for attrition and providing appropriate interventions could help reduce ART attrition. PMID:28640661

Examining attrition rates at one specialty addiction treatment provider in the United States: a case study using a retrospective chart review.

PubMed

Loveland, David; Driscoll, Hilary

2014-09-25

Engaging individuals who have a substance use disorder (SUD) in treatment continues to be a challenge for the specialty addiction treatment field. Research has consistently revealed high rates of missed appointments at each step of the enrollment process: 1. between calling for services and assessment, 2. between assessment and enrollment, and 3. between enrollment and completion of treatment. Extensive research has examined each step of the process; however, there is limited research examining the overall attrition rate across all steps. A single case study of a specialty addiction treatment agency was used to examine the attrition rates across the first three steps of the enrollment process. Attrition rates were tracked between August 1, 2011 and July 31, 2012. The cohort included 1822 unique individuals who made an initial request for addiction treatment services. Monthly retrospective reviews of medical records, phone logs, and billing data were used to calculate attrition rates. Attrition rates reported in the literature were collected and compared to the rates found at the target agency. Median time between request for treatment and assessment was 6 days (mean 7.5) and between assessment and treatment enrollment was 8 days (mean 12.5). An overall attrition rate of 80% was observed, including 45% between call and assessment, 32% between assessment and treatment enrollment (another 17% could not be determined), and 37% left or were removed from treatment before 30 days. Women were less likely to complete 30 days of treatment compared to men. No other demographics were related to attrition rates. One out of every five people who requested treatment completed a minimum of 30 days of a treatment. The attrition rate was high, yet similar to rates noted in the literature. Limitations of the single case study are noted. Attrition rates in the U.S. are high with approximately 75% to 80% of treatment seekers disengaging at one of the multiple stages of the enrollment and treatment process. Significant changes in the system are needed to improve engagement rates.

Attrition, occlusion, (dys)function, and intervention: a systematic review.

PubMed

van 't Spijker, Arie; Kreulen, Cees M; Creugers, Nico H J

2007-06-01

Attrition and occlusal factors and masticatory function or dysfunction are thought to be related. This study aims to systematically review the literature on this topic with the emphasis to find evidence for occlusion-based treatment protocols for attrition. Literature was searched using PubMed (1980 to 2/2006) and the Cochrane Library of Clinical Trials with the keywords 'tooth' and 'wear'. Five steps were followed. Exclusion was based on the following: (1) reviews, case-reports, studies on non-human tooth material, and studies not published in English and (2) historical or forensic studies. Included were (3) in vivo studies. Next, studies on (4) occlusal factors, function or dysfunction [temporomandibular disorders (TMD), bruxism], or intervention, and (5) attrition were included. Two investigators independently assessed the abstracts; measure of agreement was calculated using Cohen's kappa; disagreement was resolved by discussion. Full-text articles were obtained and correlation between outcomes on occlusal factors, (dys)function, treatment, and attrition were retrieved. References in the papers included in the final analysis were cross-matched with the original list of references to add references that met the inclusion criteria. The search procedure revealed 1289 references on tooth wear. The numbers of included studies after each step were (1) 345 (kappa=0.8), (2) 287 (kappa=0.87), (3) 174 (kappa=0.99), (4) 81 (kappa=0.71), and (5) 27 (kappa=0.68). Hand searches through the reference lists revealed six additional papers to be included. Analysis of the 33 included papers failed to find sound evidence for recommending a certain occlusion-based treatment protocol above another in the management of attrition. Some studies reported correlations between attrition and anterior spatial relationships. No studies were found suggesting that absent posterior support necessarily leads to increased attrition, though one study found that fewer number of teeth resulted in higher tooth wear index (on the remaining teeth). Attrition seems to be co-existent with self-reported bruxism. Reports on attrition and TMD signs and symptoms provide little understanding of the relationship between the two.

Attrition from antiretroviral treatment services among pregnant and non-pregnant patients following adoption of Option B+ in Haiti.

PubMed

Domercant, Jean Wysler; Puttkammer, Nancy; Young, Paul; Yuhas, Krista; François, Kesner; Grand'Pierre, Reynold; Lowrance, David; Adler, Michelle

2017-01-01

Access to antiretroviral therapy (ART) has expanded in Haiti because of the adoption of Option B+ and the revision of treatment guidelines. Retention in care and treatment varies greatly and few studies have examined retention rates, particularly among women enrolled in Option B+. To assess attrition among pregnant and non-pregnant patients initiating ART following adoption of Option B+ in Haiti. Longitudinal data of adult patients initiated on ART from October 2012 through August 2014 at 73 health facilities across Haiti were analyzed using a survival analysis framework to determine levels of attrition. The Kaplan-Meier method and Cox proportional hazards regression were used to examine risk factors associated with attrition. Among 17,059 patients who initiated ART, 7627 (44.7%) were non-pregnant women, 5899 (34.6%) were men, and 3533 (20.7%) were Option B+ clients. Attrition from the ART program was 36.7% at 12 months (95% CI: 35.9-37.5%). Option B+ patients had the highest level of attrition at 50.4% at 12 months (95% CI: 48.6-52.3%). While early HIV disease stage at ART initiation was protective among non-pregnant women and men, it was a strong risk factor among Option B+ clients. In adjusted analyses, key protective factors were older age (p < 0.0001), living near the health facility (p = 0.04), having another known HIV-positive household member (p < 0.0001), having greater body mass index (BMI) (p < 0.0001), pre-ART counseling (p < 0.0001), and Cotrimoxazole prophylaxis during baseline (p < 0.01). Higher attrition was associated with rapidly starting ART after enrollment (p < 0.0001), anemia (p < 0.0001), and regimen tenofovir+lamivudine+nevirapine (TDF+3TC+NVP) (p < 0.001). ART attrition in Haiti is high among adults, especially among Option B+ patients. Identifying newly initiated patients most at risk for attrition and providing appropriate interventions could help reduce ART attrition.

A meta-analysis of predictors of offender treatment attrition and its relationship to recidivism.

PubMed

Olver, Mark E; Stockdale, Keira C; Wormith, J Stephen

2011-02-01

The failure of offenders to complete psychological treatment can pose significant concerns, including increased risk for recidivism. Although a large literature identifying predictors of offender treatment attrition has accumulated, there has yet to be a comprehensive quantitative review. A meta-analysis of the offender treatment literature was conducted to identify predictors of offender treatment attrition and examine its relationship to recidivism. The review covered 114 studies representing 41,438 offenders. Sex offender and domestic violence programs were also examined separately given their large independent literatures. The overall attrition rate was 27.1% across all programs (k = 96), 27.6% from sex offender programs (k = 34), and 37.8% from domestic violence programs (k = 35). Rates increased when preprogram attrition was considered. Significant predictors included demographic characteristics (e.g., age, rw = -.10), criminal history and personality variables (e.g., prior offenses, rw = .14; antisocial personality, rw = .14), psychological concerns (e.g., intelligence, rw = -.14), risk assessment measures (e.g., Statistical Information on Recidivism scale, rw =.18), and treatment-related attitudes and behaviors (e.g., motivation, rw = -.13). Results indicated that treatment noncompleters were higher risk offenders and attrition from all programs significantly predicted several recidivism outcomes ranging from rw = .08 to .23. The clients who stand to benefit the most from treatment (i.e., high-risk, high-needs) are the least likely to complete it. Offender treatment attrition can be managed and clients can be retained through an awareness of, and attention to, key predictors of attrition and adherence to responsivity considerations.

The interactions between attrition, abrasion and erosion in tooth wear.

PubMed

Shellis, R Peter; Addy, Martin

2014-01-01

Tooth wear is the result of three processes: abrasion (wear produced by interaction between teeth and other materials), attrition (wear through tooth-tooth contact) and erosion (dissolution of hard tissue by acidic substances). A further process (abfraction) might potentiate wear by abrasion and/or erosion. Knowledge of these tooth wear processes and their interactions is reviewed. Both clinical and experimental observations show that individual wear mechanisms rarely act alone but interact with each other. The most important interaction is the potentiation of abrasion by erosive damage to the dental hard tissues. This interaction seems to be the major factor in occlusal and cervical wear. The available evidence is insufficient to establish whether abfraction is an important contributor to tooth wear in vivo. Saliva can modulate erosive/abrasive tooth wear, especially through formation of pellicle, but cannot prevent it. © 2014 S. Karger AG, Basel.

Impact of a Spiral Organic Curriculum on Student Attrition and Learning

ERIC Educational Resources Information Center

Grove, Nathaniel P.; Hershberger, James W.; Bretz, Stacey Lowery

2008-01-01

At Miami University, the attrition rate in the year-long organic chemistry sequence for pre-medical majors typically ranges from 30-50%. To decrease attrition, the Department of Chemistry and Biochemistry developed an innovative, spiral curriculum. Unlike a traditional organic chemistry course that moves sequentially through the material, the…

The Regression Hypothesis as a Framework for First Language Attrition

ERIC Educational Resources Information Center

Keijzer, Merel

2010-01-01

In an attempt to explain first language attrition in emigrant populations, this paper investigates the explanatory power of a framework that has--until now--received little attention: the regression hypothesis (Jakobson, 1941). This hypothesis predicts that the order of attrition is the reverse of the order of acquisition. The regression…

From Departure to Arrival: Re-Engaging Students Who Have Withdrawn from University

ERIC Educational Resources Information Center

Harvey, Andrew; Szalkowicz, Giovanna

2017-01-01

Despite institutional strategies to prevent student withdrawal, attrition remains a concern across higher education sectors in the United States, the United Kingdom and Australia. In the case of Australian universities, attrition rates have remained consistently high since 2002. Some level of attrition is inevitable, but universities can influence…

Penetrating a Wall of Introspection: A Critical Attrition Analysis

ERIC Educational Resources Information Center

Johannsen, Bjorn Friis; Rump, Camilla Osterberg; Linder, Cedric

2013-01-01

This paper presents a critical analysis of student discourse on attrition as it unfolds in interviews on early departure from higher education. A synthesis of relevant studies and modelling done in the field shows that essential aspects affecting attrition and retention can be effectively conceptualized and acted upon in terms of the interplay…

Disfluency Markers in L1 Attrition

ERIC Educational Resources Information Center

Schmid, Monika S.; Fagersten, Kristy Beers

2010-01-01

Based on an analysis of the speech of long-term emigres of German and Dutch origin, the present investigation discusses to what extent hesitation patterns in language attrition may be the result of the creation of an interlanguage system, on the one hand, or of language-internal attrition patterns on the other. We compare speech samples elicited…

Academic Momentum and Undergraduate Student Attrition: Comparative Analysis in US and Russian Universities

ERIC Educational Resources Information Center

Kondratjeva, Olga; Gorbunova, Elena V.; Hawley, Joshua D.

2017-01-01

Student attrition in postsecondary education is a significant public policy problem. Nations invest substantial resources in college systems, and when students leave, this investment is lost. To understand the factors that influence student attrition in US and Russian public universities, we use the perspective of academic momentum, defined…

Retention and Attrition in a Home Visiting Programme: Looking Back and Moving Forward

ERIC Educational Resources Information Center

Fifolt, Matthew; Lanzi, Robin G.; Johns, Elisabeth; Strichik, Tracye; Preskitt, Julie

2017-01-01

Objective: The purpose of this study was to investigate retention and attrition in First Teacher, Alabama's Maternal, Infant, and Early Childhood Home Visiting (MIECHV) programme. Methods: Secondary data analysis was used to identify families that were most likely to leave through attrition; focus groups were conducted to discuss potential reasons…

Agency, Socialization, and Support: A Critical Review of Doctoral Student Attrition

ERIC Educational Resources Information Center

Rigler, Kenneth L., Jr.; Bowlin, Linda K.; Sweat, Karen; Watts, Stephen; Throne, Robin

2017-01-01

Almost universally, residential doctoral programs have reported attrition rates of up to 50% for face-to-face programs and 50-70% for online doctoral programs. The purpose of this critical review was to explore current literature for doctoral attrition and persistence to explore reasons and attributes for improved persistence to completion. We…

A Comparative Study of Administrator and Special Education Teacher Perceptions of Special Education Teacher Attrition and Retention

ERIC Educational Resources Information Center

Sheldrake, Danielle Angelina

2013-01-01

This mixed methods study identifies perceived causes of and solutions to the attrition of special education teachers. Researchers have documented that special education teaching positions encounter higher attrition rates than their general education peers (Katsiyannis, Zhang, & Conroy in Olivarez & Arnold, 2006; Mitchell & Arnold,…

Completion and Attrition Rates for Apprentices and Trainees, 2016. Australian Vocational Education and Training Statistics

ERIC Educational Resources Information Center

National Centre for Vocational Education Research (NCVER), 2017

2017-01-01

This publication presents completion and attrition rates for apprentices and trainees using three different methodologies: (1) contract completion and attrition rates: based on the outcomes of contracts of training; (2) individual completion rates: based on contract completion rates and adjusted for factors representing average recommencements by…

Measuring (and Managing) the Invisible Costs of Postsecondary Attrition. Policy Brief

ERIC Educational Resources Information Center

Wellman, Jane; Johnson, Nate; Steele, Patricia

2012-01-01

The collision between funding realities and the paramount goal of increasing educational attainment has brought new attention to ways to reduce postsecondary attrition and get more students who enroll in college to complete a degree or credential. Reductions in attrition are both educationally effective and cost effective. Students reach…

Exploring Differential Attrition Rates among System of Care Evaluation Participants

ERIC Educational Resources Information Center

Rogers, Kelly N.; Fernandez, Maria; Thurber, Lori; Smitley, Andy

2004-01-01

The purpose of the present study is to investigate differential attrition rates in terms of both demographic characteristics and initial levels of child functioning of participants in North Carolina's system of care evaluation. Participants included 303 families (78 dropped out of the study, a 26% attrition rate). Families dropped out of the…

The Case for Increasing Workplace Decision-Making: Proposing a Model for Special Educator Attrition Research

ERIC Educational Resources Information Center

Tyler, Teresa A.; Brunner, C. Cryss

2014-01-01

The chronically high rate of special educator attrition across U.S. schools creates a dilemma for educational leaders because special educators provide direct services to students with special needs. Attrition exacerbates already high special educator shortages reported in most districts, and nearly one million schoolchildren with disabilities…

Analyzing the Findings of the Saudi Research on Student Attrition in Higher Education

ERIC Educational Resources Information Center

Aljohani, Othman

2016-01-01

This paper presents a comprehensive review of the available literature on student attrition in Saudi higher education context. Despite the reported low student retention rates in Saudi tertiary institutions, student attrition remains an under-researched phenomenon. Thus, this paper aims to trace and collect all the available studies that addressed…

Attrition Standard. WWC Standards Brief

ERIC Educational Resources Information Center

What Works Clearinghouse, 2017

2017-01-01

"Attrition" is the loss of sample during the course of a study. It occurs when individuals initially randomly assigned in a study are not included when researchers examine the outcome of interest. Attrition is a common issue in education research, and it occurs for many reasons. The What Works Clearinghouse (WWC) is an initiative of the…

Completion and Attrition Rates for Apprentices and Trainees 2014. Australian Vocational Education and Training Statistics

ERIC Educational Resources Information Center

National Centre for Vocational Education Research (NCVER), 2015

2015-01-01

This publication presents completion and attrition rates for apprentices and trainees using three different methodologies: (1) contract completion and attrition rates: based on the outcomes of contracts of training; (2) individual completion rates: based on contract completion rates and adjusted for factors representing average recommencements by…

The Impact of Attrition on Vocabulary Knowledge among Saudi Teachers

ERIC Educational Resources Information Center

Alharthi, Thamer

2014-01-01

This two-year longitudinal study tracks the extent of vocabulary attrition among Arabic-speaking English graduate teachers. Data were collected through pre-post tests of receptive and productive vocabulary knowledge. The results showed drastic attrition in vocabulary knowledge soon after the end of formal instruction followed by slight gain,…

Obstacles to Success--Doctoral Student Attrition in South Africa

ERIC Educational Resources Information Center

Herman, Chaya

2011-01-01

The article explores doctoral attrition in South Africa, investigating and comparing the attributions of attrition of doctoral students and PhD programme leaders. The article is based on secondary data analysis of two large studies on doctoral education in South Africa. The main point of the article is that the different understandings of the…

Texas Public School Attrition Study, 2011-12. IDRA Report

ERIC Educational Resources Information Center

Johnson, Roy L.; Montes, Felix

2012-01-01

This document contains 3 statistical reports. The first report, "Attrition Rate Decline Seems Promising--Though High Schools are Still Losing One in Four Students" (by Roy L. Johnson), presents results of long-term trend assessments of attrition data in Texas public high schools. The second report, "Slow Declining Pace Keeps Zero…

Attrition resistant Fischer-Tropsch catalyst and support

DOEpatents

Singleton, Alan H.; Oukaci, Rachid; Goodwin, James G.

2004-05-25

A catalyst support having improved attrition resistance and a catalyst produced therefrom. The catalyst support is produced by a method comprising the step of treating calcined .gamma.-alumina having no catalytic material added thereto with an acidic aqueous solution having an acidity level effective for increasing the attrition resistance of the calcined .gamma.-alumina.

Use of aptitude to understand bachelor of science in nursing student attrition and readiness for the National Council Licensure Examination-Registered Nurse.

PubMed

Newton, Sarah E; Moore, Gary

2009-01-01

Attrition is a serious issue among Bachelor of Science in Nursing (BSN) students with attrition rates around 50% nationwide. To help minimize BSN student attrition, many nursing programs use commercially available standardized nursing aptitude tests as adjuncts to scholastic aptitude data, usually operationalized as pre-nursing grade point average, to select students for admission. Little is known regarding the usefulness of scholastic and nursing aptitude data for predicting long-term retention in a BSN program and readiness for the National Council Licensure Examination-Registered Nurse (NCLEX-RN). Therefore, the purpose of this study was to describe the relationships among scholastic aptitude, nursing aptitude, BSN student attrition prior to the final semester of the curriculum, and BSN student readiness for the NCLEX-RN. This study's findings, along with other findings in the literature, suggest the need for a parsimonious explanatory model of BSN student attrition that can be used to guide admission and progression policies, and ensure that students ready for the NCLEX-RN are the ones graduating from BSN programs.

Attitudes towards attrition among UK trainees in obstetrics and gynaecology.

PubMed

Gafson, Irene; Currie, Jane; O'Dwyer, Sabrina; Woolf, Katherine; Griffin, Ann

2017-06-02

Physician dissatisfaction in the workplace has consequences for patient safety. Currently in the UK, 1 in 5 doctors who enter specialist training in obstetrics and gynaecology leave the programme before completion. Trainee attrition has implications for workforce planning, organization of health-care services and patient care. The authors conducted a survey of current trainees' and former trainees' views concerning attrition and 'peri-attrition' - a term coined to describe the trainee who has seriously considered leaving the specialty. The authors identified six key themes which describe trainees' feelings about attrition in obstetrics and gynaecology: morale and undermining; training processes and paperwork; support and supervision; work-life balance and realities of life; NHS environment; and job satisfaction. This article discusses themes of an under-resourced health service, bullying, lack of work-life balance and poor personal support.

Adherence and Attrition in a Web-Based Lifestyle Intervention for People with Metabolic Syndrome

PubMed Central

JAHANGIRY, Leila; SHOJAEIZADEH, Davoud; MONTAZERI, Ali; NAJAFI, Mahdi; MOHAMMAD, Kazem; YASERI, Mehdi

2014-01-01

Abstract Background The aim of this study was to determine adherence and attrition rates in a lifestyle intervention for people with metabolic syndrome. Methods Adherence and attrition data from a randomized controlled trial were collected. Participants were classified as adherence group if they completed assessments at 3 and 6 months follow-up and as attrition group if they did not. Physical activity and quality of life was measured using the International Physical Activity Questionnaire (IPAQ) and the Short Form Health Survey (SF-36). Generalized Estimating Equations (GEE) was used to explore predictors of attrition. Results The mean age of participants (n=160) was 44.1 years. Attrition rate in the intervention and control groups at first follow-up were the same (20%). However, the control group had significantly higher attrition rate (%33.7) compared to the intervention group (%20) at 6 months follow up. Results showed that low educated participants were more likely to not stay in the study than better educated participants (OR=2.95,CI:1.39-6.33,P=0.05). According with length of the study, attrition was decreased at six month (OR=0.66,CI:0.52-0.83,P<0.001). Also, some aspects of health-related quality of life contributed to the attrition rate. Those who had higher scores on general health (OR=0.66,CI:0.54-0.97,P=0.023), social functioning (OR=0.44,CI:0.40-0.76,P=0.032), role emotional (OR=0.74,CI:0.54-0.98,P=0.18), vitality (OR=0.55,CI:0.38-0.90,P=0.015) and mental health (OR=0.63,CI:0.45-0.85,P=0.033) were more likely to stay in the study. Conclusion It remains a concern that Web-based lifestyle programs may fail to reach those who need it most. Participant in the study generally had better quality of life than those who were lost to follow up. PMID:26175979

Issues concerning recruitment, retention and attrition of student nurses in the 1950/60s: a comparative study.

PubMed

Jinks, Annette M; Richardson, Kathleen; Jones, Chris; Kirton, Jennifer A

2014-11-01

To investigate student nurse recruitment and attrition in the 1950' and 1960s and undertake comparisons to modern day concerns. The study was set in one hospital in the U.K. In the period studied nursing was unpopular as a profession and there were difficulties surrounding recruitment. Attrition rates were high. Documentary analysis of 641 training records dating 1955 to 1968 was undertaken. Attrition rates, reasons for non-completion and employment following successful completion were determined. Most recruits were young, unmarried, females and had overseas addresses. The majority (n = 88) had prior nursing experience. Over 69% (n = 443) successfully completed their training. Attrition rates were over 30% (n = 198), the main reason being academic failure. Following completion over 40% (n = 183) undertook midwifery training (n = 183) or secured a staff nurse post (n = 153). Issues relating to recruitment, retention and attrition in the 1950s and 1960s put into context present day issues. Recent attrition rates from pre-registration nurse education have fallen, nevertheless some of the issues of yesteryear remain problematic. In the present study significant numbers of entrants left due to domestic and ill-health problems resonates with many modern day studies. Also failure to complete due to academic shortcomings continues to be a concern. Copyright © 2014 Elsevier Ltd. All rights reserved.

Learning and Study Strategies of Baccalaureate Nursing Students during First Semester Nursing Courses

ERIC Educational Resources Information Center

Gatto, Susan L.

2010-01-01

Background. Attrition rates from nursing courses and programs are reported to range from 3 to 55 percent with 20 to 80 percent due to involuntary attrition (academic failure). While trying to address the nursing shortage, nursing programs increased enrollment, but did not produce enough graduates since involuntary attrition also increased. While…

Spiritual Practices as a Means of Coping with and Ameliorating Stress to Reduce Teacher Attrition

ERIC Educational Resources Information Center

Hartwick, James M. M.; Kang, Shin Ji

2013-01-01

Teacher attrition has been a serious problem in maintaining quality education in the United States. Although the research produced extensive documentation on teachers' stress and attrition, little attention has been paid to their spiritual stress coping strategies. This article documents various spiritual practices as a means of coping with…

Differential Effects of Language Attrition in the Domains of Verb Placement and Object Expression

ERIC Educational Resources Information Center

Flores, Cristina

2012-01-01

This study investigates the differential effects of language attrition in two diverse linguistic domains: verb placement and object expression. Linguistic phenomena at the syntax--discourse interface, such as object expression, have been shown to be more vulnerable to attrition than narrow syntax properties, such as verb placement. This study aims…

An Event History Analysis of Teacher Attrition: Salary, Teacher Tracking, and Socially Disadvantaged Schools

ERIC Educational Resources Information Center

Kelly, Sean

2004-01-01

In this event history analysis of the 1990-1991 Schools and Staffing Survey and the 1992 Teacher Follow-up Survey, a retrospective person-year database was constructed to examine teacher attrition over the course of the teaching career. Consistent with prior research, higher teacher salaries reduced attrition, but only slightly so. Teacher…

Attrition in the Trades. Research Overview. Monograph Series 07/2011

ERIC Educational Resources Information Center

Wilson, Sara

2011-01-01

"Attrition in the trades," by Tom Karmel, Patrick Lim and Josie Misko, analyses whether attrition--the gradual reduction or weakening of a workforce--occurs more amongst tradespeople than professionals, and if this is to the detriment of the supply of tradespeople. The authors use data from the Australian Labour Mobility Survey in 2008…

Characterization of Nanocrystalline Aluminum Alloy 5083 Powders Produced by Cryogenic Attrition

DTIC Science & Technology

2014-11-01

Characterization of Nanocrystalline Aluminum Alloy 5083 Powders Produced by Cryogenic Attrition by Tiffany Ngo ARL-TN-0643...November 2014 Characterization of Nanocrystalline Aluminum Alloy 5083 Powders Produced by Cryogenic Attrition Tiffany Ngo Weapons and...3. DATES COVERED (From - To) August 2014 4. TITLE AND SUBTITLE Characterization of Nanocrystalline Aluminum Alloy 5083 Powders Produced by

Assessing the Impact of Faculty-Led Supplemental Instruction on Attrition, GPA, and Graduation Rates

ERIC Educational Resources Information Center

Bryan, Karla Needham

2013-01-01

The purpose of this quasi-experimental, quantitative study was to investigate the effectiveness of supplemental instruction (SI) as a means to address the existing high attrition and low graduation rates evidenced at a rural southern community college. The research problem addressed the high attrition rates in barrier courses and low graduation…

First-Term Attrition among Marine Corps Women: Some Associated Factors.

ERIC Educational Resources Information Center

Royle, Marjorie H.

Because the first-term attrition rate for enlisted Marine Corps women is nearly 50 percent, or about twice that for comparable men, a study was undertaken to identify factors that might be related to this high attrition rate. During the study, the following three data sets were analyzed: historical master files and recruit accession management…

Analysis of Students Attrition in the Sciences Subjects Areas in Ambrose Alli University, Ekpoma

ERIC Educational Resources Information Center

Olusi, F. I.; Akahomen, D. O.; Otete, C. O.

2013-01-01

The study, analysis of student's attrition in Ambrose Alli University (AAU) Ekpoma Nigeria was carried out to determine the exact number of students who attrite from selected faculties of the university. The study employed the descriptive survey design. Three hypotheses were stated and tested. On the hypothesis which tested the general attrition…

Preliminary Development of an Attrition Risk Assessment Instrument for Secondary Agricultural Educators

ERIC Educational Resources Information Center

Greenhaw, Laura L.; Brashears, M. Todd; Burris, Scott; Meyers, Courtney; Morrison, Carley C.

2017-01-01

Secondary agricultural education has consistently faced a shortage of teachers for the past several decades. Because there are not enough newly qualified teachers certified annually to fill all the vacancies, attrition must be addressed. The purpose of this research was to develop and pilot test an attrition risk assessment instrument. Items were…

Identification of Average Treatment Effects in Social Experiments under Alternative Forms of Attrition

ERIC Educational Resources Information Center

Huber, Martin

2012-01-01

As any empirical method used for causal analysis, social experiments are prone to attrition which may flaw the validity of the results. This article considers the problem of partially missing outcomes in experiments. First, it systematically reveals under which forms of attrition--in terms of its relation to observable and/or unobservable…

The Effects of Attrition on Baseline Comparability in Randomized Experiments in Education: A Meta-Analysis

ERIC Educational Resources Information Center

Valentine, Jeffrey C.; McHugh, Cathleen M.

2007-01-01

Using meta-analysis, randomized experiments in education that either clearly did or clearly did not experience student attrition were examined for the baseline comparability of groups. Results from 35 studies suggested that after attrition, the observed measures of baseline comparability of groups did not differ more than would be expected given…

Mechanical modelling of tooth wear

PubMed Central

Kallonen, Aki

2016-01-01

Different diets wear teeth in different ways and generate distinguishable wear and microwear patterns that have long been the basis of palaeodiet reconstructions. Little experimental research has been performed to study them together. Here, we show that an artificial mechanical masticator, a chewing machine, occluding real horse teeth in continuous simulated chewing (of 100 000 chewing cycles) is capable of replicating microscopic wear features and gross wear on teeth that resemble wear in specimens collected from nature. Simulating pure attrition (chewing without food) and four plant material diets of different abrasives content (at n = 5 tooth pairs per group), we detected differences in microscopic wear features by stereomicroscopy of the chewing surface in the number and quality of pits and scratches that were not always as expected. Using computed tomography scanning in one tooth per diet, absolute wear was quantified as the mean height change after the simulated chewing. Absolute wear increased with diet abrasiveness, originating from phytoliths and grit. In combination, our findings highlight that differences in actual dental tissue loss can occur at similar microwear patterns, cautioning against a direct transformation of microwear results into predictions about diet or tooth wear rate. PMID:27411727

Predictors of attrition from care at 2 years in a prospective cohort of HIV-infected adults in Tigray, Ethiopia

PubMed Central

Bucciardini, Raffaella; Fragola, Vincenzo; Abegaz, Teshome; Lucattini, Stefano; Halifom, Atakilt; Tadesse, Eskedar; Berhe, Micheal; Pugliese, Katherina; Fucili, Luca; Gregorio, Massimiliano Di; Mirra, Marco; Castro, Paola De; Terlizzi, Roberta; Tatarelli, Paola; Binelli, Andrea; Zegeye, Teame; Campagnoli, Michela; Vella, Stefano; Abraham, Loko; Godefay, Hagos

2017-01-01

Introduction Ethiopia has experienced rapid expansion of antiretroviral therapy (ART). However, as long-term retention in ART therapy is key for ART effectiveness, determinants of attrition need to be identified so appropriate interventions can be designed. Methods We used data from the ‘Cohort of African people Starting Antiretroviral therapy’ (CASA) project, a prospective study of a cohort of HIV-infected patients who started ART in seven health facilities (HFs). We analysed the data of patients who had started first-line ART between January 2013 and December 2014. The Kaplan–Meier method was used to estimate the probability of retention at different time points. The Cox proportional hazards model was used to identify factors associated with attrition. Results A total of 1198 patients were included in the study. Kaplan–Meier estimates of retention in care were 83.9%, 82.1% and 79.8% at 12, 18 and 24 months after starting ART, respectively. Attrition was mainly due to loss to follow-up, transferred-out patients and documented mortality. A multivariate Cox proportional hazard model showed that male sex, CD4 count <200 cells/µL and the type of HF were significantly associated with attrition. Conclusions The observed attrition differences according to gender suggest that separate interventions designed for women and men should be explored. Moreover, innovative strategies to increase HIV testing should be supported to avoid CD4 levels falling too low, a factor significantly associated with higher attrition in our study. Finally, specific studies to analyse the reasons for different levels of attrition among HFs are required. PMID:29082011

Are pilot trials useful for predicting randomisation and attrition rates in definitive studies: A review of publicly funded trials.

PubMed

Cooper, Cindy L; Whitehead, Amy; Pottrill, Edward; Julious, Steven A; Walters, Stephen J

2018-04-01

External pilot trials are recommended for testing the feasibility of main or confirmatory trials. However, there is little evidence that progress in external pilot trials actually predicts randomisation and attrition rates in the main trial. To assess the use of external pilot trials in trial design, we compared randomisation and attrition rates in publicly funded randomised controlled trials with rates in their pilots. Randomised controlled trials for which there was an external pilot trial were identified from reports published between 2004 and 2013 in the Health Technology Assessment Journal. Data were extracted from published papers, protocols and reports. Bland-Altman plots and descriptive statistics were used to investigate the agreement of randomisation and attrition rates between the full and external pilot trials. Of 561 reports, 41 were randomised controlled trials with pilot trials and 16 met criteria for a pilot trial with sufficient data. Mean attrition and randomisation rates were 21.1% and 50.4%, respectively, in the pilot trials and 16.8% and 65.2% in the main. There was minimal bias in the pilot trial when predicting the main trial attrition and randomisation rate. However, the variation was large: the mean difference in the attrition rate between the pilot and main trial was -4.4% with limits of agreement of -37.1% to 28.2%. Limits of agreement for randomisation rates were -47.8% to 77.5%. Results from external pilot trials to estimate randomisation and attrition rates should be used with caution as comparison of the difference in the rates between pilots and their associated full trial demonstrates high variability. We suggest using internal pilot trials wherever appropriate.

Factors associated with attrition from a randomized controlled trial of meaning-centered group psychotherapy for patients with advanced cancer

PubMed Central

Applebaum, Allison J.; Lichtenthal, Wendy G.; Pessin, Hayley A.; Radomski, Julia N.; Gökbayrak, N. Simay; Katz, Aviva M.; Rosenfeld, Barry; Breitbart, William

2013-01-01

Objective The generalizability of palliative care intervention research is often limited by high rates of study attrition. This study examined factors associated with attrition from a randomized controlled trial comparing meaning-centered group psychotherapy (MCGP), an intervention designed to help advanced cancer patients sustain or enhance their sense of meaning to the supportive group psychotherapy (SGP), a standardized support group. Methods Patients with advanced solid tumor cancers (n = 153) were randomized to eight sessions of either the MCGP or SGP. They completed assessments of psychosocial, spiritual, and physical well-being pretreatment, midtreatment, and 2 months post-treatment. Attrition was assessed in terms of the percent of participants who failed to complete these assessments, and demographic, psychiatric, medical, and study-related correlates of attrition were examined for the participants in each of these categories. Results The rates of attrition at these time points were 28.1%, 17.7%, and 11.1%, respectively; 43.1% of the participants (66 of 153) completed the entire study. The most common reason for dropout was patients feeling too ill. Attrition rates did not vary significantly between study arms. The participants who dropped out pretreatment reported less financial concerns than post-treatment dropouts, and the participants who dropped out of the study midtreatment had poorer physical health than treatment completers. There were no other significant associations between attrition and any demographic, medical, psychiatric, or study-related variables. Conclusions These findings highlight the challenge of maintaining advanced cancer patients in longitudinal research and suggest the need to consider alternative approaches (e.g., telemedicine) for patients who might benefit from group interventions but are too ill to travel. PMID:21751295

Are pilot trials useful for predicting randomisation and attrition rates in definitive studies: A review of publicly funded trials

PubMed Central

Whitehead, Amy; Pottrill, Edward; Julious, Steven A; Walters, Stephen J

2018-01-01

Background/aims: External pilot trials are recommended for testing the feasibility of main or confirmatory trials. However, there is little evidence that progress in external pilot trials actually predicts randomisation and attrition rates in the main trial. To assess the use of external pilot trials in trial design, we compared randomisation and attrition rates in publicly funded randomised controlled trials with rates in their pilots. Methods: Randomised controlled trials for which there was an external pilot trial were identified from reports published between 2004 and 2013 in the Health Technology Assessment Journal. Data were extracted from published papers, protocols and reports. Bland–Altman plots and descriptive statistics were used to investigate the agreement of randomisation and attrition rates between the full and external pilot trials. Results: Of 561 reports, 41 were randomised controlled trials with pilot trials and 16 met criteria for a pilot trial with sufficient data. Mean attrition and randomisation rates were 21.1% and 50.4%, respectively, in the pilot trials and 16.8% and 65.2% in the main. There was minimal bias in the pilot trial when predicting the main trial attrition and randomisation rate. However, the variation was large: the mean difference in the attrition rate between the pilot and main trial was −4.4% with limits of agreement of −37.1% to 28.2%. Limits of agreement for randomisation rates were −47.8% to 77.5%. Conclusion: Results from external pilot trials to estimate randomisation and attrition rates should be used with caution as comparison of the difference in the rates between pilots and their associated full trial demonstrates high variability. We suggest using internal pilot trials wherever appropriate. PMID:29361833

Dental evidence for wild tuber processing among Titicaca Basin foragers 7000 ybp.

PubMed

Watson, James T; Haas, Randall

2017-09-01

The objective of this work is to characterize dental wear in a skeletal sample dating to the Middle/Late Archaic period transition (8,000-6,700 cal. B.P.) from the Lake Titicaca Basin, Peru to better define subsistence behaviors of foragers prior to incipient sedentism and food production. The dental sample consists of 251 teeth from 11 individuals recovered from the site of Soro Mik'aya Patjxa (SMP), the earliest securely dated burial assemblage in the Lake Titicaca Basin and the only burial assemblage in the region from an unequivocal forager context. Occlusal surface wear was quantified according to Smith (1984) and Scott (1979a) to characterize diversity within the site and to facilitate comparison with other foraging groups worldwide. General linear modeling was used to assess observation error and principal axis analysis was used to compare molar wear rates and angles. Teeth were also examined for caries and specialized wear. Occlusal surface attrition is generally heavy across the dental arcade and tends to be flat among posterior teeth. Only one carious lesion was observed. Five of the 11 individuals exhibit lingual surface attrition of the maxillary anterior teeth (LSAMAT). Tooth wear rates, molar wear plane, and caries rates are consistent with terrestrial foraging and a diverse diet. The presence of LSAMAT indicates tuber processing. The results therefore contribute critical new data toward our understanding of forager diet in the Altiplano prior to plant and animal domestication in the south-central Andes. © 2017 Wiley Periodicals, Inc.

Attrition in nursing: perspectives from the national survey of college graduates.

PubMed

Crow, Stephen M; Smith, Steven A; Hartman, Sandra J

2005-01-01

Problems with attracting and retaining nurses during a tight labor market are compounded by some fundamental issues related to attrition from the field. It is important to recognize that, of the students who graduate from nursing schools each year and enter the field of nursing, significant attrition occurs during the first 5 years in the profession [www.aacn.nche.edu/media/backgrounders/shortagefacts.htmaacn.nche.edu (2002)]. This article uses data from the National Science Foundation's National Survey of College Graduates to examine various scenarios and possible reasons for why some nurses abandon their careers [www.nsf.gov/sbe/srs/snscg/start.htm (2003)]. In doing so, we consider entry into, and attrition from, the nursing profession at various stages. Using data from the National Survey of College Graduates, the initial evaluation suggests that, at points during the career, the individual confronts potential problems and issues which can lead to career attrition.

Study of Navy Enlisted Attrition: Race, Ethnicity, and Type of Occupation

DTIC Science & Technology

2008-09-01

technical job. Further research is recommended to explore these results and to suggest approaches that might assist in lowering attrition rates...technical job than to a technical one; in contrast, most minorities are far more likely to attrite when serving in a technical job. Further research is... HIGH QUALITY (HQ) STATUS ..........................33 IV. RESULTS ................................................35 A. DESCRIPTIVE SUMMARY OF THE

Investigating Attrition Trends in Order to Improve Student Retention

ERIC Educational Resources Information Center

Grebennikov, Leonid; Shah, Mahsood

2012-01-01

Purpose: This paper aims to focus on the experience of monitoring of first year student attrition in a large metropolitan multi-campus university during 2004-2010. The paper seeks to discuss the trends in student attrition which have been found and identify key issues which have been and need to be addressed by the university in order to increase…

Attrition and Retention of Special Education Teachers in an Urban High School

ERIC Educational Resources Information Center

Rhodes, Wendy

2012-01-01

Attrition is a problem among special education teachers in an urban high school in a southern part of the United States. A high school special education department served as the local setting. The department was unique due to a high teacher attrition rate and high percentage of teachers with less than five years of teaching experience. The purpose…

Stay, Play Or Give It Away? Students Continuing, Changing or Leaving University Study in First Year

ERIC Educational Resources Information Center

Long, Michael; Ferrier, Fran; Heagney, Margaret

2006-01-01

This study extends previous research on university attrition and course completion by its focus on the reasons for attrition and tracking the subsequent enrolment and other outcomes of students who discontinue their university studies. It also looks at older students as well as students from younger groups. It finds that attrition from first year…

Theoretical and Empirical Underpinnings of the What Works Clearinghouse Attrition Standard for Randomized Controlled Trials

ERIC Educational Resources Information Center

Deke, John; Chiang, Hanley

2014-01-01

Meeting the What Works Clearinghouse (WWC) attrition standard (or one of the attrition standards based on the WWC standard) is now an important consideration for researchers conducting studies that could potentially be reviewed by the WWC (or other evidence reviews). Understanding the basis of this standard is valuable for anyone seeking to meet…

Attrition in Developmental Psychology: A Review of Modern Missing Data Reporting and Practices

ERIC Educational Resources Information Center

Nicholson, Jody S.; Deboeck, Pascal R.; Howard, Waylon

2017-01-01

Inherent in applied developmental sciences is the threat to validity and generalizability due to missing data as a result of participant drop-out. The current paper provides an overview of how attrition should be reported, which tests can examine the potential of bias due to attrition (e.g., t-tests, logistic regression, Little's MCAR test,…

"Attrition Processes Out of Mathematics for Undergraduate Students." Attrition from Mathematics as a Social Process. Final Report.

ERIC Educational Resources Information Center

Maines, David R.; And Others

Investigated were those long-term processes which contribute to high rates of attrition for women out of mathematics. It is based on the contention that university students drop out of mathematics as a consequence of prior socialization, educational career contingencies, and goal commitment and career aspirations, with the mix of these factors…

Beyond the First-Year Experience: The Impact on Attrition of Student Experiences throughout Undergraduate Degree Studies in Six Diverse Universities

ERIC Educational Resources Information Center

Willcoxson, Lesley; Cotter, Julie; Joy, Sally

2011-01-01

In the face of difficult economic circumstances, increased competition and student diversity, attrition and retention have become issues of great significance to higher education institutions seeking to survive. A large body of work has explored the relationship between attrition and the first-year experience, but there has been little focus on…

Financial Bottom Line: Estimating the Cost of Faculty/Adjunct Turnover and Attrition for Online Programs

ERIC Educational Resources Information Center

Betts, Kristen S.; Sikorski, Bernadine

2008-01-01

Turnover and attrition of online faculty and adjunct faculty is a reality. While there are no reported national statistics or data on annual turnover/attrition for online faculty/adjunct, the overall costs of recruiting, training, and replacing faculty/adjunct can be staggering. Moreover, the short and long term effects of online faculty/adjunct…

Language Aptitude in First Language Attrition: A Study on Late Spanish-Swedish Bilinguals

ERIC Educational Resources Information Center

Bylund, Emanuel; Ramírez-Galan, Pedro

2016-01-01

Language aptitude remains one of the most understudied predictor variables in L1 attrition research. The current study seeks to address this gap by investigating the effects of language aptitude on L1 retention in late attriters. Forty L1 Spanish-L2 Swedish bilinguals living in Sweden participated in the study, along with 20 functionally…

The Cost of College Attrition at Four-Year Colleges & Universities. Policy Perspectives

ERIC Educational Resources Information Center

Raisman, Neal

2013-01-01

This report, an analysis of 1669 U.S. institutions, is a first-time study of the relationship of attrition to revenues lost in four-year public, private, and for-profit colleges and universities on an annual basis. The report is the result of a study investigating the financial impact of attrition on four-year colleges and universities. Other…

A Descriptive Study of the Impact of the Highly Qualified Teacher Requirement of NCLB on the Attrition of Special Education Personnel

ERIC Educational Resources Information Center

VanCise, Sandra A.

2013-01-01

According to current research, attrition of teachers in public schools throughout the United States has become increasingly worrisome, especially since the passage and inception of No Child Left Behind (2001) as well as the reauthorization of Individuals with Disabilities Act (1997). This rate of attrition remains especially problematic in the…

A Theoretical Model and Analysis of the Effect of Self-Regulation on Attrition from Voluntary Online Training

ERIC Educational Resources Information Center

Sitzmann, Traci

2012-01-01

A theoretical model is presented that examines self-regulatory processes and trainee characteristics as predictors of attrition from voluntary online training in order to determine who is at risk of dropping out and the processes that occur during training that determine when they are at risk of dropping out. Attrition increased following declines…

Diet and age-at-death determinations from molar attrition. A review related to the low countries.

PubMed

Maat, G J

2001-06-01

To elucidate the impact of diet on age-at-death determinations based on molar attrition a comparison was made between the established rate of attrition in three populations; a pre-mediaeval (British), a late mediaeval (Dutch) and a 17-18th century (Dutch) (western European). It appeared that the rate decreased dramatically during the overall time span and that this change was probably diet related and owing to the coarseness of foodstuffs. This result strongly indicated that molar age-attrition tables should only be used for age-at-death determinations if their application is restricted to a particular cultural period and diet.

A guide to the clinical management of attrition.

PubMed

Rees, J S; Somi, S

2018-03-09

Attrition is an enigmatic condition often found in older individuals and often as a result of bruxism which can take place as a result of either day bruxism, night bruxism or both. Various studies and systemic reviews clearly shown that tooth wear is an age-related phenomena and the last Adult Dental Health Survey showed that 15% of participants showed moderate wear and 3% severe wear with 80% of patients over 50 years of age showing signs of wear. This review examines current theories around the aetiological factors contributing to attrition together with the clinical management of attrition focusing on minimal intervention where possible.

An Integrative Review of Factors Associated with Patient Attrition from Community Health Worker Programs that Support Diabetes Self-Care.

PubMed

Merius, Heidy N; Rohan, Annie J

2017-01-01

An integrative review was conducted using PubMed and CINAHL databases to answer: What is known about adult attrition from community health worker (CHW) programs on diabetes self-care? The 14 articles described patients of multiple races who were mainly of lower socioeconomic status. CHW interventions were given in individual meetings and/or group sessions. Incentives to reduce attrition came in different forms. Barriers involved transportation, family obligations, and scheduling conflicts. Attrition from these programs is a multifactorial problem. Alleviating transportation barrier appears to be protective. Program planners should consider these barriers when planning CHW programs.

Attrition of full-time faculty from schools of nursing with baccalaureate and graduate programs, 2010 to 2011.

PubMed

Fang, Di; Bednash, Geraldine D

2014-01-01

The shortage of qualified faculty has been consistently reported as a major barrier impeding acceptance of all qualified applicants into nursing programs. In addition to faculty recruitment, the attrition of faculty is also a concern for schools of nursing. In this study, we found that nationally 11.8% of full-time faculty who worked in 2010 left their full-time jobs by 2011. Nearly half of total attrition, or 5.7% of full-time faculty members, were related to leaving for nonacademic nursing positions, whereas another 20% of attrition, or 2.4% of full-time faculty, resulted from retirement. Nearly 20% of faculty egressions, or 2.2% of full-time faculty, was due to leaving for nursing administrative positions or full-time faculty positions in an academic setting. Leaving for part-time faculty positions made up slightly more than 10% of faculty attrition or 1.3% of full-time faculty. Our bivariate analysis identifies distinctive academic and demographic profiles of faculty who left full-time positions for different reasons, and our multivariate analysis further shows that different individual and institutional attributes are significantly associated with different types of attrition. Copyright © 2014 Elsevier Inc. All rights reserved.

Attrition Bias in Panel Data: A Sheep in Wolf's Clothing? A Case Study Based on the Mabel Survey.

PubMed

Cheng, Terence C; Trivedi, Pravin K

2015-09-01

This paper investigates the nature and consequences of sample attrition in a unique longitudinal survey of medical doctors. We describe the patterns of non-response and examine if attrition affects the econometric analysis of medical labour market outcomes using the estimation of physician earnings equations as a case study. We compare the econometric gestimates obtained from a number of different modelling strategies, which are as follows: balanced versus unbalanced samples; an attrition model for panel data based on the classic sample selection model; and a recently developed copula-based selection model. Descriptive evidence shows that doctors who work longer hours, have lower years of experience, are overseas trained and have changed their work location are more likely to drop out. Our analysis suggests that the impact of attrition on inference about the earnings of general practitioners is small. For specialists, there appears to be some evidence for an economically significant bias. Finally, we discuss how the top-up samples in the Medicine in Australia: Balancing Employment and Life survey can be used to address the problem of panel attrition. Copyright © 2015 John Wiley & Sons, Ltd.

Dental cervical lesions associated with occlusal erosion and attrition.

PubMed

Khan, F; Young, W G; Shahabi, S; Daley, T J

1999-09-01

Acid demineralization of teeth causes occlusal erosion and attrition, and shallow and wedge-shaped cervical lesions putatively involving abfraction. From 250 patients with tooth wear, 122 with cervical lesions were identified. From epoxy resin replicas of their dentitions, associations of occlusal attrition or erosion or no wear with cervical lesions were recorded at 24 tooth sites (total 2928 sites). Criteria used to discriminate occlusal attrition from erosion, and shallow from grooved, wedge-shaped or restored cervical lesions were delineated by scanning electron microscopy. A 96 per cent association was found between occlusal and cervical pathology. Shallow cervical lesions were more commonly found in association with occlusal erosion. Wedge-shaped lesions were found equally commonly in association with occlusal erosion, as with attrition. Grooved and restored cervical lesions were uncommon. Differences were appreciated in the associations within incisor, canine, premolar and molar tooth sites which related more to the site-specificity of dental erosion than to attrition from occlusal forces. Non-carious lesions on teeth then have multifactorial aetiology and pathogenesis in which erosion and salivary protection play central roles. Dentists should primarily consider erosion in the diagnosis, prevention and treatment of tooth wear.

Structural and spectroscopic study of mechanically synthesized SnO{sub 2} nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vij, Ankush, E-mail: vij-anx@yahoo.com; Kumar, Ravi; Presently at Beant College of Engineering and Technology, Gurdaspur-143521

2016-05-23

We report the single step synthesis of SnO{sub 2} nanostructures using high energy mechanical attrition method. X-ray diffraction (XRD) pattern reveals the single phase rutile structure with appreciable broadening of diffraction peaks, which is a signature of nanostructure formation. The average crystallite size of SnO{sub 2} nanostructures has been calculated to be ~15 nm. The micro-Raman study reveals the shifting of A{sub 1g} Raman mode towards lower wave number, which is correlated with the nanostructure formation.

Optimization of Limestone Feed Size of a Pressurized Fluidized Bed Combustor

NASA Astrophysics Data System (ADS)

Shimizu, Tadaaki; Saastamolnen, Jaakko

Limestone attrition is a major cause of loss of limestone during pressurized fluidized bed combustion. In the authors' previous works, the analysis of published results of solid attrition and desulfurization was conducted to determine the attrition rate expression. The specific attrition rate (rate of decrease in diameter) was estimated to be second order with respect to particle diameter in the previous work. This rate expression implies that reduction of feed size of limestone is effective for suppression of loss of limestone by attrition. However, too much grinding of raw limestone will increase the content of fine particles that are readily elutriated by gas stream and do not contribute to the sulfur capture. In this work, modeling works are conducted for particle attrition and desulfurization in order to predict the effect of feed size of limestone on total consumption of limestone and desulfurization is discussed. Optimum particle size to suppress limestone consumption was approximately 0.7 mm (as D p50 ). However, the control of solid drain rate from the bottom was found to have more influence on total limestone consumption rate. Emissions of SO2 from low sulfur coal (S=0.33%) could be sufficiently low irrespective of limestone feed size but SO2 emissions from coals with higher sulfur content than 0.5% were anticipated to increase drastically. Such drastic change in SO2 emissions with the change in sulfur content is attributable to non-linear nature of reaction rate for attrition-enhanced desulfurization by limestone.

Attrition in surgical residency programmes: Causes and effects.

PubMed

Nadeem, Mehwash; Effendi, M Shahrukh; Hammad Ather, M

2014-03-01

To determine the rate and trend of attrition from a surgical residency programme and to identify the reasons for attrition. A questionnaire-based survey was conducted at a university hospital. Separate questionnaires were designed for residents and programme directors (PDs). The residents who left the training voluntarily from one of the five surgical residency programmes (i.e., general surgery, orthopaedics, neurosurgery, otorhinolaryngology and urology) during the academic years 2005-2011 were identified from a departmental database. The residents who did not respond after three attempts at contact, or those who refused to participate, were excluded. During the last 6 years, 106 residents were recruited; 84 (78%) were men, of whom 34.5% left the programme voluntarily. Of 22 women, half (54%) left the programme voluntarily (P = 0.07). The overall 6-year attrition rate was 39%. The reasons identified for attrition, in descending order, were personal reasons, attitude of senior residents or faculty, and change of specialty. None of the residents cited an excess workload as a reason for their leaving the programme. About 40% rejoined the same specialty after leaving, while 35% chose a different specialty (80% chose a different surgical subspecialty and 20% chose medicine). There was a significant discrepancy in the perspective of residents and PDs about the reasons for attrition. Attrition among surgical residents, in particular woman residents, is high. Personal reasons and interpersonal relations were the most commonly cited reasons. Programme managers and residents have significantly different perspectives, again an indication of a communication gap.

Development of a Mechanism and Standards for the Assessment of Adult Basic Education Students as They Relate to Post-Secondary Vocational Education Programs. Final Report.

ERIC Educational Resources Information Center

Grosskoph, Arlys; And Others

The purpose of this project was to develop a process that would reduce the attrition rate of adult basic education students entering occupational programs. To accomplish this goal, adult basic education students in occupational programs, adult basic education students who had dropped out of occupational programs, and their instructors were…

"Should I Stay or Should I Go?": Unpacking Teacher Attrition/Retention as an Educational Issue

ERIC Educational Resources Information Center

Kelchtermans, Geert

2017-01-01

The paper starts from the observation that teacher attrition/retention seems to be a wicked issue: it seems to have strong face validity and a commonsense meaning, but the literature doesn't provide a clear and distinctive definition. In the first section, the author analyzes the different ways in which the issue of teacher attrition and retention…

The Effect of Different Enlistment Ages on First-Term Attrition Rate

DTIC Science & Technology

2014-03-01

enlistment age, other variables that may affect attrition are also evaluated; gender , marital status, education level, race, annual state ...Unemployment rates by states were included in the regressions. The study concluded that enlistment ages do significantly affect the attrition of...education level; different enlistment age dummies between 18 and 42; female or male; and AFQT Cat. Unemployment rates by states were included in the

The Effect of Intentional Remediation to Mitigate Attrition Rates in a Nursing Program: An Action Research Study

ERIC Educational Resources Information Center

O'Neal, Michelle

2013-01-01

A trend in high end-of-year academic attrition creates a negative impact on an institution's mission and in the community. In the community, attrition reduces the number of potential nurses during a looming nursing shortage predicted by the American Nurses' Association (2001). The mission of one two-year college is to produce successful nursing…

Attrition in a Large Scale Longitudinal Study of the Elderly: The Role of Health-Status Variables.

ERIC Educational Resources Information Center

Horgas, Ann L.; And Others

In a longitudinal study, subject attrition constitutes a potential threat to the usefulness of data collected from subjects remaining in later waves of the study. If attrition is selective, then the sample at later waves of the study may be representative of a different population than that represented at the outset of the study. This study…

Determinants of First-Term Attrition for Enlisted and Officer Selected Marine Corps Reservists

DTIC Science & Technology

2015-03-01

FIRST-TERM ATTRITION FOR ENLISTED AND OFFICER SELECTED MARINE CORPS RESERVISTS by Ugur Ugurbas Mustafa Korkmaz March 2015 Thesis Advisors...ATTRITION FOR ENLISTED AND OFFICER SELECTED MARINE CORPS RESERVISTS Ugur Ugurbas Captain, Turkish Army B.S., Turkish Army Academy, 2006 Mustafa...the degree of MASTER OF SCIENCE IN MANAGEMENT from the NAVAL POSTGRADUATE SCHOOL March 2015 Authors: Ugur Ugurbas Mustafa

The Dissertation Story: What Is the Relationship between the Officer Candidate School Attrition Rate and Officer Training Command, Naval Service Training Command and Navy Recruiting Command Leadership Intervention?

DTIC Science & Technology

2013-03-01

attrition (Goodstadt, 1981). Kubisiak, et al. contend that leaders should consider attrition a negative occurrence and that each leader should develop...related to the information, and the consequences associated with the options. The ability to ruminate before acting when presented with new information or

Retention and Attrition of Students in Higher Education: Challenges in Modern Times to What Works

ERIC Educational Resources Information Center

Maher, Marguerite; Macallister, Helen

2013-01-01

Retention and attrition rates in higher education have long been a focus of research. This paper presents findings of a single case study, undertaken in a School of Education, which identify important strategies that have led to attrition of five to eight per cent, compared with 18 per cent cross the education sector in Australia (Department of…

Biases in Estimating Treatment Effects Due to Attrition in Randomized Controlled Trials and Cluster Randomized Controlled Trials: A Simulation Study

ERIC Educational Resources Information Center

Dong, Nianbo; Lipsey, Mark W.

2011-01-01

Attrition occurs when study participants who were assigned to the treatment and control conditions do not provide outcome data and thus do not contribute to the estimation of the treatment effects. It is very common in experimental studies in education as illustrated, for instance, in a meta-analysis studying "the effects of attrition on baseline…

Health workforce deployment, attrition and density in East wollega zone, Western ethiopia.

PubMed

Hailemichael, Yohannes; Jira, Challi; Girma, Belayneh; Tushune, Kora

2010-03-01

In East Wollega Zone, despite the success in creating considerable number of health facilities, short-age of health personnel, geographical imbalance and increasing attrition is found to be a persistent barrier to the effectiveness of the health system. However, available data is not rich enough to provide reliable information as to what extent these problems exist in the Zone. Hence, this study was conducted to assess health workforce density, deployment and attrition in East Wollega Zone. A six years retrospective record review from 2000-2005 was conducted between February 1, and March 30, 2006 in eleven randomly selected districts of East Wollega Zone. Data obtained from records and interviews made with selected resource persons were organized by triangulating quantitatively and qualitatively. Quantitative data was analyzed using SPSS 12.01 for windows and thematic frame work analysis was used for qualitative data. Health workforce deployment rate for the years 2000-2005 ranged from 8.2% to 15.4 %. In contrast, attrition rate for the same period ranged from 2.9 % to 8.5 %. Attrition rate for the time after decentralization (2003-2005) was nearly two times greater than before decentralization (OR, 2.04, CI, 1.51, 2.85, P=0.00). Moreover, attrition rate was nearly three times greater for a high level professional when compared to the lower level (OR, 3.15, CI , 2.63, 4.37, P=0.00). Attrition rate for males was two times higher as compared to females (OR, 2.07, CI, 1.67, 3.74, P=0.00). About (26.3%) of all health workers and (36.7%) of nurses and midwives were deployed to the capital town of the zone. Factors identified as most likely cause for the lower deployment and higher attritions were budget related constraints, lack of continuing education opportunity and poor career development. The number of health personnel in East Wollega was low both by international standards and relative to the national density. Moreover, attrition was higher for the time after decentralization process. Hence, measures that seek to increase the size of the health workforce through increased recruitment, higher retention of existing staff and better geographical balance have to be urgently explored.

Low risk of attrition among adults on antiretroviral therapy in the Rwandan national program: a retrospective cohort analysis of 6, 12, and 18 month outcomes.

PubMed

Nuwagaba-Biribonwoha, Harriet; Jakubowski, Aleksandra; Mugisha, Veronicah; Basinga, Paulin; Asiimwe, Anita; Nash, Denis; Elul, Batya

2014-08-29

We report levels and determinants of attrition in Rwanda, one of the few African countries with universal ART access. We analyzed data abstracted from health facility records of a nationally representative sample of adults [≥ 18 years] who initiated ART 6, 12, and 18 months prior to data collection; and collected facility characteristics with a health facility assessment questionnaire. Weighted proportions and rates of attrition [loss to follow-up or death] were calculated, and patient- and health facility-level factors associated with attrition examined using Cox proportional hazard models. 1678 adults initiated ART 6, 12 and 18 months prior to data collection, with 1508 person-years [PY] on ART. Attrition was 6.8% [95% confidence interval [CI] 6.0-7.8]: 2.9% [2.4-3.5] recorded deaths and 3.9% [3.4-4.5] lost to follow-up. Population attrition rate was 7.5/100 PY [6.1-9.3]. Adjusted hazard ratio [aHR] for attrition was 4.2 [3.0-5.7] among adults enrolled from in-patient wards [vs 2.2 [1.6-3.0] from PMTCT, ref: VCT]. Compared to adults who initiated ART 18 months earlier, aHR for adults who initiated ART 12 and 6 months earlier was 1.8 [1.3-2.5] and 1.3 [0.9-1.9] respectively. Male aHR was 1.4 [1.0-1.8]. AHR of adults enrolled at urban health facilities was 1.4 [1.1-1.8, ref: rural health facilities]. AHR for adults with CD4+ ≥ 200 cells/μL vs <200 cells/μL was 0.8 [0.6-1.0]; and adults attending facilities with performance-based financing since 2004-2006 [vs. 2007-2008] had aHR 0.8 [0.6-0.9]. Attrition was low in the Rwandan national program. The above patient and facility correlates of attrition can be the focus of interventions to sustain high retention.

Applications of tribology to determine attrition by wear of particulate solids in CFB systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bayham, Samuel C.; Breault, Ronald; Monazam, Esmail

In recent years, much attention has been focused on the development of novel technologies for carbon capture and chemicals production that utilize a circulating fluidized bed (CFB) configuration; examples include chemical looping combustion and circulation of temperature swing adsorbents in a CFB configuration for CO 2 capture. A major uncertainty in determining the economic feasibility of these technologies is the required solids makeup rate, which, among other factors, is due to impact and wear attrition at various locations, including standpipes, cyclones, and the gas jets in fluid beds. While correlations have been developed that estimate the attrition rates at thesemore » areas, these correlations are dependent on constants that are uncertain without extensive experiment in the corresponding unit operation. Thus, it is difficult to determine the attrition rate a priori without performing extensive experiments on the materials or scaling up entirely. In this work, the authors outline a methodology for predictive attrition based on fundamental material properties from fields of tribology—specifically, the study of wear—to the knowledge of forces and sliding distances determined from hydrodynamic models to develop basic attrition models for novel CFB systems. The equations are derived for the standpipe and cyclone, which are common components found in CFBs, and the cyclone equation is compared to experimental data of attrition in the literature. The cyclone equation derived in this work results in an abrasion rate based on (1) material properties such as particle density and hardness, (2) inlet velocity, and (3) cyclone geometry. According to this equation, increasing the diameter of the cyclone and the solids inlet velocity tends to increase the rate of abrasion of the catalyst, while decreasing the hardness increases the abrasion rate. The functionality of the increasing attrition rate with velocity increase implies that increasing the efficiency of the cyclone may also increase the attrition rate via abrasion. With modifications to the severity coefficient term to include the solids loading, the cyclone equation derived in this work fits data from Reppenhagen and Werther with a coefficient of determination (R2) of 92%.« less

Positive trends in neurosurgery enrollment and attrition: analysis of the 2000-2009 female neurosurgery resident cohort.

PubMed

Renfrow, Jaclyn J; Rodriguez, Analiz; Liu, Ann; Pilitsis, Julie G; Samadani, Uzma; Ganju, Aruna; Germano, Isabelle M; Benzil, Deborah L; Wolfe, Stacey Quintero

2016-03-01

Women compose a minority of neurosurgery residents, averaging just over 10% of matched applicants per year during this decade. A recent review by Lynch et al. raises the concern that women may be at a higher risk than men for attrition, based on analysis of a cohort matched between 1990 and 1999. This manuscript aims to characterize the trends in enrollment, attrition, and postattrition careers for women who matched in neurosurgery between 2000 and 2009. Databases from the American Association of Neurological Surgeons (AANS) and the American Board of Neurological Surgery (ABNS) were analyzed for all residents who matched into neurosurgery during the years 2000-2009. Residents were sorted by female gender, matched against graduation records, and if graduation was not reported from neurosurgery residency programs, an Internet search was used to determine the residents' alternative path. The primary outcome was to determine the number of women residents who did not complete neurosurgery training programs during 2000-2009. Secondary outcomes included the total number of women who matched into neurosurgery per year, year in training in which attrition occurred, and alternative career paths that these women chose to pursue. Women comprised 240 of 1992 (12%) matched neurosurgery residents during 2000-2009. Among female residents there was a 17% attrition rate, compared with a 5.3% male attrition rate, with an overall attrition rate of 6.7%. The majority who left the field did so within the first 3 years of neurosurgical training and stayed in medicine--pursuing anesthesia, neurology, and radiology. Although the percentage of women entering neurosurgical residency has continued to increase, this number is still disproportionate to the overall number of women in medicine. The female attrition rate in neurosurgery in the 2000-2009 cohort is comparable to that of the other surgical specialties, but for neurosurgery, there is disparity between the male and female attrition rates. Women who left the field tended to stay within medicine and usually pursued a neuroscience-related career. Given the need for talented women to pursue neurosurgery and the increasing numbers of women matching annually, the recruitment and retention of women in neurosurgery should be benchmarked and assessed.

Applications of tribology to determine attrition by wear of particulate solids in CFB systems

DOE PAGES

Bayham, Samuel C.; Breault, Ronald; Monazam, Esmail

2016-11-03

In recent years, much attention has been focused on the development of novel technologies for carbon capture and chemicals production that utilize a circulating fluidized bed (CFB) configuration; examples include chemical looping combustion and circulation of temperature swing adsorbents in a CFB configuration for CO 2 capture. A major uncertainty in determining the economic feasibility of these technologies is the required solids makeup rate, which, among other factors, is due to impact and wear attrition at various locations, including standpipes, cyclones, and the gas jets in fluid beds. While correlations have been developed that estimate the attrition rates at thesemore » areas, these correlations are dependent on constants that are uncertain without extensive experiment in the corresponding unit operation. Thus, it is difficult to determine the attrition rate a priori without performing extensive experiments on the materials or scaling up entirely. In this work, the authors outline a methodology for predictive attrition based on fundamental material properties from fields of tribology—specifically, the study of wear—to the knowledge of forces and sliding distances determined from hydrodynamic models to develop basic attrition models for novel CFB systems. The equations are derived for the standpipe and cyclone, which are common components found in CFBs, and the cyclone equation is compared to experimental data of attrition in the literature. The cyclone equation derived in this work results in an abrasion rate based on (1) material properties such as particle density and hardness, (2) inlet velocity, and (3) cyclone geometry. According to this equation, increasing the diameter of the cyclone and the solids inlet velocity tends to increase the rate of abrasion of the catalyst, while decreasing the hardness increases the abrasion rate. The functionality of the increasing attrition rate with velocity increase implies that increasing the efficiency of the cyclone may also increase the attrition rate via abrasion. With modifications to the severity coefficient term to include the solids loading, the cyclone equation derived in this work fits data from Reppenhagen and Werther with a coefficient of determination (R2) of 92%.« less

High pre-diagnosis attrition among patients with presumptive MDR-TB: an operational research from Bhopal district, India.

PubMed

Shewade, Hemant Deepak; Kokane, Arun M; Singh, Akash Ranjan; Verma, Manoj; Parmar, Malik; Chauhan, Ashish; Chahar, Sanjay Singh; Tiwari, Manoj; Khan, Sheeba Naz; Gupta, Vivek; Tripathy, Jaya Prasad; Nagar, Mukesh; Singh, Sanjai Kumar; Mehra, Pradeep Kumar; Kumar, Ajay Mv

2017-04-04

Pre-diagnosis attrition needs to be addressed urgently if we are to make progress in improving MDR-TB case detection and achieve universal access to MDR-TB care. We report the pre-diagnosis attrition, along with factors associated, and turnaround times related to the diagnostic pathway among patient with presumptive MDR-TB in Bhopal district, central India (2014). Study was conducted under the Revised National Tuberculosis Control Programme setting. It was a retrospective cohort study involving record review of all registered TB cases in Bhopal district that met the presumptive MDR-TB criteria (eligible for DST) in 2014. In quarter 1, Line Probe Assay (LPA) was used if sample was smear/culture positive. Quarter 2 onwards, LPA and Cartridge-based Nucleic Acid Amplification Test (CbNAAT) was used for smear positive and smear negative samples respectively. Pre-diagnosis attrition was defined as failure to undergo DST among patients with presumptive MDR-TB (as defined by the programme). Of 770 patients eligible for DST, 311 underwent DST and 20 patients were diagnosed as having MDR-TB. Pre-diagnosis attrition was 60% (459/770). Among those with pre-diagnosis attrition, 91% (417/459) were not identified as 'presumptive MDR-TB' by the programme. TAT [median (IQR)] to undergo DST after eligibility was 4 (0, 10) days. Attrition was more than 40% across all subgroups. Age more than 64 years; those from a medical college; those eligible in quarter 1; patients with presumptive criteria 'previously treated - recurrent TB', 'treatment after loss-to-follow-up' and 'previously treated-others'; and patients with extra-pulmonary TB were independent risk factors for not undergoing DST. High pre-diagnosis attrition was contributed by failure to identify and refer patients. Attrition reduced modestly with time and one factor that might have contributed to this was introduction of CbNAAT in quarter 2 of 2014. General health system strengthening which includes improvement in identification/referral and patient tracking with focus on those with higher risk for not undergoing DST is urgently required.

Factors associated with long-term antiretroviral therapy attrition among adolescents in rural Uganda: a retrospective study.

PubMed

Okoboi, Stephen; Ssali, Livingstone; Yansaneh, Aisha I; Bakanda, Celestin; Birungi, Josephine; Nantume, Sophie; Okullu, Joanne Lyavala; Sharp, Alana R; Moore, David M; Kalibala, Samuel

2016-01-01

As access to antiretroviral therapy (ART) increases, the success of treatment programmes depends on ensuring high patient retention in HIV care. We examined retention and attrition among adolescents in ART programmes across clinics operated by The AIDS Support Organization (TASO) in Uganda, which has operated both facility- and community-based distribution models of ART delivery since 2004. Using a retrospective cohort analysis of patient-level clinical data, we examined attrition and retention in HIV care and factors associated with attrition among HIV-positive adolescents aged 10-19 years who initiated ART at 10 TASO clinics between January 2006 and December 2011. Retention in care was defined as the proportion of adolescents who had had at least one facility visit within the six months prior to 1 June 2013, and attrition was defined as the proportion of adolescents who died, were lost to follow-up, or stopped treatment. Descriptive statistics and Cox proportional hazards regression models were used to determine the levels of retention in HIV care and the factors associated with attrition following ART initiation. A total of 1228 adolescents began ART between 2006 and 2011, of whom 57% were female. The median duration in HIV care was four years (IQR=3-6 years). A total of 792 (65%) adolescents were retained in care over the five-year period; 36 (3%) had died or transferred out and 400 (32%) were classified as loss to follow-up. Factors associated with attrition included being older (adjusted hazard ratio (AHR)=1.38, 95% confidence interval (CI) 1.02-1.86), having a higher CD4 count (250+ cells/mm(3)) at treatment initiation (AHR=0.49, 95% CI 0.34-0.69) and HIV care site with a higher risk of attrition among adolescents in Gulu (AHR=2.26; 95% CI 1.27-4.02) and Masindi (AHR=3.30, 95% CI 1.87-5.84) and a lower risk of attrition in Jinja (AHR=0.24, 95% CI 0.08-0.70). Having an advanced WHO clinical stage at initiation was not associated with attrition. We found an overall retention rate of 65%, which is comparable to rates achieved by TASO's adult patients and adolescents in other studies in Africa. Variations in the risk of attrition by TASO treatment site and by clinical and demographic characteristics suggest the need for early diagnosis of HIV infection, use of innovative approaches to reach and retain adolescents living with HIV in treatment and identifying specific groups, such as older adolescents, that are at high risk of dropping out of treatment for targeted care and support.

Examine the Impact of Training Duration on Retention

DTIC Science & Technology

2012-09-01

attrition in Japanese contexts (pp. 169-200). Oxford: Oxford University Press. Neisser , U . (1984). Interpreting Harry Bahrick’s discovery: What confers...17. LIMITATION OF ABSTRACT 18. NUMBER OF PAGES 19a. NAME OF RESPONSIBLE PERSON Surface, Eric A. a. REPORT U b. ABSTRACT U c. THIS PAGE... U UU (SAR) 42 19b. TELEPHONE NUMBER (include area code) 919-480-2751 Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39.18

Job insecurity and sickness absence: correlations between attrition and absence in 36 occupational groups.

PubMed

Blekesaune, Morten

2012-11-01

To investigate how job insecurity, as indicated by attrition rates out of employment, affects sickness absence among remaining workers. A longitudinal analysis investigated how the percentage of workers absent due to sickness was affected by attrition out of employment in Norwegian Labour Force Surveys from 1997 to 2005, between 31 quarterly observations at the level of 36 occupational groups. Rising attrition is associated with more sickness absence. Previous research has argued that job insecurity can lead to more absence because of a stressor effect as well as to less absence because of a disciplinary effect. This research indicates that the stressor effect is stronger than the disciplinary effect.

Medical Attrition from Commanders Training in the Israeli Defense Forces (IDF): A Cross-sectional Study on 23,841 Soldiers.

PubMed

Schwartz, Oren; Kanevsky, Boris; Kutikov, M A J Sergey; Olsen, Cara H; Dudkiewicz, Israel

2018-03-14

Attrition from training is associated with substantial financial and personnel loss. There is a plethora of medical literature and research of attrition rates related to initial/phase 1 training (basic combat training); however, the analysis of second phase training (commanders training, consisting of schools that qualify junior commanders and officers for infantry and non-infantry combat units) is limited. The purpose of this study is to perform a comprehensive survey regarding to medical attrition from commanders training in the IDF (Israeli Defense Forces) in order to present the commanders of the IDF a detailed situation report that will serve as an evidence-based platform for future policy planning and implementation. A cross-sectional study including all soldiers (23,841) who participated in commanders training in the IDF in the period of 2012-2015 was performed. Soldiers for whom the attrition reason (medical or not medical) was missing were excluded from this study. Data were collected from the adjutancy-computerized system as well as the IDF's computerized medical consultation records package (CPR). Descriptive statistics were performed using mean, standard deviation, and median in order to express results. For the determination of statistical significance, chi-square test, Student's t-test, and Poisson regression models were used. Out of 23,841 soldiers that participated in this study, 75% (17,802) were males and 25% (6,039) were females. The overall attrition rate was 0.7% (164). The attrition rate for males was 0.86% (148 out of 17,082 males) and 0.26% (16 out of 6,039 females) for females. After adjusting for training unit, age, and BMI, the risk for attrition was 1.6 (160%) times higher for males as compared with females, and this result was statistically significant (IRR = 1.6, p = 0.01, CI 1.1, 2.2). The re-injury rate was 41% (68 out of 164 soldiers). The three most frequent diagnoses for attrition were orthopedics (66%), general surgery diagnoses (12%), and diagnoses related to internal medicine (11%). Out of 107 soldiers that attired due to orthopedic reasons, 36 (34%) suffered from calf and ankle injuries, 22 (21%) attired due to diagnoses related to the lower back, and 22 (21%) attired due to diagnoses related to the knee region. The highest attrition rate was encountered in the school for infantry junior command (2.2%) and the lowest rate was encountered in the officer training school for non-infantry units (0.11%). After adjusting for age and BMI, the risk for ankle injury was 2.55 (255%) times higher for soldiers in the school for infantry junior command as compared with soldiers in the officer school for infantry units (IRR = 2.55 p = 0.017, CI 1.18, 5.47). The attrition rate from commanders training in the IDF is low, and at this point, however, due to lack of uniform criteria for attrition, it cannot serve as an objective measure. We suggest measuring and discussing overuse injury rates (which is the most frequent cause of attrition), instead. Based on our results, we recommend an implementation of a better medical screening policy in order to reduce the re-injury rates during commanders training.

Post-inpatient attrition from care "as usual" in veterans with multiple psychiatric admissions.

PubMed

Bowersox, Nicholas W; Saunders, Stephen M; Berger, Bertrand

2013-12-01

Disengagement from outpatient care following psychiatric hospitalization is common in high-utilizing psychiatric patients and contributes to intensive care utilization. To investigate variables related to treatment attrition, a range of demographic, diagnostic, cognitive, social, and behavioral variables were collected from 233 veterans receiving inpatient psychiatric services who were then monitored over the following 2 years. During the follow-up period, 88.0 % (n = 202) of patients disengaged from post-inpatient care. Attrition was associated with male gender, younger age, increased expectations of stigma, less short-term participation in group therapy, and poorer medication adherence. Of those who left care, earlier attrition was predicted by fewer prior-year inpatient psychiatric days, fewer lifetime psychiatric hospitalizations, increased perceived treatment support from family, and less short-term attendance at psychiatrist appointments. Survival analyses were used to analyze the rate of attrition of the entire sample as well as the sample split by short-term group therapy attendance. Implications are discussed.

Relationships between age and dental attrition in Australian aboriginals.

PubMed

Richards, L C; Miller, S L

1991-02-01

Tooth wear scores (ratios of exposed dentin to total crown area) were calculated from dental casts of Australian Aboriginal subjects of known age from three populations. Linear regression equations relating attrition scores to age were derived. The slope of the regression line reflects the rate of tooth wear, and the intercept is related to the timing of first exposure of dentin. Differences in morphology between anterior and posterior teeth are reflected in a linear relationship between attrition scores and age for anterior teeth but a logarithmic relationship for posterior teeth. Correlations between age and attrition range from less than 0.40 for third molars (where differences in the eruption and occlusion of the teeth resulted in different patterns of wear) to greater than 0.80 for the premolars and first molars. Because of the generally high correlations between age and attrition, it is possible to estimate age from the extent of tooth wear with confidence limits of the order of +/- 10 years.

Highly Attrition Resistant Zinc Oxide-Based Sorbents for H2S Removal by Spray Drying Technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryu, C.K.; Lee, J.B.; Ahn, D.H.

2002-09-19

Primary issues for the fluidized-bed/transport reactor process are high attrition resistant sorbent, its high sorption capacity and regenerability, durability, and cost. The overall objective of this project is the development of a superior attrition resistant zinc oxide-based sorbent for hot gas cleanup in integrated coal gasification combined cycle (IGCC). Sorbents applicable to a fluidized-bed hot gas desulfurization process must have a high attrition resistance to withstand the fast solid circulation between a desulfurizer and a regenerator, fast kinetic reactions, and high sulfur sorption capacity. The oxidative regeneration of zinc-based sorbent usually initiated at greater than 600 C with highly exothermicmore » nature causing deactivation of sorbent as well as complication of sulfidation process by side reaction. Focusing on solving the sorbent attrition and regenerability of zinc oxide-based sorbent, we have adapted multi-binder matrices and direct incorporation of regeneration promoter. The sorbent forming was done with a spray drying technique that is easily scalable to commercial quantity.« less

Telomeric attrition with age and temperature in Eastern mosquitofish ( Gambusia holbrooki)

NASA Astrophysics Data System (ADS)

Rollings, Nicky; Miller, Emily; Olsson, Mats

2014-03-01

Telomeric attrition has repeatedly been found to correlate with the ageing of organisms; however, recent research is increasingly showing that the determinants of attrition dynamics are not well understood. This study examined the relative telomere lengths in Eastern mosquitofish, Gambusia holbrooki, kept at different temperatures and at different ages. Newly born fry were randomly selected for one of four treatment groups: 20, 30, 20-30, and 30-20 °C, where the third and fourth treatment groups were gradually changed from their starting temperature to their final temperature between days 10 and 14. Telomere length was measured, and it was found that length decreased with age and that fish exposed to the 20 °C treatment had significantly shorter telomeres than those that received the 30-20 °C treatment. Telomeric attrition with age agrees with results previously found in studies of telomeres; however, the variation in attrition with temperature was not simply predictable and may be the synergistic effects of temperature and some other factor.

Factors Associated with Veterinary Clinical Faculty Attrition.

PubMed

Furr, Martin

Faculty attrition and recruitment for veterinary clinical faculty positions have been reported as significant problems in veterinary medical education. To investigate the factors that may be important in veterinary clinical faculty retention, the perceptions and views of veterinary clinical academic faculty were determined using a web-distributed electronic survey. Responses were dichotomized by whether the respondent had or had not left an academic position and were analyzed for their association with faculty attrition. A total of 1,226 responses were recorded, and results demonstrated that factors other than compensation were associated with veterinary clinical faculty attrition, including departmental culture, work-life balance, and recognition and support of clinical medicine by the administration. Forty-four percent of respondents who had held a faculty appointment reported leaving academia either voluntarily or for non-voluntary reasons such as failure to achieve tenure, retirement, or having their position closed. Attention to correcting deficiencies in workplace culture and professional rewards could be a beneficial means by which to decrease the faculty attrition rates currently observed in clinical academic veterinary medicine.

Mathematics and Science Education Attrition, Retention, and Migration: A Study of Three Urban School Districts in the State of Texas

ERIC Educational Resources Information Center

Davis, Margaret Cheri

2013-01-01

Teacher attrition has far-reaching implications that contribute to the success of student performance at many different educational levels. Research indicates as many as 50% of public school teachers leave the profession within the first 5 years, and some suggest that as many as 20% to 30% leave teaching after the first year. Attrition is a…

Predictors of Attrition in the Finnish Conscript Service

DTIC Science & Technology

2006-11-01

characteristics like low self - esteem , a low frustration level, problems with authority, and high aggression have been more often found in those who attrit than...others (Dovrat, 1995). Similarly, the more a recruit has problems with morale, self -discipline, self - esteem , pride, and commitment, the less is his or her...diploma graduates have a decreased attrition risk (Hawes, 1990). Presumably, experiences at school such as social interaction, with self -discipline

The performance of sample selection estimators to control for attrition bias.

PubMed

Grasdal, A

2001-07-01

Sample attrition is a potential source of selection bias in experimental, as well as non-experimental programme evaluation. For labour market outcomes, such as employment status and earnings, missing data problems caused by attrition can be circumvented by the collection of follow-up data from administrative registers. For most non-labour market outcomes, however, investigators must rely on participants' willingness to co-operate in keeping detailed follow-up records and statistical correction procedures to identify and adjust for attrition bias. This paper combines survey and register data from a Norwegian randomized field trial to evaluate the performance of parametric and semi-parametric sample selection estimators commonly used to correct for attrition bias. The considered estimators work well in terms of producing point estimates of treatment effects close to the experimental benchmark estimates. Results are sensitive to exclusion restrictions. The analysis also demonstrates an inherent paradox in the 'common support' approach, which prescribes exclusion from the analysis of observations outside of common support for the selection probability. The more important treatment status is as a determinant of attrition, the larger is the proportion of treated with support for the selection probability outside the range, for which comparison with untreated counterparts is possible. Copyright 2001 John Wiley & Sons, Ltd.

Proximal attrition facets: morphometric, demographic, and aging characteristics.

PubMed

Sarig, Rachel; Hershkovitz, Israel; Shvalb, Nir; Sella-Tunis, Tatiana; May, Hila; Vardimon, Alexander D

2014-08-01

Although interproximal attrition is considered to be limited in modern populations, it has important clinical implications. However, in contrast to occlusal attrition, proximal attrition receives limited scientific attention. The main purpose of the current study was to fill this void. Seven-hundred and sixty-five teeth were collected from 255 skulls of subjects 18-75 yr of age. For each individual, three mandibular teeth (the first and second premolars and the first molar) were examined for proximal attrition facets (PAFs). The results provide detailed information on the size, shape, and location of the facets according to age cohort, gender, and ethnicity. The validity of the method used to measure the facets was also examined. The major findings were as follows: PAFs are usually located on the upper half of the crown proximal aspect; in each tooth, the mesial facet is more lingually positioned and the distal facet is more buccally positioned; the majority of the facets are subrectangular in shape; the size of the facets tends to increase in an anteroposterior direction (from premolars to molars); and facet size and location are age- and sex-dependent and ethnicity-independent. It is our recommendation that dentists bear in mind that interproximal attrition is a dynamic, long-term process and needs to be considered in many clinical scenarios. © 2014 Eur J Oral Sci.

Solid organ allograft survival improvement in the United States: the long-term does not mirror the dramatic short-term success.

PubMed

Lodhi, S A; Lamb, K E; Meier-Kriesche, H U

2011-06-01

Organ survival in the short-term period post-transplant has improved dramatically over the past few decades. Whether this has translated to a long-term survival benefit remains unclear. This study quantifies the progression of nonrenal solid organ transplant outcomes from 1989 to 2009 in liver, lung, heart, intestine and pancreas transplants. Long-term graft survival was analyzed using data on adult solid organ transplant recipients from the UNOS/SRTR database and is reported as organ half-life and yearly attrition rates. Liver, lung, heart, intestine and pancreas half-lives have improved from 5.8 to 8.5, 1.7 to 5.2, 8.8 to 11, 2.1 to 3.6 and 10.5 to 16.7 years, respectively. Long-term attrition rates have not shown the same consistent improvement, with the yearly attrition rate 5-10 years post-transplant for liver, lung, heart and pancreas changing from 4.7 to 4.3, 10.9 to 10.1, 6.4 to 5.1 and 3.3 to 4.2, respectively. Attrition rates for intestine and pancreas transplantation alone display more variability due to smaller sample size but exhibit similar trends of improved first-year attrition and relatively stagnant long-term attrition rates. With first-year survival and attrition rates almost at a pinnacle, further progress in long-term survival will come from targeting endpoints beyond first-year rejection and survival rates. ©2011 The Authors Journal compilation©2011 The American Society of Transplantation and the American Society of Transplant Surgeons.

Perceptions of Attrition and Family Participation: A Qualitative Study of Pediatric Obesity Clinicians

PubMed Central

Skelton, Joseph A.; Irby, Megan B.; Beech, Bettina M.; Rhodes, Scott D.

2012-01-01

Objective The majority of participants drop out of pediatric obesity treatment programs; however, clinicians have little knowledge of how to address this problem. The objective of this study was to explore obesity treatment clinicians’ perceptions of contributors to attrition, as well as methods to maintain family participation. Methods Semi-structured interviews were conducted with 29 pediatric obesity clinicians representing primary care (PC), community-based (CB), and tertiary-care (TC) treatment programs in North Carolina. Interviews were recorded, transcribed verbatim, and coded using a multistage inductive approach. Grounded theory was used to analyze responses. Results Eleven themes emerged from analysis, including: the influence of program elements, family characteristics, and the variety of approaches employed to address retention. Only TC programs reported attempts to address attrition. Patients’ past experiences with obesity treatment, desire for immediate outcomes, and relationships with clinicians were perceived as important factors related to attrition. Other important themes were: families’ understanding of obesity treatment; importance of realistic expectations; and families’ value of treatment. Important differences and similarities among programs were identified. All clinicians reported families came to treatment through physician-, not self-referral. Conclusions Clinicians perceive attrition to be a significant problem in pediatric obesity treatment. As a result of clinical interviews, several potential avenues to address attrition were identified, including: the need for clinicians to develop relationships with families, assist in building appropriate expectations, and address families’ value of treatment. Findings of this study can inform larger investigations of attrition, and guide exploration of family impressions of and experiences in treatment. PMID:22795203

Income differentials in functional disability in old age: relative risks of onset, recovery, decline, attrition and mortality.

PubMed

Broese van Groenou, Marjolein I; Deeg, Dorly J H; Penninx, Brenda W J H

2003-04-01

Socioeconomic status (SES) differences in health decline in late life may be underestimated, because the relatively higher risks of attrition of lower-SES persons are seldom taken into account. This longitudinal study aimed at comparing income differences in the course of disability, non-mortality attrition and mortality in older adults. A sample population of 3107 older adults who participated in the 1992/1993 baseline of the Longitudinal Aging Study Amsterdam was examined regarding changes in functional disability in 1998/1999. SES was indicated by household income. Multinomial regression analyses revealed that, for men without disability at baseline, the relative rate for attrition was four times higher and the mortality rate was twice as high for low-income vs high-income persons. For non-disabled women, the relative risk for the onset of disability was nearly twice as high for low-income vs high-income persons. For both men and women, these risks decreased only slightly when behavioral and psychosocial risk factors were taken into account. Among persons with disability at baseline, the relative risks for attrition (for women) and mortality (for men) were twice as high for low-income persons, but no income differences were found with respect to recovery and decline. Adjustment for risk factors decreased the relative risks for attrition and mortality to a non-significant level. Income inequality in health in late life is to a large degree explained by the higher incidence of disability among lower-status women and by the higher attrition and mortality risks among lower-status men.

Examining the Relationship Between Mental, Physical, and Organizational Factors Associated With Attrition During Maritime Forces Training.

PubMed

Binsch, Olaf; Banko, Katherine M; Veenstra, Bertil J; Valk, Pierre J L

2015-11-01

For infantry units of the Dutch Ministry of Defence, high attrition rates (varying from 42 to 68%) during initial training are a persisting problem. The reasons for this attrition are diverse. Having better insight into the causes of attrition is a prerequisite for implementing preventive measures. To achieve this, a monitoring assessment system was developed that integrated the effects of physical, mental, and organizational determinants on operational readiness. The aim of this study was to implement the monitoring tools and to establish the set of determinants that best predicted attrition during infantry training of new recruits. Eighty-five recruits were monitored over a 24-week infantry training course. Before the training, recruits were screened for medical, psychological, and physical wellness. During the monitoring phase, mental, physiological, and organizational indicants were obtained using an array of tools such as questionnaires, chest belt monitors (for heart rate, acceleration, and skin temperature measurements), and computerized tests (e.g., vigilance, long-term memory). Survival analyses were used to tease out the determinants of individual and grouped predictors of attrition. Nearly half the recruits (47%) failed the training. Attrition was predicted by both physiological and mental determinants. However, the organizational determinant "trainers' judgment" on the "recruits' military quality" dominated the physiological and mental determinants. It was concluded that the monitoring system was successfully implemented during infantry training, and that the survival analysis method emphasized on single effects and interactions between the different determinants. Based on the current findings, we recommend several steps to successfully implement a monitoring method in settings with high demands.

Baseline biopsychosocial determinants of telomere length and 6-year attrition rate.

PubMed

Révész, Dóra; Milaneschi, Yuri; Terpstra, Erik M; Penninx, Brenda W J H

2016-05-01

Short leukocyte telomere length (TL) and accelerated telomere attrition have been associated with various deleterious health outcomes, although their determinants have not been explored collectively in a large-scale study. Leukocyte TL was measured (baseline N=2936; 6-year follow-up N=1860) in participants (18-65 years) from the NESDA study. Baseline determinants of TL included sociodemographics, lifestyle, chronic diseases, psychosocial stressors, and metabolic and physiological stress markers. Multivariate linear regression models were used to examine the associations between these determinants and (1) baseline TL, and (2) 6-year TL change. Multinomial logistic regression analyses were used to examine the predictors of telomere attrition and lengthening, as compared to stable TL. Short baseline TL was associated with older age, male sex, non-European ethnicity, cigarette smoking, recent life events, and higher triglycerides, glucose and pre-ejection period (R(2)=11.3%). The 6-year telomere attrition was inversely associated with baseline TL (R(2)=51.6%); also older age, long sleep, not having a partner, high childhood trauma index, and gastrointestinal disease were associated with 6-year TL attrition (additional R(2)=3.7%). Telomere attrition seemed to have slightly more predictors than lengthening. Sociodemographic, lifestyle, psychosocial stress and metabolic and physiological stress factors are cross-sectionally linked with TL. Telomere attrition over six years was strongly associated with baseline TL, suggesting an internal homeostatic influence. Modulation of the identified determinants may become target of future studies to promote telomere maintenance and healthy aging. Copyright © 2016 Elsevier Ltd. All rights reserved.

Methods for Evaluating Respondent Attrition in Web-Based Surveys

PubMed Central

Sabo, Roy T; Krist, Alex H; Day, Teresa; Cyrus, John; Woolf, Steven H

2016-01-01

Background Electronic surveys are convenient, cost effective, and increasingly popular tools for collecting information. While the online platform allows researchers to recruit and enroll more participants, there is an increased risk of participant dropout in Web-based research. Often, these dropout trends are simply reported, adjusted for, or ignored altogether. Objective To propose a conceptual framework that analyzes respondent attrition and demonstrates the utility of these methods with existing survey data. Methods First, we suggest visualization of attrition trends using bar charts and survival curves. Next, we propose a generalized linear mixed model (GLMM) to detect or confirm significant attrition points. Finally, we suggest applications of existing statistical methods to investigate the effect of internal survey characteristics and patient characteristics on dropout. In order to apply this framework, we conducted a case study; a seventeen-item Informed Decision-Making (IDM) module addressing how and why patients make decisions about cancer screening. Results Using the framework, we were able to find significant attrition points at Questions 4, 6, 7, and 9, and were also able to identify participant responses and characteristics associated with dropout at these points and overall. Conclusions When these methods were applied to survey data, significant attrition trends were revealed, both visually and empirically, that can inspire researchers to investigate the factors associated with survey dropout, address whether survey completion is associated with health outcomes, and compare attrition patterns between groups. The framework can be used to extract information beyond simple responses, can be useful during survey development, and can help determine the external validity of survey results. PMID:27876687

The role of service readiness and health care facility factors in attrition from Option B+ in Haiti: a joint examination of electronic medical records and service provision assessment survey data.

PubMed

Lipira, Lauren; Kemp, Christopher; Domercant, Jean Wysler; Honoré, Jean Guy; Francois, Kesner; Puttkammer, Nancy

2018-01-01

Option B+ is a strategy wherein pregnant or breastfeeding women with HIV are enrolled in lifelong antiretroviral therapy (ART) for prevention of mother-to-child transmission (PMTCT) of HIV. In Haiti, attrition from Option B+ is problematic and variable across health care facilities. This study explores service readiness and other facility factors as predictors of Option B+ attrition in Haiti. This analysis used longitudinal data from 2012 to 2014 from the iSanté electronic medical record system and cross-sectional data from Haiti's 2013 Service Provision Assessment. Predictors included Service Availability and Readiness Assessment (SARA) measures for antenatal care (ANC), PMTCT, HIV care services and ART services; general facility characteristics and patient-level factors. Multivariable Cox proportional hazards models modelled the time to first attrition. Analysis of data from 3147 women at 63 health care facilities showed no significant relationships between SARA measures and attrition. Having integrated ANC/PMTCT care and HIV-related training were significant protective factors. Being a public-sector facility, having a greater number of quality improvement activities and training in ANC were significant risk factors. Several facility-level factors were associated with Option B+ attrition. Future research is needed to explore unmeasured facility factors, clarify causal relationships, and incorporate community-level factors into the analysis of Option B+ attrition. © The Author(s) 2018. Published by Oxford University Press on behalf of Royal Society of Tropical Medicine and Hygiene. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Attrition rates, reasons, and predictive factors in supportive care and palliative oncology clinical trials.

PubMed

Hui, David; Glitza, Isabella; Chisholm, Gary; Yennu, Sriram; Bruera, Eduardo

2013-03-01

Attrition is common among supportive care/palliative oncology clinical trials. However, to the authors' knowledge, few studies to date have documented the reasons and predictors for dropout. In the current study, the authors' objective was to determine the rate, reasons, and factors associated with attrition both before reaching the primary endpoint and at the end of the study. A review of all prospective interventional supportive care/palliative oncology trials conducted in the Department of Palliative Care and Rehabilitation Medicine at The University of Texas MD Anderson Cancer Center in Houston between 1999 and 2011 was performed. Patient and study characteristics and attrition data were extracted. A total of 1214 patients were included in 18 clinical trials. The median age of the patients was 60 years. Approximately 41% had an Eastern Cooperative Oncology Group performance status of ≥ 3, a median Edmonton Symptom Assessment Scale (ESAS) for fatigue of 7 of 10, and a median ESAS for dyspnea of 2 of 10. The attrition rate was 26% (95% confidence interval [95% CI], 23%-28%) for the primary endpoint and 44% (95% CI, 41%-47%) for the end of the study. Common reasons for primary endpoint dropout were symptom burden (21%), patient preference (15%), hospitalization (10%), and death (6%). Primary endpoint attrition was associated with a higher baseline intensity of fatigue (odds ratio [OR], 1.10 per point; P = .01) and a longer study duration (P = .04). End-of-study attrition was associated with higher baseline levels of dyspnea (OR, 1.06; P = .01), fatigue (OR, 1.08; P = .01), Hispanic race (OR, 1.87; P = .002), higher level of education (P = .02), longer study duration (P = .01), and outpatient studies (P = 0.05). The attrition rate was high in supportive care/palliative oncology clinical trials, and was associated with various patient characteristics and a high baseline symptom burden. These findings have implications for future clinical trial design including eligibility criteria and sample size calculation. Copyright © 2012 American Cancer Society.

Factors associated with general surgery residents' desire to leave residency programs: a multi-institutional study.

PubMed

Gifford, Edward; Galante, Joseph; Kaji, Amy H; Nguyen, Virginia; Nelson, M Timothy; Sidwell, Richard A; Hartranft, Thomas; Jarman, Benjamin; Melcher, Marc; Reeves, Mark; Reid, Christopher; Jacobsen, Garth R; Thompson, Jonathan; Are, Chandrakanth; Smith, Brian; Arnell, Tracey; Hines, Oscar J; de Virgilio, Christian

2014-09-01

General surgical residency continues to experience attrition. To date, work hour amendments have not changed the annual rate of attrition. To determine how often categorical general surgery residents seriously consider leaving residency. At 13 residency programs, an anonymous survey of 371 categorical general surgery residents and 10-year attrition rates for each program. Responses from those who seriously considered leaving surgical residency were compared with those who did not. Factors associated with the desire to leave residency. The survey response rate was 77.6%. Overall, 58.0% seriously considered leaving training. The most frequent reasons for wanting to leave were sleep deprivation on a specific rotation (50.0%), an undesirable future lifestyle (47.0%), and excessive work hours on a specific rotation (41.4%). Factors most often cited that kept residents from leaving were support from family or significant others (65.0%), support from other residents (63.5%), and perception of being better rested (58.9%). On univariate analysis, older age, female sex, postgraduate year, training in a university program, the presence of a faculty mentor, and lack of Alpha Omega Alpha status were associated with serious thoughts of leaving surgical residency. On multivariate analysis, only female sex was significantly associated with serious thoughts of leaving residency (odds ratio, 1.2; 95% CI, 1.1-1.3; P = .003). Eighty-six respondents were from historically high-attrition programs, and 202 respondents were from historically low-attrition programs (27.8% vs 8.4% 10-year attrition rate, P = .04). Residents from high-attrition programs were more likely to seriously consider leaving residency (odds ratio, 1.8; 95% CI, 1.0-3.0; P = .03). A majority of categorical general surgery residents seriously consider leaving residency. Female residents are more likely to consider leaving. Thoughts of leaving seem to be associated with work conditions on specific rotations rather than with overall work hours and are more prevalent among programs with historically high attrition rates.

Synthesis of sea urchin-like carbon nanotubes on nano-diamond powder.

PubMed

Hwang, E J; Lee, S K; Jeong, M G; Lee, Y B; Lim, D S

2012-07-01

Carbon nanotubes (CNTs) have unique atomic structure and properties, such as a high aspect ratio and high mechanical, electrical and thermal properties. On the other hand, the agglomeration and entanglement of CNTs restrict their applications. Sea urchin-like multiwalled carbon nanotubes, which have a small aspect ratio, can minimize the problem of dispersion. The high hardness, thermal conductivity and chemical inertness of the nano-diamond powder make it suitable for a wide range of applications in the mechanical and electronic fields. CNTs were synthesized on nano-diamond powder by thermal CVD to fabricate a filler with suitable mechanical properties and chemical stability. This paper reports the growth of CNTs with a sea urchin-like structure on the surface of the nano-diamond powder. Nano-diamond powders were dispersed in an attritional milling system using zirconia beads in ethanol. After the milling process, 3-aminopropyltrimethoxysilane (APS) was added as a linker. Silanization was performed between the nano-diamond particles and the metal catalyst. Iron chloride was used as a catalyst for the fabrication of the CNTs. After drying, catalyst-attached nano-diamond powders could be achieved. The growth of the carbon nanotubes was carried out by CVD. The CNT morphology was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mean diameter and length of the CNTs were 201 nm and 3.25 microm, respectively.

Fast Sealift and Maritime Prepositioning Options for Improving Sealift Capabilities

DTIC Science & Technology

1991-01-01

cargo ships with speeds of 22 to 25 knots as fas* The eight existing T- AKRs , which have a speed of 30... cargo than in the case of no ship attrition. 2.0 ---- Without -- attrition --- • attrition 0- 1.0- High -capacity Low-cost Improved MPS( A ) SES T- AKR ...fast sealift and maritime prepositioning ships and evaluates their performance in terms of speed and the ability to make cumulative cargo deliveries

First Language Attrition Induces Changes in Online Morphosyntactic Processing and Re-Analysis: An ERP Study of Number Agreement in Complex Italian Sentences

ERIC Educational Resources Information Center

Kasparian, Kristina; Vespignani, Francesco; Steinhauer, Karsten

2017-01-01

First language (L1) attrition in adulthood offers new insight on neuroplasticity and the role of language experience in shaping neurocognitive responses to language. Attriters are multilinguals for whom advancing L2 proficiency comes at the cost of the L1, as they experience a shift in exposure and dominance (e.g., due to immigration). To date,…

Exploratory Development Research of U.S. Navy Marine Corps Personnel, Phase 1. Factors Affecting Attrition

DTIC Science & Technology

1977-09-30

havior. He has taught courses in research and has had con- siderable experience in the design and analysis of qualitative and quantitative research...name, serial number, unit, rank, or other identifying information was asked. Research pesign The research design was developed to determine if causes of...attrition have similar impach on men in various situations. The design includes three principal components. First, both attriters and adjusted men

Pharmacotherapy for social anxiety disorder: Interpersonal predictors of outcome and the mediating role of the working alliance.

PubMed

Cohen, Jonah N; Drabick, Deborah A G; Blanco, Carlos; Schneier, Franklin R; Liebowitz, Michael R; Heimberg, Richard G

2017-12-01

Social anxiety disorder (SAD) is highly prevalent and associated with high levels of impairment and distress. Therapies for SAD leave many patients symptomatic at the end of treatment, and little is known about predictors or mechanisms of treatment outcome. Given the interpersonal dysfunction fundamental to SAD, this study investigated whether prominent interpersonal features of SAD (submissive behavior, childhood maltreatment, suppression of anger, and depression) predicted attrition and response to pharmacotherapy and whether the working alliance mediated these relationships. This is the first study to examine the role of the working alliance in pharmacotherapy for SAD. One hundred thirty-eight treatment-seeking individuals with a primary diagnosis of SAD received 12 weeks of open treatment with paroxetine. Higher levels of depression predicted greater severity of SAD at the end of treatment, and higher levels of submissive behavior and childhood emotional maltreatment predicted a greater probability of attrition from treatment. The psychiatrist-assessed working alliance mediated response to pharmacotherapy for individuals who reported a history of emotional maltreatment. These results identify variables that predict pharmacotherapy outcome and emphasize the importance of the working alliance as a mechanism of treatment response for those with a history of emotional maltreatment. Implications for person-specific treatment selection are discussed. Copyright © 2017 Elsevier Ltd. All rights reserved.

The mechanism of vapor phase hydration of calcium oxide: implications for CO2 capture.

PubMed

Kudłacz, Krzysztof; Rodriguez-Navarro, Carlos

2014-10-21

Lime-based sorbents are used for fuel- and flue-gas capture, thereby representing an economic and effective way to reduce CO2 emissions. Their use involves cyclic carbonation/calcination which results in a significant conversion reduction with increasing number of cycles. To reactivate spent CaO, vapor phase hydration is typically performed. However, little is known about the ultimate mechanism of such a hydration process. Here, we show that the vapor phase hydration of CaO formed after calcination of calcite (CaCO3) single crystals is a pseudomorphic, topotactic process, which progresses via an intermediate disordered phase prior to the final formation of oriented Ca(OH)2 nanocrystals. The strong structural control during this solid-state phase transition implies that the microstructural features of the CaO parent phase predetermine the final structural and physicochemical (reactivity and attrition) features of the product hydroxide. The higher molar volume of the product can create an impervious shell around unreacted CaO, thereby limiting the efficiency of the reactivation process. However, in the case of compact, sintered CaO structures, volume expansion cannot be accommodated in the reduced pore volume, and stress generation leads to pervasive cracking. This favors complete hydration but also detrimental attrition. Implications of these results in carbon capture and storage (CCS) are discussed.

MDR-TB screening in a setting with molecular diagnostic techniques: who got tested, who didn't and why?

PubMed Central

Govindarajan, S.; Sharath, B. N.; Tripathy, J. P.; Chinnakali, P.; Kumar, A. M. V.; Muthaiah, M.; Vivekananda, K.; Paulraj, A. K.; Roy, G.

2015-01-01

Setting: The Revised National Tuberculosis Control Programme, Puducherry, India, which has facilities for molecular diagnostic technique. Objective: To determine pre-diagnostic and pre-treatment attrition among presumptive multidrug-resistant tuberculosis (MDR-TB) patients and reasons for attrition. Methods: In this mixed-methods study, the quantitative component consisted of retrospective cohort analysis through record review of all presumptive MDR-TB patients recorded between October 2012 and September 2013. The qualitative component included in-depth interviews with key informants involved in programmatic management of drug-resistant tuberculosis services. Results: Of 341 eligible presumptive MDR-TB patients, pre-diagnostic and pre-treatment attrition was respectively 45.5% (155/341) and 29% (2/7). Patients with extra-pulmonary TB (RR = 2.3), those with human immuno-deficiency and TB co-infection (RR = 1.7), those registered during October–December 2012 (RR = 1.3) and those identified from primary/secondary health centres (RR = 1.8) were less likely to be tested. Themes that emerged during the analysis of the qualitative data were ‘lack of a systematic mechanism to track referrals for culture and drug susceptibility testing’, ‘absence of courier service to transport sputum’, ‘lack of knowledge and ownership among staff of general health system’, ‘shortage of diagnostic kits’ and ‘patient non-adherence’. Conclusion: Despite the introduction of molecular diagnostic techniques, operational issues in MDR-TB screening remain a concern and require urgent attention. PMID:26400385

A Qualitative Evaluation of Engagement and Attrition in a Nurse Home Visiting Program: From the Participant and Provider Perspective.

PubMed

Beasley, Lana O; Ridings, Leigh E; Smith, Tyler J; Shields, Jennifer D; Silovsky, Jane F; Beasley, William; Bard, David

2018-05-01

Beginning parenting programs in the prenatal and early postnatal periods have a large potential for impact on later child and maternal outcomes. Home-based parenting programs, such as the Nurse Family Partnership (NFP), have been established to help address this need. Program reach and impact is dependent on successful engagement of expecting mothers with significant risks; however, NFP attrition rates remain high. The current study qualitatively examined engagement and attrition from the perspectives of NFP nurses and mothers in order to identify mechanisms that enhance service engagement. Semi-structured interviews were conducted in focus groups composed of either engaged (27 total mothers) or unengaged (15 total mothers) mothers from the NFP program. NFP nurses (25 total nurses) were recruited for individual semi-structured interviews. Results suggest that understanding engagement in the NFP program requires addressing both initial and sustained engagement. Themes associated with enhanced initial engagement include nurse characteristics (e.g., flexible, supportive, caring) and establishment of a solid nurse-family relationship founded on these characteristics. Factors impacting sustained engagement include nurse characteristics, provision of educational materials on child development, individualized services for families, and available family support. Identified barriers to completing services include competing demands and lack of support. Findings of this study have direct relevance for workforce planning, including hiring and training through integrating results regarding effective nurse characteristics. Additional program supports to enhance parent engagement may be implemented across home-based parenting programs in light of the current study's findings.

Kinship and familiarity mitigate costs of social conflict between Seychelles warbler neighbors

PubMed Central

Fairfield, Eleanor A.; Komdeur, Jan; Spurgin, Lewis G.; Richardson, David S.

2017-01-01

Because virtually all organisms compete with others in their social environment, mechanisms that reduce conflict between interacting individuals are crucial for the evolution of stable families, groups, and societies. Here, we tested whether costs of social conflict over territorial space between Seychelles warblers (Acrocephalus sechellensis) are mitigated by kin-selected (genetic relatedness) or mutualistic (social familiarity) mechanisms. By measuring longitudinal changes in individuals’ body mass and telomere length, we demonstrated that the fitness costs of territoriality are driven by a complex interplay between relatedness, familiarity, local density, and sex. Physical fights were less common at territory boundaries shared between related or familiar males. In line with this, male territory owners gained mass when living next to related or familiar males and also showed less telomere attrition when living next to male kin. Importantly, these relationships were strongest in high-density areas of the population. Males also had more rapid telomere attrition when living next to unfamiliar male neighbors, but mainly when relatedness to those neighbors was also low. In contrast, neither kinship nor familiarity was linked to body mass or telomere loss in female territory owners. Our results indicate that resolving conflict over territorial space through kin-selected or mutualistic pathways can reduce both immediate energetic costs and permanent somatic damage, thus providing an important mechanism to explain fine-scale population structure and cooperation between different social units across a broad range of taxa. PMID:29073100

Grit: a marker of residents at risk for attrition?

PubMed

Burkhart, Richard A; Tholey, Renee M; Guinto, Donna; Yeo, Charles J; Chojnacki, Karen A

2014-06-01

Attrition from general surgery residency remains constant at approximately 20% despite nearly a decade of work-hour reform and studies aiming to identify common risk factors. High rates of attrition from training have a wide impact, from the overall quality of trainees produced to implications on public health and the broader surgical work force. We set out to evaluate a novel character trait, grit, defined as passion and perseverance for long-term goals, as a marker and potential risk factor for resident attrition. Twelve Accreditation Council for Graduate Medical Education-approved general surgery residency programs participated in a prospective, multi-institutional, survey-based analysis of grit and attrition during the 2012-2013 academic year. Participating individuals were blinded with regards to the primary outcome of the study. Participating institutions were blinded to the responses of their trainees. Participating residency programs were located in a variety of settings, from university-based health systems to community hospitals. Sixty-eight percent (68%) of residents (180 of 265) at participating institutions completed the study. The primary end point for this study was attrition from residency as a function of grit. Secondary end points included an evaluation of the utility of the grit score in surgical residents, variability of grit according to postgraduate year, sex, measurements of resident satisfaction with current program, lifestyle, and career goals. Finally, the study included an analysis of key resident support strategies. The attrition rate across 12 institutions surveyed was approximately 2% (5 residents). Of those five, three participated in our study. All three had below-median levels of grit. Those residents with below-median grit were more likely to contemplate leaving surgical residency. Given the low attrition rate, no variable surveyed reached statistical significance in our analysis. Key support strategies for residents responding included family, friends outside of residency, co-residents, and formal mentorship through their particular residency. In this preliminary underpowered study, grit appears to be a promising marker and risk factor for attrition from surgical residency. In an effort to retain residents, programs should consider screening for grit in current residents and directing support to those residents with below-median values, with a focus on building family, friend, and formal mentor relationships. Copyright © 2014 Mosby, Inc. All rights reserved.

Factors contributing to attrition behavior in diabetes self-management programs: A mixed method approach

PubMed Central

Gucciardi, Enza; DeMelo, Margaret; Offenheim, Ana; Stewart, Donna E

2008-01-01

Background Diabetes self-management education is a critical component in diabetes care. Despite worldwide efforts to develop efficacious DSME programs, high attrition rates are often reported in clinical practice. The objective of this study was to examine factors that may contribute to attrition behavior in diabetes self-management programs. Methods We conducted telephone interviews with individuals who had Type 2 diabetes (n = 267) and attended a diabetes education centre. Multivariable logistic regression was performed to identify factors associated with attrition behavior. Forty-four percent of participants (n = 118) withdrew prematurely from the program and were asked an open-ended question regarding their discontinuation of services. We used content analysis to code and generate themes, which were then organized under the Behavioral Model of Health Service Utilization. Results Working full and part-time, being over 65 years of age, having a regular primary care physician or fewer diabetes symptoms were contributing factors to attrition behaviour in our multivariable logistic regression. The most common reasons given by participants for attrition from the program were conflict between their work schedules and the centre's hours of operation, patients' confidence in their own knowledge and ability when managing their diabetes, apathy towards diabetes education, distance to the centre, forgetfulness, regular physician consultation, low perceived seriousness of diabetes, and lack of familiarity with the centre and its services. There was considerable overlap between our quantitative and qualitative results. Conclusion Reducing attrition behaviour requires a range of strategies targeted towards delivering convenient and accessible services, familiarizing individuals with these services, increasing communication between centres and their patients, and creating better partnerships between centres and primary care physicians. PMID:18248673

Methods for Evaluating Respondent Attrition in Web-Based Surveys.

PubMed

Hochheimer, Camille J; Sabo, Roy T; Krist, Alex H; Day, Teresa; Cyrus, John; Woolf, Steven H

2016-11-22

Electronic surveys are convenient, cost effective, and increasingly popular tools for collecting information. While the online platform allows researchers to recruit and enroll more participants, there is an increased risk of participant dropout in Web-based research. Often, these dropout trends are simply reported, adjusted for, or ignored altogether. To propose a conceptual framework that analyzes respondent attrition and demonstrates the utility of these methods with existing survey data. First, we suggest visualization of attrition trends using bar charts and survival curves. Next, we propose a generalized linear mixed model (GLMM) to detect or confirm significant attrition points. Finally, we suggest applications of existing statistical methods to investigate the effect of internal survey characteristics and patient characteristics on dropout. In order to apply this framework, we conducted a case study; a seventeen-item Informed Decision-Making (IDM) module addressing how and why patients make decisions about cancer screening. Using the framework, we were able to find significant attrition points at Questions 4, 6, 7, and 9, and were also able to identify participant responses and characteristics associated with dropout at these points and overall. When these methods were applied to survey data, significant attrition trends were revealed, both visually and empirically, that can inspire researchers to investigate the factors associated with survey dropout, address whether survey completion is associated with health outcomes, and compare attrition patterns between groups. The framework can be used to extract information beyond simple responses, can be useful during survey development, and can help determine the external validity of survey results. ©Camille J Hochheimer, Roy T Sabo, Alex H Krist, Teresa Day, John Cyrus, Steven H Woolf. Originally published in the Journal of Medical Internet Research (http://www.jmir.org), 22.11.2016.

Patient attrition from the HIV antiretroviral therapy program at two hospitals in Haiti.

PubMed

Puttkammer, Nancy H; Zeliadt, Steven B; Baseman, Janet G; Destiné, Rodney; Wysler Domerçant, Jean; Labbé Coq, Nancy Rachel; Atwood Raphael, Nernst; Sherr, Kenneth; Tegger, Mary; Yuhas, Krista; Barnhart, Scott

2014-10-01

To identify factors associated with antiretroviral therapy (ART) attrition among patients initiating therapy in 2005-2011 at two large, public-sector department-level hospitals, and to inform interventions to improve ART retention. This retrospective cohort study used data from the iSanté electronic medical record (EMR) system. The study characterized ART attrition levels and explored the patient demographic, clinical, temporal, and service utilization factors associated with ART attrition, using time-to-event analysis methods. Among the 2 023 patients in the study, ART attrition on average was 17.0 per 100 person-years (95% confidence interval (CI): 15.8-18.3). In adjusted analyses, risk of ART attrition was up to 89% higher for patients living in distant communes compared to patients living in the same commune as the hospital (hazard ratio: 1.89, 95%CI: 1.54-2.33; P < 0.001). Hospital site, earlier year of ART start, spending less time enrolled in HIV care prior to ART initiation, receiving a non-standard ART regimen, lacking counseling prior to ART initiation, and having a higher body mass index were also associated with attrition risk. The findings suggest quality improvement interventions at the two hospitals, including: enhanced retention support and transportation subsidies for patients accessing care from remote areas; counseling for all patients prior to ART initiation; timely outreach to patients who miss ART pick-ups; "bridging services" for patients transferring care to alternative facilities; routine screening for anticipated interruptions in future ART pick-ups; and medical case review for patients placed on non-standard ART regimens. The findings are also relevant for policymaking on decentralization of ART services in Haiti.

Patient attrition from the HIV antiretroviral therapy program at two hospitals in Haiti

PubMed Central

Puttkammer, Nancy H.; Zeliadt, Steven B.; Baseman, Janet G.; Destiné, Rodney; Domerçant, Jean Wysler; Coq, Nancy Rachel Labbé; Raphael, Nernst Atwood; Sherr, Kenneth; Tegger, Mary; Yuhas, Krista; Barnhart, Scott

2016-01-01

Objective To identify factors associated with antiretroviral therapy (ART) attrition among patients initiating therapy in 2005–2011 at two large, public-sector department-level hospitals, and to inform interventions to improve ART retention. Methods This retrospective cohort study used data from the iSanté electronic medical record (EMR) system. The study characterized ART attrition levels and explored the patient demographic, clinical, temporal, and service utilization factors associated with ART attrition, using time-to-event analysis methods. Results Among the 2 023 patients in the study, ART attrition on average was 17.0 per 100 person-years (95% confidence interval (CI): 15.8–18.3). In adjusted analyses, risk of ART attrition was up to 89% higher for patients living in distant communes compared to patients living in the same commune as the hospital (hazard ratio: 1.89, 95%CI: 1.54–2.33; P < 0.001). Hospital site, earlier year of ART start, spending less time enrolled in HIV care prior to ART initiation, receiving a non-standard ART regimen, lacking counseling prior to ART initiation, and having a higher body mass index were also associated with attrition risk. Conclusions The findings suggest quality improvement interventions at the two hospitals, including: enhanced retention support and transportation subsidies for patients accessing care from remote areas; counseling for all patients prior to ART initiation; timely outreach to patients who miss ART pick-ups; “bridging services” for patients transferring care to alternative facilities; routine screening for anticipated interruptions in future ART pick-ups; and medical case review for patients placed on non-standard ART regimens. The findings are also relevant for policymaking on decentralization of ART services in Haiti. PMID:25563149

Why students leave in the UK: an integrative review of the international research literature.

PubMed

Cameron, Joan; Roxburgh, Michelle; Taylor, Julie; Lauder, William

2011-04-01

The purpose of this integrative review of the literature was to find and review international research studies that explored student attrition to determine what is known about the topic and to identify gaps in the research with a view to addressing the situation in the UK. Attrition from nursing programmes is a serious problem in the UK. It is recognised as a complex phenomenon, not attributable to a single cause. Regardless of actual attrition rates and trends, departments of nursing are challenged to perform in a business-like manner. Consequently, every student lost to a programme of study equates to a financial penalty for the department and to the future workforce and community.   Integrative review of the literature. Using electronic databases and specific search terms, 18 articles were identified and reviewed. Findings from the identified international research literature were analysed using qualitative content analysis. Four broad themes that accounted for factors of relevance to attrition were identified: Social, Prediction, Programme and Personal. Retention studies are fraught with methodological problems. These include incomplete or inaccurate data and low response rates. Attrition early in programmes may be attributed to a failure to understand the roles of nurses in contemporary societies. This has led to dissatisfaction with programmes and academic failure, as students may underestimate the intellectual demands of their programmes. Attrition later in the programme may be attributed to a combination of personal factors that culminate in a personal crisis. The research literature suggests that stereotyping of nurses is a major factor in attrition. Both professions need to find ways of communicating contemporary roles to wider society. © 2010 Blackwell Publishing Ltd.

Taking into account the impact of attrition on the assessment of response shift and true change: a multigroup structural equation modeling approach.

PubMed

Verdam, Mathilde G E; Oort, Frans J; van der Linden, Yvette M; Sprangers, Mirjam A G

2015-03-01

Missing data due to attrition present a challenge for the assessment and interpretation of change and response shift in HRQL outcomes. The objective was to handle such missingness and to assess response shift and 'true change' with the use of an attrition-based multigroup structural equation modeling (SEM) approach. Functional limitations and health impairments were measured in 1,157 cancer patients, who were treated with palliative radiotherapy for painful bone metastases, before [time (T) 0], every week after treatment (T1 through T12), and then monthly for up to 2 years (T13 through T24). To handle missing data due to attrition, the SEM procedure was extended to a multigroup approach, in which we distinguished three groups: short survival (3-5 measurements), medium survival (6-12 measurements), and long survival (>12 measurements). Attrition after third, sixth, and 13th measurement occasions was 11, 24, and 41 %, respectively. Results show that patterns of change in functional limitations and health impairments differ between patients with short, medium, or long survival. Moreover, three response-shift effects were detected: recalibration of 'pain' and 'sickness' and reprioritization of 'physical functioning.' If response-shift effects would not have been taken into account, functional limitations and health impairments would generally be underestimated across measurements. The multigroup SEM approach enables the analysis of data from patients with different patterns of missing data due to attrition. This approach does not only allow for detection of response shift and assessment of true change across measurements, but also allow for detection of differences in response shift and true change across groups of patients with different attrition rates.

Analysis of Special Forces Medic (18D) Attrition

DTIC Science & Technology

1994-08-01

130 students per year, 18D should reach 100% strength in the second quarter of FY95. Training Issues The biggest single reason for the high attrition...including a library and 24-hour study rooms, ix SOMED and SOMTC should consider incorporating computer-based training into the 18D training. The PA...particularly in the sciences. Given this, the high SOMED attrition rate is to be expected. Some have suggested that a greater effort should be made to recruit

Optimizing removal of arsenic, chromium, copper, pentachlorophenol and polychlorodibenzo-dioxins/furans from the 1-4 mm fraction of polluted soil using an attrition process.

PubMed

Guemiza, Karima; Coudert, Lucie; Tran, Lan Huong; Metahni, Sabrine; Blais, Jean-François; Besner, Simon; Mercier, Guy

2017-08-01

The objective of this study was to evaluate, at a pilot scale, the performance of an attrition process for removing As, Cr, Cu, pentachlorophenol (PCP) and polychlorodibenzodioxins and furans (PCDDF) from a 1-4 mm soil fraction. A Box-Behnken experimental design was utilized to evaluate the influence of several parameters (temperature, surfactant concentration and pulp density) and to optimize the main operating parameters of this attrition process. According to the results, the concentration of surfactant (cocamidopropylbetaine-BW) was the main parameter influencing both PCP and PCDDF removal from the 1-4 mm soil fraction by attrition. The behavior of each 2,3,7,8-PCDD/F congener during the attrition process was studied. The results indicated that the concentration of surfactant had a significant and positive effect on the removal of almost all of the dioxin and furan. The removal of 56%, 55%, 50%, 67% and 62% of the contaminants were obtained for As, Cr, Cu, PCP and PCDDF, respectively, using the optimized conditions ([BW]= 2% (w.w-1), T = 25°C and PD = 40% (w.w-1)). These results showed that attrition in the presence of a surfactant can be efficiently used to remediate the coarse fractions of soil contaminated by As, Cr, Cu, PCP and PCDDF.

Rate and pattern of interproximal dental attrition.

PubMed

Sarig, Rachel; Hershkovitz, Israel; Shpack, Nir; May, Hila; Vardimon, Alexander D

2015-08-01

Although occlusal and interproximal attrition occur because of diverse etiology and present dissimilar features, both progress with age. The objectives of this study were to reveal the rate and pattern of development of interproximal attrition facets (PAF) with age and to compare those with occlusal attrition (OA) changes. Five-hundred and ninety-four teeth were collected from 198 skulls (of adults, 20-71 yr of age). Three mandibular teeth [first premolar (P1), second premolar (P2), and first molar (M1)] were examined for PAF size and OA rate. Interproximal attrition and OA followed similar patterns of development until subjects reached 40-45 yr of age, after which they took different paths: PAF did not increase in size and were not as large as in younger groups, regardless of facet location, whereas OA continued to progress. The PAF changes with age differed between premolars and molars, unlike OA, which presented a similar rate for all teeth studied. Although OA scores presented significantly moderate correlations with age, PAF area size demonstrated low correlations with age. Low, but significant, correlations were found between the rate of OA and that of PAF. However, PAF and OA exhibited different patterns of development with age. Premolars and molars presented dissimilar development of PAF, which is probably caused by a unique attrition pattern in the molar teeth, different morphology, and force vectors. © 2015 Eur J Oral Sci.

Determining Tooth Occlusal Surface Relief Indicator by Means of Automated 3d Shape Analysis

NASA Astrophysics Data System (ADS)

Gaboutchian, A. V.; Knyaz, V. A.

2017-05-01

Determining occlusal surface relief indicator plays an important role in odontometric tooth shape analysis. An analysis of the parameters of surface relief indicators provides valuable information about closure of dental arches (occlusion) and changes in structure of teeth in lifetime. Such data is relevant for dentistry or anthropology applications. Descriptive techniques commonly used for surface relief evaluation have limited precision which, as a result, does not provide for reliability of conclusions about structure and functioning of teeth. Parametric techniques developed for such applications need special facilities and are time-consuming which limits their spread and ease to access. Nevertheless the use of 3D models, obtained by photogrammetric techniques, allows attaining required measurements accuracy and has a potential for process automation. We introduce new approaches for determining tooth occlusal surface relief indicator and provide data on efficiency in use of different indicators in natural attrition evaluation.

Influence of delivery strategy on message-processing mechanisms and future adherence to a Dutch computer-tailored smoking cessation intervention.

PubMed

Stanczyk, Nicola Esther; Crutzen, Rik; Bolman, Catherine; Muris, Jean; de Vries, Hein

2013-02-06

Smoking tobacco is one of the most preventable causes of illness and death. Web-based tailored smoking cessation interventions have shown to be effective. Although these interventions have the potential to reach a large number of smokers, they often face high attrition rates, especially among lower educated smokers. A possible reason for the high attrition rates in the latter group is that computer-tailored smoking cessation interventions may not be attractive enough as they are mainly text-based. Video-based messages might be more effective in attracting attention and stimulating comprehension in people with a lower educational level and could therefore reduce attrition rates. The objective of the present study was to investigate whether differences exist in message-processing mechanisms (attention, comprehension, self-reference, appreciation, processing) and future adherence (intention to visit/use the website again, recommend the website to others), according to delivery strategy (video or text based messages) and educational level, to a Dutch computer-tailored smoking cessation program. Smokers who were motivated to quit within the following 6 months and who were aged over 16 were included in the program. Participants were randomly assigned to one of two conditions (video/text CT). The sample was stratified into 2 categories: lower and higher educated participants. In total, 139 participants completed the first session of the web-based tailored intervention and were subsequently asked to fill out a questionnaire assessing message-processing mechanisms and future adherence. ANOVAs and regression analyses were conducted to investigate the differences in message-processing mechanisms and future adherence with regard to delivery strategy and education. No interaction effects were found between delivery strategy (video vs text) and educational level on message-processing mechanisms and future adherence. Delivery strategy had no effect on future adherence and processing mechanisms. However, in both groups results indicated that lower educated participants showed higher attention (F(1,138)=3.97; P=.05) and processing levels (F(1,138)=4.58; P=.04). Results revealed also that lower educated participants were more inclined to visit the computer-tailored intervention website again (F(1,138)=4.43; P=.04). Computer-tailored programs have the potential to positively influence lower educated groups as they might be more involved in the computer-tailored intervention than higher educated smokers. Longitudinal studies with a larger sample are needed to gain more insight into the role of delivery strategy in tailored information and to investigate whether the intention to visit the intervention website again results in the ultimate goal of behavior change. Netherlands Trial Register (NTR3102).

Influence of Delivery Strategy on Message-Processing Mechanisms and Future Adherence to a Dutch Computer-Tailored Smoking Cessation Intervention

PubMed Central

Crutzen, Rik; Bolman, Catherine; Muris, Jean; de Vries, Hein

2013-01-01

Background Smoking tobacco is one of the most preventable causes of illness and death. Web-based tailored smoking cessation interventions have shown to be effective. Although these interventions have the potential to reach a large number of smokers, they often face high attrition rates, especially among lower educated smokers. A possible reason for the high attrition rates in the latter group is that computer-tailored smoking cessation interventions may not be attractive enough as they are mainly text-based. Video-based messages might be more effective in attracting attention and stimulating comprehension in people with a lower educational level and could therefore reduce attrition rates. Objective The objective of the present study was to investigate whether differences exist in message-processing mechanisms (attention, comprehension, self-reference, appreciation, processing) and future adherence (intention to visit/use the website again, recommend the website to others), according to delivery strategy (video or text based messages) and educational level, to a Dutch computer-tailored smoking cessation program. Methods Smokers who were motivated to quit within the following 6 months and who were aged over 16 were included in the program. Participants were randomly assigned to one of two conditions (video/text CT). The sample was stratified into 2 categories: lower and higher educated participants. In total, 139 participants completed the first session of the web-based tailored intervention and were subsequently asked to fill out a questionnaire assessing message-processing mechanisms and future adherence. ANOVAs and regression analyses were conducted to investigate the differences in message-processing mechanisms and future adherence with regard to delivery strategy and education. Results No interaction effects were found between delivery strategy (video vs text) and educational level on message-processing mechanisms and future adherence. Delivery strategy had no effect on future adherence and processing mechanisms. However, in both groups results indicated that lower educated participants showed higher attention (F 1,138=3.97; P=.05) and processing levels (F 1,138=4.58; P=.04). Results revealed also that lower educated participants were more inclined to visit the computer-tailored intervention website again (F 1,138=4.43; P=.04). Conclusions Computer-tailored programs have the potential to positively influence lower educated groups as they might be more involved in the computer-tailored intervention than higher educated smokers. Longitudinal studies with a larger sample are needed to gain more insight into the role of delivery strategy in tailored information and to investigate whether the intention to visit the intervention website again results in the ultimate goal of behavior change. Trial Registration Netherlands Trial Register (NTR3102). PMID:23388554

Elastomeric optical fiber sensors and method for detecting and measuring events occurring in elastic materials

DOEpatents

Muhs, Jeffrey D.; Capps, Gary J.; Smith, David B.; White, Clifford P.

1994-01-01

Fiber optic sensing means for the detection and measurement of events such as dynamic loadings imposed upon elastic materials including cementitious materials, elastomers, and animal body components and/or the attrition of such elastic materials are provided. One or more optical fibers each having a deformable core and cladding formed of an elastomeric material such as silicone rubber are embedded in the elastic material. Changes in light transmission through any of the optical fibers due the deformation of the optical fiber by the application of dynamic loads such as compression, tension, or bending loadings imposed on the elastic material or by the attrition of the elastic material such as by cracking, deterioration, aggregate break-up, and muscle, tendon, or organ atrophy provide a measurement of the dynamic loadings and attrition. The fiber optic sensors can be embedded in elastomers subject to dynamic loadings and attrition such as commonly used automobiles and in shoes for determining the amount and frequency of the dynamic loadings and the extent of attrition. The fiber optic sensors are also useable in cementitious material for determining the maturation thereof.

Prevalence of dental attrition in in vitro fertilization children of West Bengal.

PubMed

Kar, Sudipta; Sarkar, Subrata; Mukherjee, Ananya

2014-01-01

Dental attrition is one of the problems affecting the tooth structure. It may affect both in vitro fertilization (IVF) and spontaneously conceived children. This study was aimed to evaluate and to compare the prevalence of dental attrition in deciduous dentition of IVF and spontaneously conceived children. In a cross-sectional case control study dental attrition status of 3-5 years old children were assessed. The case group consisted of term, singleton babies who were the outcome of IVF in the studied area in 2009. The control group consisted of term, first child, singleton and spontaneously conceived 3-5 years old children who were also resident of the studied area. A sample of 153 IVF and 153 spontaneously conceived children was examined according to Hansson and Nilner classification. Statistical analysis was carried out using Chi-square tests (χ(2) ) or Z test. No statistically significant difference found in studied (IVF children) and control group (spontaneously conceived children). IVF children are considered same as spontaneously conceived children when studied in relation to dental attrition status.

The influence of temperature on limestone sulfation and attrition under fluidized bed combustion conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Montagnaro, Fabio; Salatino, Piero; Dipartimento di Ingegneria Chimica - Universita degli Studi di Napoli Federico II, Piazzale Vincenzo Tecchio 80, 80125 Napoli

2010-04-15

The influence of temperature on attrition of two limestones during desulfurization in a fluidized bed reactor was investigated. Differences in the microstructure of the two limestones were reflected by a different thickness of the sulfate shell formed upon sulfation and by a different value of the ultimate calcium conversion degree. Particle attrition and fragmentation were fairly small under moderately bubbling fluidization conditions for both limestones. An increase of temperature from 850 C to 900 C led to an increase of the attrition rate, most likely because of a particle weakening effect caused by a faster CO{sub 2} evolution during calcination.more » This weakening effect, however, was not sufficiently strong to enhance particle fragmentation in the bed. The progress of sulfation, associated to the build-up of a hard sulfate shell around the particles, led in any case to a decrease of the extent of attrition. Sulfation at 900 C was less effective than at 850 C, and this was shown to be related to the porosimetric features of the different samples. (author)« less

Pregnancy-related attrition in general surgery.

PubMed

Brown, Erin G; Galante, Joseph M; Keller, Benjamin A; Braxton, Juanita; Farmer, Diana L

2014-09-01

Residency attrition rates remain a great challenge for general surgery training programs. Despite the increasing acceptance of pregnancy during training, 1 common perception is that women who become pregnant are at increased risk of leaving surgery programs. To determine whether child rearing increases the risk of attrition from general surgery residency. Retrospective review of all categorical general surgery residents in a single academic general surgery residency program over a 10-year period. All categorical general surgery residents matriculated from July 1, 1999, until July 1, 2009. Voluntary attrition rate, involuntary attrition rate, and incidence of child rearing among residents. Eighty-five residents matched into categorical general surgery postgraduate year 1 spots from July 1, 1999, to July 1, 2009. Of the total residents, 49 (58%) were men while 36 (42%) were women. Attrition in the program was 18.8% (16 of 85). Seven (44%) of the residents who left the program were women; this was 19% of all female residents in the program. This was not significantly different from the proportion of men who left the program (P = .90). A higher percentage of women (57%) left after their intern year compared with men (22%). Furthermore, men had the highest rate of attrition during research (33%) while no women left during research years. Among the 85 residents, 9 women reported a total of 10 pregnancies and 16 men reported raising 21 children (1 woman and 1 man left the program). The proportion of child rearing was higher in those who did not leave the program but this did not reach significance (P = .10). Neither age (odds ratio, 1.0; 95% CI, 0.8-1.4), sex (odds ratio, 1.0; 95% CI, 0.2-3.6), nor incidence of child rearing during training (odds ratio, 1.0; 95% CI, 0.1-9.6) were associated with an increased risk of attrition. Residents with children born during training did not demonstrate fewer total case numbers (men, P = .40; women, P = .93) or board pass rates (men, P = .76; women, P = .50) compared with residents who did not have children during training. Women who had children during training were more likely to pursue fellowship (87.5%) than those who did not (66.7%)(P < .001). The current study demonstrated there was no association between female sex and attrition at our institution. Child rearing did not appear to be a risk factor for attrition in either men or women. Furthermore, child rearing did not negatively impact the quality of training based on case numbers and board pass rates. Despite prevalent stereotypes, child rearing did not cause women or men to leave the program.

The ins and outs of an online bipolar education program: a study of program attrition.

PubMed

Nicholas, Jennifer; Proudfoot, Judith; Parker, Gordon; Gillis, Inika; Burckhardt, Rowan; Manicavasagar, Vijaya; Smith, Meg

2010-12-19

The science of eHealth interventions is rapidly evolving. However, despite positive outcomes, evaluations of eHealth applications have thus far failed to explain the high attrition rates that are associated with some eHealth programs. Patient adherence remains an issue, and the science of attrition is still in its infancy. To our knowledge, there has been no in-depth qualitative study aimed at identifying the reasons for nonadherence to-and attrition from- online interventions. This paper explores the predictors of attrition and participant-reported reasons for nonadherence to an online psycho-education program for people newly diagnosed with a bipolar disorder. As part of an ongoing randomized controlled trial (RCT) evaluating an online psycho-education program for people newly diagnosed with a bipolar disorder, we undertook an in-depth qualitative study to identify participants' reasons for nonadherence to, and attrition from, the online intervention as well as a quantitative study investigating predictors of attrition. Within the RCT, 370 participants were randomly allocated to 1 of 2 active interventions or an attention control condition. Descriptive analyses and chi-square tests were used to explore the completion rates of 358 participants, and standard regression analysis was used to identify predictors of attrition. The data from interviews with a subsample of 39 participants who did not complete the online program were analyzed using "thematic analysis" to identify patterns in reported reasons for attrition. Overall, 26.5% of the sample did not complete their assigned intervention. Standard multiple regression analysis revealed that young age (P= .004), male gender (P= .001), and clinical recruitment setting (P= .001) were significant predictors of attrition (F(7,330)= 8.08, P< .001). Thematic analysis of interview data from the noncompleter subsample revealed that difficulties associated with the acute phases of bipolar disorder, not wanting to think about one's illness, and program factors such as the information being too general and not personally tailored were the major reasons for nonadherence. The dropout rate was equivalent to other Internet interventions and to face-to-face therapy. Findings from our qualitative study provide participant-reported reasons for discontinuing the online intervention, which, in conjunction with the quantitative investigations about predictors, add to understanding about Internet interventions. However, further research is needed to determine whether there are systematic differences between those who complete and those who do not complete eHealth interventions. Ultimately, this may lead to the identification of population subgroups that most benefit from eHealth interventions and to informing the development of strategies to improve adherence. ACTRN12608000411347; http://www.anzctr.org.au/ACTRN12608000411347.aspx (Archived by WebCite at http://www.webcitation.org/5uX4uYwVN).

Hydrogen sorption characteristics of nanostructured Pd–10Rh processed by cryomilling

DOE PAGES

Yang, Nancy; Yee, Joshua K.; Zhang, Zhihui; ...

2014-10-03

Palladium and its alloys are model systems for studying solid-state storage of hydrogen. Mechanical milling is commonly used to process complex powder systems for solid-state hydrogen storage; however, milling can also be used to evolve nanostructured powder to modify hydrogen sorption characteristics. In the present study, cryomilling (mechanical attrition milling in a cryogenic liquid) is used to produce nanostructured palladium-rhodium alloy powder. Characterization of the cryomilled Pd-10Rh using electron microscopy, X-ray diffraction, and surface area analysis reveals that (i) particle morphology evolves from spherical to flattened disk-like particles; while the (ii) crystallite size decreases from several microns to less thanmore » 100 nm and (iii) dislocation density increases with increased cryomilling time. Hydrogen absorption and desorption isotherms as well as the time scales for absorption were measured for cryomilled Pd-10Rh, and correlated with observed microstructural changes induced by the cryomilling process. In short, as the microstructure of the Pd-10Rh alloy is refined by cryomilling: (i) the maximum hydrogen concentration in the α-phase increases, (ii) the pressure plateau becomes flatter, and (iii) the equilibrium hydrogen capacity at 760 Torr increases. In addition, the rate of hydrogen absorption was reduced by an order of magnitude compared to non-cryomilled (atomized) powder.« less

Psychological and Organizational Factors Related to Attrition and Performance in Marine Corps Recruit Training

DTIC Science & Technology

1979-11-21

neceessary ad Identify by block number) Attrition, performance, organizational effectiveness, birth order , training units. 20. ABSTRACT (C’!!nue an reverse...reasons) and birth order (attrition rates were 6.0",, for oldest, 13.3’, for middle, and 18.8"t’ for youngest) on the personal/demoQraphic dimensiois. With...size, education level, race, family background, birth order , ratings of the quality of home life ai.d of school experiences, and aptitude measures

The Role of Personality Type on Minority Attrition at the US Naval Academy

DTIC Science & Technology

2002-06-01

Provost as more likely to attrite were ISTP, ESTP, ISFP, and ENFJ . “These students tend to be less organized, more passive in their relationship to...MBTI ISTP ISTJ ISFP ISFJ INTP INTJ INFP INFJ ESTP ESTJ ESFP ESFJ ENTP ENTJ ENFP ENFJ C ou nt 400 300 200 100 0 33 Table 12: Minority Attrition...reason to believe that all who are admitted have the potential to graduate. B. PURPOSE OF STUDY This thesis examines the relationship

Impact of Scheduled Attrition Rates on Meeting Monthly Sortie Goals in United States Air Force Bomb Wings

DTIC Science & Technology

2009-06-12

predict future losses in the monthly flying schedules. The purpose of the attrition is to ensure that units meet their sortie contract consistently. In...an era of decreasing force size, it is important for units to maximize aircrew training operations, without wasting manpower and resources. Thus, the ...primary research question is as follows: Is the current USAF scheduling technique of using a 5-year historical attrition rate an effective way to

Highly attrition-resistant zinc oxide-based sorbents for H{sub 2}S removal by spray-drying technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, J.B.; Baek, J.I.; Ryu, C.K.

2008-07-15

A ZnO-based sorbent, ZAC 32N, applicable to transport reactors was successfully prepared by the spray-drying technique. Another sorbent, ZAC 32SU, was prepared by scale-up preparation of ZAC 32N sorbent. The physical properties of the sorbents such as attrition resistance, specific surface area, pore volume, and particle size were extensively characterized and exhibited a good potential for use in transport applications. The chemical reactivity tested in the thermogravimetric analyzer and microreactor exhibited desirable characteristics for effective desulfurization of syngas streams in the range of 450-550{sup o}C. Bench-scale tests for the sorbent ZAC 32SU were performed for a continuous 160 h withmore » a steady solid circulation of 54.6 kg/h. The results showed 99.5%+ desulfurization at 500-550{sup o}C and reasonable regenerability at 550-620{sup o}C. Test results on the physical properties and chemical reactivity indicated that the performance of developed sorbents proved to be outstanding.« less

76 FR 2727 - Proposed Collection of Information

Federal Register 2010, 2011, 2012, 2013, 2014

2011-01-14

... attrition, as well as what information or education needs would increase the conversion ratio. An online... description of collection: To understand which factors are driving recruitment attrition, as well as what...

The singing/acting mature adult--singing instruction perspective.

PubMed

Westerman Gregg, J

1997-06-01

Complete knowledge of anatomy and physiology of the vocal mechanism and tract is essential for the voice teacher to be maximally effective. Possible contributing factors to vocal attrition in the mature singer/actor are outlined: poor posture, inadequate respiratory function, lack of adequate hydration, phonatory hyperfunction, habitual speaking pitch at too low a frequency, lack of resonance, tongue tension affecting phonation, resonation, and articulation. Techniques for rehabilitation of the damaged voice are recommended.

45 CFR 1356.84 - Sampling.

Code of Federal Regulations, 2012 CFR

2012-10-01

... Correction (FPC). The State agency must increase the resulting number by 30 percent to allow for attrition... 30 percent to allow for attrition, but the sample size must not be larger than the number of youth...

45 CFR 1356.84 - Sampling.

Code of Federal Regulations, 2013 CFR

2013-10-01

... Correction (FPC). The State agency must increase the resulting number by 30 percent to allow for attrition... 30 percent to allow for attrition, but the sample size must not be larger than the number of youth...

45 CFR 1356.84 - Sampling.

Code of Federal Regulations, 2014 CFR

2014-10-01

... Correction (FPC). The State agency must increase the resulting number by 30 percent to allow for attrition... 30 percent to allow for attrition, but the sample size must not be larger than the number of youth...

The implications of selective attrition for estimates of intergenerational elasticity of family income

PubMed Central

Schoeni, Robert F.

2015-01-01

Numerous studies have estimated a high intergenerational correlation in economic status. Such studies do not typically attend to potential biases that may arise due to survey attrition. Using the Panel Study of Income Dynamics – the data source most commonly used in prior studies – we demonstrate that attrition is particularly high for low-income adult children with low-income parents and particularly low for high-income adult children with high-income parents. Because of this pattern of attrition, intergenerational upward mobility has been overstated for low-income families and downward mobility has been understated for high-income families. The bias among low-income families is greater than the bias among high-income families implying that intergenerational elasticity in family income is higher than previous estimates with the Panel Study of Income Dynamics would suggest. PMID:26251655

Attrition in the kimberlite system

NASA Astrophysics Data System (ADS)

Jones, Thomas J.; Russell, James K.

2018-05-01

The sustained transportation of particles in a suspension commonly results in particle attrition leading to grain size reduction and shape modification. Particle attrition is a well-studied phenomenon that has mainly focussed on sediments produced in aeolian or fluvial environments. Here, we present analogue experiments designed to explore processes of attrition in the kimberlite system; we focus on olivine as it is the most abundant constituent of kimberlite. The attrition experiments on olivine use separate experimental set-ups to approximate two natural environments relevant to kimberlites. Tumbling mill experiments feature a low energy system supporting near continual particle-particle contact and are relevant to re-sedimentation and dispersal processes. Experiments performed in a fluidized particle bed constitute a substantially higher energy environment pertinent to kimberlite ascent and eruption. The run-products of each experiment are analysed for grain size reduction and shape modification and these data are used to elucidate the rates and extents of olivine attrition as a function of time and energy. Lastly, we model the two experimental datasets with an empirical rate equation that describes the production of daughter products (fines) with time. Both datasets approach a fines production limit, or plateau, at long particle residence times; the fluidized system is much more efficient producing a substantially higher fines content and reaches the plateau faster. Our experimental results and models provide a way to forensically examine a wide range of processes relevant to kimberlite on the basis of olivine size and shape properties.

High attrition among HIV-infected patients with advanced disease treated in an intermediary referral center in Maputo, Mozambique.

PubMed

Molfino, Lucas; Kumar, Ajay M V; Isaakidis, Petros; Van den Bergh, Rafael; Khogali, Mohamed; Hinderaker, Sven G; Magaia, Alice; Lobo, Sheila; Edwards, Celeste Gracia; Walter, Jan

2014-01-01

In Mozambique, antiretroviral therapy (ART) scale-up has been successfully implemented. However, attrition in care remains a major programmatic challenge. In 2009, an intermediary-level HIV referral center was created in Maputo to ensure access to specialized care for HIV-infected patients with complications (advanced clinical-immunological stage, Kaposi sarcoma, or suspected ART failure). To determine the attrition from care and to identify risk factors that lead to high attrition among patients referred to an intermediary-level HIV referral center. This was a retrospective cohort study from 2009 to 2011. A total of 1,657 patients were enrolled, 847 (51%) were men, the mean age was 36 years (standard deviation: 11), the mean CD4 count was 27 cells/µl (interquartile range: 11-44), and one-third were severely malnourished. The main reasons for referral were advanced clinical stages (WHO stages 3 and 4, and CD4 count <50 cells/µl) in 70% of the cases, and 19% had Kaposi sarcoma. The overall attrition rate was 28.7 per 100 person-years (PYs) - the mortality rate was 5.0 (95% confidence interval [CI]: 4.2-5.9) per 100 PYs, and the loss-to-follow-up rate was 23.7 (95% CI: 21.9-25.6) per 100 PYs. There were 793 attritions - 137 deaths and 656 lost to follow-up (LTFU); 77% of all attrition happened within the first year. The factors independently associated with attrition were male sex (adjusted hazard ratio [aHR]: 1.15, 95% CI: 1.0-1.3), low body mass index (aHR: 1.51, 95% CI: 1.2-1.8), WHO clinical stage 3 or 4 (aHR: 1.30, 95% CI: 1.0-1.6; and aHR: 1.91, 95% CI: 1.4-2.5), later year of enrollment (aHR 1.61, 95% CI 1.3-1.9), and 'being already on ART' at enrollment (aHR 13.71, 95% CI 11.4-16.4). Attrition rates among HIV-infected patients enrolled in an intermediary referral center were high, mainly related to advanced stage of clinical disease. Measures are required to address this, including innovative strategies for HIV-testing uptake, earlier ART initiation and nutritional supplementation, and special attention to men and those who are already on ART at enrolment. Qualitative research is required to understand the reasons for being LTFU and design informed evidence-based interventions.

Does reading in shallow L1 orthography slow attrition of language-specific morphological structures?

PubMed

Zaretsky, Elena; Bar-Shalom, Eva G

2010-01-01

This study looks at the relationship between L1 (Russian) attrition and L1 reading ability in Russian-English-speaking bilingual children. Ten Russian-English bilingual children and 10 adults participated in this study. Nine out of 10 children participants were born in the US and used L1 as their primary language of interaction within the family, but the intensity and the length of uninterrupted L1 exposure differed for each child. All participants were tested on perception (grammaticality judgement) and production (narrative) tasks to assess their sensitivity to and retention of the morphosyntactic structure of L1. All children showed some attrition of grammatical morphemes, specifically in the Russian systems of declension and conjugation; however, the degree of attrition correlated with reading ability in L1, i.e. children with L1 reading skills showed a lesser degree of attrition for some language-specific morphosyntactic structures. This finding shows interdependence of oral and reading skills and points to the role reading in language with shallow orthography may play in preservation of L1 grammatical structures in oral language. The implications for the clinical applications are also discussed.

Toward a clinically useful method of predicting early breast-feeding attrition.

PubMed

Lewallen, Lynne Porter; Dick, Margaret J; Wall, Yolanda; Zickefoose, Kimberly Taylor; Hannah, Susan Hensley; Flowers, Janet; Powell, Wanda

2006-08-01

The overall purpose of this study was to revise and test an instrument to identify, during the early postpartum period, women at risk for early breast-feeding attrition. This study was completed in two phases: the first phase tested a revision of the Breast-Feeding Attrition Prediction Tool (BAPT); the second, a new instrument, the Breast-Feeding Attitude Scale (BrAS), which was adapted from the BAPT. The two phases of this study involved 415 pregnant and postpartum women. Women answered questions either by phone (pregnant women) or in their hospital rooms after delivery (postpartum women). Data were analyzed using t tests and reliability analysis. The BAPT did not predict early breast-feeding attrition; however, the BrAS did differentiate between the attitudes of breast-feeding women and those of formula-feeding women and had adequate reliability. Women at risk for early breast-feeding attrition should be identified early so nursing interventions can be directed toward preventing early unintended weaning. Although the BrAS did not reliably identify women at risk in this sample, it did highlight important differences between breast-feeding and formula-feeding women that can be used in designing preconceptional or prenatal educational assessments and interventions.

Attrition of Tyee Formation Sandstone in a Natural Fluvial System

NASA Astrophysics Data System (ADS)

brandes, J. B.; Sanfilippo, J. D.; Lancaster, S. T.

2013-12-01

The data from this study will provide a rate of attrition with respect to change in volume, time and distance in a natural stream setting. Sandstone gravel attrition has been observed in previous studies with the use of rock tumblers, but measurements in natural systems are rare or absent. This study will use rocks with implanted passive integrated transponders (PIT) tags to track sediment movement. The study area is a natural mountain stream of approximately 4m width and 1m depth. This study is part of larger study of sediment transport. The rock volumes will be recorded prior to placement in an active channel using water displacement, the specific location along the channel will be recorded, and each tracer rock will be tracked using its individual radio frequency identification (RFID) number. Tracer rock deployment will occur before the annual high-water season. After one rainy season, the rocks will be located and removed from the stream using a radio frequency mobile radio frequency tracker. Their travel distances will be recorded and final volumes determined. Differences between initial and final volumes and travel distances will yield a distribution of attrition rates and, therefore, a mean gravel attrition rate.

Attrition in the RAND Health Insurance Experiment: a response to Nyman.

PubMed

Newhouse, Joseph P; Brook, Robert H; Duan, Naihua; Keeler, Emmett B; Leibowitz, Arleen; Manning, Willard G; Marquis, M Susan; Morris, Carl N; Phelps, Charles E; Rolph, John E

2008-04-01

In a prior article in this journal, John Nyman argues that the effect on health care use and spending found in the RAND Health Insurance Experiment is an artifact of greater voluntary attrition in the cost-sharing plans relative to the free care plan. Specifically, he speculates that those in the cost-sharing plans, when faced with a hospitalization, withdrew. His argument is implausible because (1) families facing a hospitalization would be worse off financially by withdrawing; (2) a large number of observational studies find a similar effect of cost sharing on use; (3) those who left did not differ in their utilization prior to leaving; (4) if there had been no attrition and cost sharing did not reduce hospitalization rates, each adult in each family that withdrew would have had to have been hospitalized once each year for the duration of time they would otherwise have been in the experiment, an implausibly high rate; (5) there are benign explanations for the higher attrition in the cost-sharing plans. Finally, we obtained follow-up health-status data on the great majority of those who left prematurely. We found the health-status findings were insensitive to the inclusion of the attrition cases.

Prevalence of dental attrition in in vitro fertilization children of West Bengal

PubMed Central

Kar, Sudipta; Sarkar, Subrata; Mukherjee, Ananya

2014-01-01

CONTEXT: Dental attrition is one of the problems affecting the tooth structure. It may affect both in vitro fertilization (IVF) and spontaneously conceived children. AIMS: This study was aimed to evaluate and to compare the prevalence of dental attrition in deciduous dentition of IVF and spontaneously conceived children. SETTINGS AND DESIGN: In a cross-sectional case control study dental attrition status of 3-5 years old children were assessed. The case group consisted of term, singleton babies who were the outcome of IVF in the studied area in 2009. SUBJECTS AND METHODS: The control group consisted of term, first child, singleton and spontaneously conceived 3-5 years old children who were also resident of the studied area. A sample of 153 IVF and 153 spontaneously conceived children was examined according to Hansson and Nilner classification. STATISTICAL ANALYSIS USED: Statistical analysis was carried out using Chi-square tests (χ2 ) or Z test. RESULTS: No statistically significant difference found in studied (IVF children) and control group (spontaneously conceived children). CONCLUSIONS: IVF children are considered same as spontaneously conceived children when studied in relation to dental attrition status. PMID:24829529

I Ain't Gonna Make It. Comparing Job Demands-Resources and Attrition Intention Between Senior Teachers and Senior Employees of Six Other Occupational Categories in Flanders.

PubMed

Van Droogenbroeck, Filip; Spruyt, Bram

2016-07-01

Teachers are often thought to retire early and have more stress and burnout than other human service professionals. In this article, we investigate attrition intention amongst senior teachers and senior employees of six other blue- and white-collar occupational categories using the Job Demands-Resources (JD-R) model. We followed a two-step approach. First, analysis of variance and logistic regression analysis was used to assess differences in the level of job demands, resources, and attrition intention between occupations for male and female employees separately. Subsequently, multiple group path analysis was used to assess the invariance of the JD-R model across occupational groups and genders. We used representative data gathered in Flanders among 6,810 senior employees (45 years or older). Results indicate that there are differences in the determinants of attrition intention between men and women. The differences in attrition intention are minimal between occupations once controlled for job demands and resources. In addition, the JD-R model is largely invariant across white-collar occupations and gender. We provide support for both the energetic and motivational process of the JD-R model. © The Author(s) 2016.

Demographic and Psychological Predictors of Panel Attrition: Evidence from the New Zealand Attitudes and Values Study

PubMed Central

Satherley, Nicole; Milojev, Petar; Greaves, Lara M.; Huang, Yanshu; Osborne, Danny; Bulbulia, Joseph; Sibley, Chris G.

2015-01-01

This study examines attrition rates over the first four years of the New Zealand Attitudes and Values Study, a longitudinal national panel sample of New Zealand adults. We report the base rate and covariates for the following four distinct classes of respondents: explicit withdrawals, lost respondents, intermittent respondents and constant respondents. A multinomial logistic regression examined an extensive range of demographic and socio-psychological covariates (among them the Big-Six personality traits) associated with membership in these classes (N = 5,814). Results indicated that men, Māori and Asian peoples were less likely to be constant respondents. Conscientiousness and Honesty-Humility were also positively associated with membership in the constant respondent class. Notably, the effect sizes for the socio-psychological covariates of panel attrition tended to match or exceed those of standard demographic covariates. This investigation broadens the focus of research on panel attrition beyond demographics by including a comprehensive set of socio-psychological covariates. Our findings show that core psychological covariates convey important information about panel attrition, and are practically important to the management of longitudinal panel samples like the New Zealand Attitudes and Values Study. PMID:25793746

Models of Conflict, with Explicit Representation of Command and Control Capabilities and Vulnerabilities.

DTIC Science & Technology

1981-02-01

converting Bu’s to Bal s Case 2: Pa,cc (t) = 0.25 + 0.075t = PaA(t) =1.0 In this case a space (and hence time) varying representation of the attrition rate...34 a Attrition rates can be made time ( space ) dependent. * Note that the attrition law is assumed for illustration only to be in accordance with a...34 Systems Reserach Lab., Dept. of Industrial Eng., University of Michigan. Gaver, D.P. and Tonguc K. (1979) "Modelling the influnece of information on

SRB attrition rate study of the aft skirt due to water impact cavity collapse loading

NASA Technical Reports Server (NTRS)

Crockett, C. D.

1976-01-01

A methodology was presented so that realistic attrition prediction could aid in selecting an optimum design option for minimizing the effects of updated loads on the Space Shuttle Solid Rocket Booster (SRB) aft skirt. The updated loads resulted in water impact attrition rates greater than 10 percent for the aft skirt structure. Adding weight to reinforce the aft skirt was undesirable. The refined method treats the occurrences of the load distribution probabilistically, radially and longitudinally, with respect to the critical structural response.

A Self-Regulation-Based eHealth Intervention to Promote a Healthy Lifestyle: Investigating User and Website Characteristics Related to Attrition.

PubMed

Van der Mispel, Celien; Poppe, Louise; Crombez, Geert; Verloigne, Maïté; De Bourdeaudhuij, Ilse

2017-07-11

eHealth interventions can reach large populations and are effective in increasing physical activity (PA) and fruit and vegetable intake. Nevertheless, the effects of eHealth interventions are overshadowed by high attrition rates. Examining more closely when users decide to leave the intervention can help eHealth developers to make informed decisions about which intervention components should be reshaped or simply removed. Investigating which users are more likely to quit an intervention can inform developers about whether and how their intervention should be adapted to specific subgroups of users. This study investigated the pattern of attrition in a Web-based intervention to increase PA, fruit, and vegetable intake. The first aim was to describe attrition rates according to different self-regulation components. A second aim was to investigate whether certain user characteristics are predictors for start session completion, returning to a follow-up session and intervention completion. The sample consisted of 549 adults who participated in an online intervention, based on self-regulation theory, to promote PA and fruit and vegetable intake, called "MyPlan 1.0." Using descriptive analysis, attrition was explored per self-regulation component (eg, action planning and coping planning). To identify which user characteristics predict completion, logistic regression analyses were conducted. At the end of the intervention program, there was an attrition rate of 78.2% (330/422). Attrition rates were very similar for the different self-regulation components. However, attrition levels were higher for the fulfillment of questionnaires (eg, to generate tailored feedback) than for the more interactive components. The highest amount of attrition could be observed when people were asked to make their own action plan. There were no significant predictors for first session completion. Yet, two subgroups had a lower chance to complete the intervention, namely male users (OR: 2.24, 95% CI=1.23-4.08) and younger adults (OR: 1.02, 95% CI=1.00-1.04). Furthermore, younger adults were less likely to return to the website for the first follow-up after one week (OR: 1.03, 95% CI=1.01-1.04). This study informs us that eHealth interventions should avoid the use of extensive questionnaires and that users should be provided with a rationale for several components (eg, making an action plan and completing questions). Furthermore, future interventions should focus first on motivating users for the behavior change before guiding them through action planning. Though, this study provides no evidence for removal of one of the self-regulation techniques based on attrition rates. Finally, strong efforts are needed to motivate male users and younger adults to complete eHealth interventions. ©Celien Van der Mispel, Louise Poppe, Geert Crombez, Maïté Verloigne, Ilse De Bourdeaudhuij. Originally published in the Journal of Medical Internet Research (http://www.jmir.org), 11.07.2017.

Forest dynamics in the U.S. indicate disproportionate attrition in western forests, rural areas and public lands

PubMed Central

2017-01-01

Forests are experiencing significant changes; studying geographic patterns in forests is critical in understanding the impact of forest dynamics to biodiversity, soil erosion, water chemistry and climate. Few studies have examined forest geographic pattern changes other than fragmentation; however, other spatial processes of forest dynamics are of equal importance. Here, we study forest attrition, the complete removal of forest patches, that can result in complete habitat loss, severe decline of population sizes and species richness, and shifts of local and regional environmental conditions. We aim to develop a simple yet insightful proximity-based spatial indicator capturing forest attrition that is independent of spatial scale and boundaries with worldwide application potential. Using this proximity indicator, we evaluate forest attrition across ecoregions, land ownership and urbanization stratifications across continental United States of America. Nationally, the total forest cover loss was approximately 90,400 km2, roughly the size of the state of Maine, constituting a decline of 2.96%. Examining the spatial arrangement of this change the average FAD was 3674m in 1992 and increased by 514m or 14.0% in 2001. Simulations of forest cover loss indicate only a 10m FAD increase suggesting that the observed FAD increase was more than an order of magnitude higher than expected. Furthermore, forest attrition is considerably higher in the western United States, in rural areas and in public lands. Our mathematical model (R2 = 0.93) supports estimation of attrition for a given forest cover. The FAD metric quantifies forest attrition across spatial scales and geographic boundaries and assesses unambiguously changes over time. The metric is applicable to any landscape and offers a new complementary insight on forest landscape patterns from local to global scales, improving future exploration of drivers and repercussions of forest cover changes and supporting more informative management of forest carbon, changing climate and species biodiversity. PMID:28225787

Attrition during a randomized controlled trial of reduced nicotine content cigarettes as a proxy for understanding acceptability of nicotine product standards

PubMed Central

Mercincavage, Melissa; Wileyto, E. Paul; Saddleson, Megan L.; Lochbuehler, Kirsten; Donny, Eric C.; Strasser, Andrew A.

2017-01-01

Aims To determine (1) if nicotine content affects study attrition – a potential behavioral measure of acceptability – in a trial that required compliance with three levels of reduced nicotine content (RNC) cigarettes, and (2) if attrition is associated with subjective and behavioral responses to RNC cigarettes. Design Secondary analysis of a 35-day, parallel design, open-label, randomized controlled trial. After a 5-day baseline period, participants were randomized to smoke for three, 10-day periods: their preferred brand (control group), or RNC cigarettes with three nicotine levels in a within-subject, stepdown (1 group: high-moderate-low) or non-stepdown (5 groups: high-low-moderate, low-moderate-high, low-high-moderate, moderate-low-high, moderate-high-low) fashion. Setting A single site in Philadelphia, Pennsylvania, USA. Participants 246 non-treatment-seeking daily smokers (M age = 39.52, CPD = 20.95, 68.3% White) were recruited from October 2007 to June 2013. Measurements The primary outcome was attrition. Key predictors were nicotine content transition and study period. Exploratory predictors were taste and strength subjective ratings, total puff volume, and carbon monoxide (CO) boost. Covariates included: age, gender, race, education, and nicotine dependence. Findings Overall attrition was 31.3% (n = 77): 24.1% of the control and 25.0% of the stepdown RNC cigarette groups dropped out vs. 44.6% of non-stepdown groups (p = 0.006). Compared with controls, attrition odds were 4.5 and 4.7 times greater among smokers transitioning from preferred and the highest RNC cigarettes to the lowest RNC cigarettes, respectively (p’s = .001 and .003). Providing more favorable initial taste ratings of study cigarettes decreased attrition odds by 2% (p = .012). Conclusions The majority of participants completed a 35-day trial of varying levels of reduced nicotine content cigarettes. Participant drop-out was greater for cigarettes with lower nicotine content and less in smokers reporting more favorable subjective ratings of the cigarettes. PMID:28107596

Factors associated with study attrition in a pilot randomised controlled trial to explore the role of exercise-assisted reduction to stop (EARS) smoking in disadvantaged groups.

PubMed

Thompson, T P; Greaves, C J; Ayres, R; Aveyard, P; Warren, F C; Byng, R; Taylor, R S; Campbell, J L; Ussher, M; Michie, S; West, R; Taylor, A H

2016-10-27

Study attrition has the potential to compromise a trial's internal and external validity. The aim of the present study was to identify factors associated with participant attrition in a pilot trial of the effectiveness of a novel behavioural support intervention focused on increasing physical activity to reduce smoking, to inform the methods to reduce attrition in a definitive trial. Disadvantaged smokers who wanted to reduce but not quit were randomised (N = 99), of whom 61 (62 %) completed follow-up assessments at 16 weeks. Univariable logistic regression was conducted to determine the effects of intervention arm, method of recruitment, and participant characteristics (sociodemographic factors, and lifestyle, behavioural and attitudinal characteristics) on attrition, followed by multivariable logistic regression on those factors found to be related to attrition. Participants with low confidence to quit, and who were undertaking less than 150 mins of moderate and vigorous physical activity per week at baseline were less likely to complete the 16-week follow-up assessment. Exploratory analysis revealed that those who were lost to follow-up early in the trial (i.e., by 4 weeks), compared with those completing the study, were younger, had smoked for fewer years and had lower confidence to quit in the next 6 months. Participants who recorded a higher expired air carbon monoxide reading at baseline were more likely to drop out late in the study, as were those recruited via follow-up telephone calls. Multivariable analyses showed that only completing less than 150 mins of physical activity retained any confidence in predicting attrition in the presence of other variables. The findings indicate that those who take more effort to be recruited, are younger, are heavier smokers, have less confidence to quit, and are less physically active are more likely to withdraw or be lost to follow-up.

Where do all the undergraduate and new graduate nurses go and why? A search for empirical research evidence.

PubMed

Gaynor, Lynda; Gallasch, Tamara; Yorkston, Emily; Stewart, Simon; Turner, Catherine

To review the published scientific literature for studies quantifying or examining factors associated with the attrition of undergraduate nursing students in pre-registration programs and the retention of graduate nurses in the workforce. The following selection criteria were used to systematically search the literature: target populations were either students in pre-registration nursing programs or registered nurses in their graduate year; the studies were to be primary observational or analytical (cross-sectional, case-control or prospective cohort studies) in design; and outcome measures were attrition in undergraduate programs and/or retention of graduates within the workforce. Three authors guided by a standardised procedure performed data extraction and quality assessment independently. Synthesis of the data appears in text and tabular format. Due to the heterogenic nature of the study methods, meta-analysis was not possible. This review found only four studies that met all inclusion criteria. All four studies examined undergraduate attrition as an outcome with two studies reporting a range of 25-27% attrition within the first year. No studies were found that quantified or examined retention of new graduates as an outcome measure. Only two of the four studies followed cohorts of students prospectively and were able to provide a high level of evidence, although each of these studies was designed to assess specific exposures as potential predictors of attrition, rather than assess actual factors associated with students leaving their program. There is a paucity of research studies in the literature from which evidence quantifying attrition and retention and the reasons why students leave undergraduate nursing programs or new graduates leave the profession can be obtained. Clearly there is a need to systematically track undergraduates and new graduates to quantify and understand attrition, retention and workforce choices within the nursing profession and begin to build this evidence-base.

Association between self-reported bruxism activity and occurrence of dental attrition, abfraction, and occlusal pits on natural teeth.

PubMed

Tsiggos, Nikolaos; Tortopidis, Dimitrios; Hatzikyriakos, Andreas; Menexes, George

2008-07-01

It is unclear whether subjects who report tooth clenching and/or grinding have more noticeable clinical signs of dental attrition, abfractions, and occlusal pits on their natural teeth than subjects who do not report bruxism activity. The purpose of this study was to determine whether there was an association between self-reported (or not reported) bruxism activity and occurrence of dental attrition (anterior, posterior), abfractions, and occlusal pits on natural teeth. One hundred and two volunteer adult Greek subjects (mean age 44.6 +/-5.7 years) were classified into 2 groups (50 self-reported bruxers and 52 nonbruxers) according to 2 inquires regarding grinding and/or clenching of their teeth. Dental attrition (anterior, posterior) was assessed by 2 calibrated experienced examiners on diagnostic casts on a tooth-by-tooth basis, using a previously well established ordinal scale. Abfraction lesions (V-shaped, in the cervical region) and occlusal pits were recorded if these clinical signs were found on at least 2 natural teeth. Statistical comparisons between the 2 groups relative to the distribution of the occurrence of the 4 clinical signs were performed by means of the exact version of the chi-square test. The Fisher's exact test was used for the comparison of percentages. The intra- and interexaminer reliability was assessed by means of the Cohen's kappa coefficient (alpha=.05). The results demonstrated that there was a significant association between self-reported bruxism and occurrence of the 4 clinical signs. Although the 2 groups were significantly different according to the distribution of the 4 clinical signs, the greatest differences occurred for the anterior and posterior attrition signs. In this study, the occurrence of 4 clinical signs (posterior or anterior dental attrition, abfractions, and occlusal pits) was associated with self-reported bruxers. It is suggested that, primarily, signs of dental attrition may differentiate self-reported bruxers from nonbruxer subjects.

The Impact of Motor Axon Misdirection and Attrition on Behavioral Deficit Following Experimental Nerve Injuries

PubMed Central

Alant, Jacob Daniel de Villiers; Senjaya, Ferry; Ivanovic, Aleksandra; Forden, Joanne; Shakhbazau, Antos; Midha, Rajiv

2013-01-01

Peripheral nerve transection and neuroma-in-continuity injuries are associated with permanent functional deficits, often despite successful end-organ reinnervation. Axonal misdirection with non-specific reinnervation, frustrated regeneration and axonal attrition are believed to be among the anatomical substrates that underlie the poor functional recovery associated with these devastating injuries. Yet, functional deficits associated with axonal misdirection in experimental neuroma-in-continuity injuries have not yet been studied. We hypothesized that experimental neuroma-in-continuity injuries would result in motor axon misdirection and attrition with proportional persistent functional deficits. The femoral nerve misdirection model was exploited to assess major motor pathway misdirection and axonal attrition over a spectrum of experimental nerve injuries, with neuroma-in-continuity injuries simulated by the combination of compression and traction forces in 42 male rats. Sciatic nerve injuries were employed in an additional 42 rats, to evaluate the contribution of axonal misdirection to locomotor deficits by a ladder rung task up to 12 weeks. Retrograde motor neuron labeling techniques were utilized to determine the degree of axonal misdirection and attrition. Characteristic histological neuroma-in-continuity features were demonstrated in the neuroma-in-continuity groups and poor functional recovery was seen despite successful nerve regeneration and muscle reinnervation. Good positive and negative correlations were observed respectively between axonal misdirection (p<.0001, r2=.67), motor neuron counts (attrition) (p<.0001, r2=.69) and final functional deficits. We demonstrate prominent motor axon misdirection and attrition in neuroma-in-continuity and transection injuries of mixed motor nerves that contribute to the long-term functional deficits. Although widely accepted in theory, to our knowledge, this is the first experimental evidence to convincingly demonstrate these correlations with data inclusive of the neuroma-in-continuity spectrum. This work emphasizes the need to focus on strategies that promote both robust and accurate nerve regeneration to optimize functional recovery. It also demonstrates that clinically relevant neuroma-in-continuity injuries can now also be subjected to experimental investigation. PMID:24282624

Forest dynamics in the U.S. indicate disproportionate attrition in western forests, rural areas and public lands.

PubMed

Yang, Sheng; Mountrakis, Giorgos

2017-01-01

Forests are experiencing significant changes; studying geographic patterns in forests is critical in understanding the impact of forest dynamics to biodiversity, soil erosion, water chemistry and climate. Few studies have examined forest geographic pattern changes other than fragmentation; however, other spatial processes of forest dynamics are of equal importance. Here, we study forest attrition, the complete removal of forest patches, that can result in complete habitat loss, severe decline of population sizes and species richness, and shifts of local and regional environmental conditions. We aim to develop a simple yet insightful proximity-based spatial indicator capturing forest attrition that is independent of spatial scale and boundaries with worldwide application potential. Using this proximity indicator, we evaluate forest attrition across ecoregions, land ownership and urbanization stratifications across continental United States of America. Nationally, the total forest cover loss was approximately 90,400 km2, roughly the size of the state of Maine, constituting a decline of 2.96%. Examining the spatial arrangement of this change the average FAD was 3674m in 1992 and increased by 514m or 14.0% in 2001. Simulations of forest cover loss indicate only a 10m FAD increase suggesting that the observed FAD increase was more than an order of magnitude higher than expected. Furthermore, forest attrition is considerably higher in the western United States, in rural areas and in public lands. Our mathematical model (R2 = 0.93) supports estimation of attrition for a given forest cover. The FAD metric quantifies forest attrition across spatial scales and geographic boundaries and assesses unambiguously changes over time. The metric is applicable to any landscape and offers a new complementary insight on forest landscape patterns from local to global scales, improving future exploration of drivers and repercussions of forest cover changes and supporting more informative management of forest carbon, changing climate and species biodiversity.

[Diagnosis and therapy of particle disease in total hip arthroplasty].

PubMed

Müller, M; Wassilew, G; Perka, C

2015-04-01

Particle disease is caused by periarticular accumulation of attrition particles and the inflammatory reaction of the body's tissue. This process may result in osteolysis or soft tissue transformation which presents itself symptomless in the beginning and can proceed to aseptic implant loosening, fracture, implant breaking as a result of the inappropriate osseous support and to algetic and destructive soft tissue reactions as well. Attrition particles originate from tribological pairing, and the extent of the attrition or the particle concentration depend on different factors as there are the tribological pairing's material, the head size, the patient's level of activity, and the implant position. Attrition particles can also be found in the range of any modular connection. Particle disease and its resulting morphological alterations of the tribological pairing is one of the most frequent reasons for re-operation in hip endoprosthetics. Georg Thieme Verlag KG Stuttgart · New York.

Confirming the Lanchestrian linear-logarithmic model of attrition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hartley, D.S. III.

1990-12-01

This paper is the fourth in a series of reports on the breakthrough research in historical validation of attrition in conflict. Significant defense policy decisions, including weapons acquisition and arms reduction, are based in part on models of conflict. Most of these models are driven by their attrition algorithms, usually forms of the Lanchester square and linear laws. None of these algorithms have been validated. The results of this paper confirm the results of earlier papers, using a large database of historical results. The homogeneous linear-logarithmic Lanchestrian attrition model is validated to the extent possible with current initial and finalmore » force size data and is consistent with the Iwo Jima data. A particular differential linear-logarithmic model is described that fits the data very well. A version of Helmbold's victory predicting parameter is also confirmed, with an associated probability function. 37 refs., 73 figs., 68 tabs.« less

Factors associated with attrition rate in a supportive care service for substance using pregnant women in Brazil.

PubMed

Avilla, Rosa Marina; Surjan, Juliana; de Fátima Ratto Padin, Maria; Canfield, Martha; Laranjeira, Ronaldo Ramos; Mitsuhiro, SandroSendin

2017-10-01

Retaining substance using women in antenatal care remains a major challenge. This study explored factors associated with attrition rate among women with substance use problems attending a supportive care service during pregnancy and soon after the birth of the infant. Records of 166 women's antenatal consultations were analyzed. Attrition rate was high (75/166, 45.2%), and was associated with women having no schooling/primary schooling only, no family contact, having child(ren), crack-cocaine use, poly drug use, and substance use problems by the expected child's father. Attrition may be the outcome of socio-demographic, family, individual, and substance use issues not fully addressed in prenatal interventions. Identification of who are at risk for dropping out affords services with an opportunity to prevent its occurrence. (Am J Addict 2017;26:676-679). © 2017 American Academy of Addiction Psychiatry.

Screening of zinc-based sorbents for hot-gas desulfurization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joong B. Lee; Chong K. Ryu; Chang K. Yi

2008-03-15

Highly reactive and attrition-resistant ZnO-based sorbents that are suitable for bubbling fluidized-bed reactors can be produced using the spray-drying method. Most of the ZnO-based sorbents prepared here (ZAC-X, X = 18N-25N) satisfy the physical and chemical criteria for bubbling fluidized-bed application (spherical shape, average particle size, 90-110 {mu}m; size distribution, 40-230 {mu}m; bulk density, 0.9-1.0 g/mL; attrition index (AI), 40-80%; sulfur sorption capacity, 14-17 wt %; sorbent use, 70-80%). The performance test of the ZAC-C sorbent at Korea Institute of Energy Research (KIER) with a bubbling fluidized-bed for 70 h also demonstrated that it had good sulfidation and regeneration performancemore » (11 wt % sorption capacity and 52% sorbent use) as well as reasonable attrition resistance (1.1% attrition loss for 70 h). 14 refs., 7 figs., 6 tabs.« less

Comparison of attrition test methods: ASTM standard fluidized bed vs jet cup

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, R.; Goodwin, J.G. Jr.; Jothimurugesan, K.

2000-05-01

Attrition resistance is one of the key design parameters for catalysts used in fluidized-bed and slurry phase types of reactors. The ASTM fluidized-bed test has been one of the most commonly used attrition resistance evaluation methods; however, it requires the use of 50 g samples--a large amount for catalyst development studies. Recently a test using the jet cup requiring only 5 g samples has been proposed. In the present study, two series of spray-dried iron catalysts were evaluated using both the ASTM fluidized-bed test and a test based on the jet cup to determine this comparability. It is shown thatmore » the two tests give comparable results. This paper, by reporting a comparison of the jet-cup test with the ASTM standard, provides a basis for utilizing the more efficient jet cup with confidence in catalyst attrition studies.« less

Reasons for African American student attrition from school psychology programs.

PubMed

Proctor, Sherrie L; Truscott, Stephen D

2012-10-01

This phenomenological study used a series of three in-depth interviews with seven African American participants, for a total of 21 interviews, to explore their experiences in the specialist and doctoral level school psychology programs they left prior to obtaining a professional entry-level degree. The study's purpose was to investigate what factors contributed to participants' attrition. Findings indicate that misalignment between participants' career aims and the practice of school psychology (as presented in the programs they left) contributed to attrition. Poor relationships with school psychology faculty and program cohort peers also played a role in participants' decisions to leave school psychology programs. Results offer a unique lens into racial issues in school psychology. Recommendations for faculty and others interested in preventing African Americans' attrition from school psychology graduate education are discussed. Copyright © 2012 Society for the Study of School Psychology. Published by Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Wei; DeCroix, David; Sun, Xin

The attrition of particles is a major industrial concern in many fluidization systems as it can have undesired effects on the product quality and on the reliable operation of process equipment. Therefore, to accomodate the screening and selection of catalysts for a specific process in fluidized beds, risers, or cyclone applications, their attrition propensity is usually estimated through jet cup attrition testing, where the test material is subjected to high gas velocities in a jet cup. However, this method is far from perfect despite its popularity, largely due to its inconsistency in different testing set-ups. In order to better understandmore » the jet cup testing results as well as their sensitivity to different operating conditions, a coupled computational fluid dynamic (CFD) - discrete element method (DEM) model has been developed in the current study to investigate the particle attrition in a jet cup and its dependence on various factors, e.g. jet velocity, initial particle size, particle density, and apparatus geometry.« less

Migration Selection, Protection, and Acculturation in Health: A Binational Perspective on Older Adults

PubMed Central

Riosmena, Fernando; Wong, Rebeca; Palloni, Alberto

2012-01-01

In this article, we test for four potential explanations of the Hispanic Health Paradox (HHP): the “salmon bias,” emigration selection, and sociocultural protection originating in either destination or sending country. To reduce biases related to attrition by return migration typical of most U.S.-based surveys, we combine data from the Mexican Health and Aging Study in Mexico and the U.S. National Health Interview Survey to compare self-reported diabetes, hypertension, current smoking, obesity, and self-rated health among Mexican-born men ages 50 and older according to their previous U.S. migration experience, and U.S.-born Mexican Americans and non-Hispanic whites. We also use height, a measure of health during childhood, to bolster some of our tests. We find an immigrant advantage relative to non-Hispanic whites in hypertension and, to a lesser extent, obesity. We find evidence consistent with emigration selection and the salmon bias in height, hypertension, and self-rated health among immigrants with less than 15 years of experience in the United States; we do not find conclusive evidence consistent with sociocultural protection mechanisms. Finally, we illustrate that although ignoring return migrants when testing for the HHP and its mechanisms, as well as for the association between U.S. experience and health, exaggerates these associations, they are not fully driven by return migration-related attrition. PMID:23192395

Biocompatibility of nanoactuators: stem cell growth on laser-generated nickel-titanium shape memory alloy nanoparticles

NASA Astrophysics Data System (ADS)

Barcikowski, Stephan; Hahn, Anne; Guggenheim, Merlin; Reimers, Kerstin; Ostendorf, Andreas

2010-06-01

Nanoactuators made from nanoparticulate NiTi shape memory alloy show potential in the mechanical stimulation of bone tissue formation from stem cells. We demonstrate the fabrication of Ni, Ti, and NiTi shape memory alloy nanoparticles and their biocompatibility to human adipose-derived stem cells. The stoichiometry and phase transformation property of the bulk alloy is preserved during attrition by femtosecond laser ablation in liquid, giving access to colloidal nanoactuators. No adverse effect on cell growth and attachment is observed in proliferation assay and environmental electron scanning microscopy, making this material attractive for mechanical stimulation of stem cells.

Attrition across the HIV cascade of care among a diverse cohort of women living with HIV in Canada.

PubMed

Kerkerian, Genevieve; Kestler, Mary; Carter, Allison; Wang, Lu; Kronfli, Nadine; Sereda, Paul; Roth, Eric; Milloy, M-J; Pick, Neora; Money, Deborah; Webster, Kath; Hogg, Robert S; de Pokomandy, Alexandra; Loutfy, Mona; Kaida, Angela

2018-06-15

In North America, women have lower engagement across the HIV cascade of care compared with men. Among women living with HIV (WLWH) in Canada, we measured the prevalence and correlates of attrition across cascade stages overall, and by key sub-populations. We analyzed baseline survey data regarding six nested stages of the HIV cascade among 1,424 WLWH enrolled in the Canadian HIV Sexual and Reproductive Health Cohort Study (CHIWOS), including: linked to care, retained in care, initiated antiretroviral therapy (ART), current ART use, ART adherence (≥90%), and viral suppression (<50 copies/mL). Logistic regression identified factors associated with attrition at each stage. Overall, 98% of WLWH were linked to care; 96% retained; 88% initiated ART; 83% were currently on ART; and, among those on ART, 68% were adherent and 72% were virally suppressed, with substantial variability by sub-population (49%-84%). The largest attrition occurred between current ART use and adherence (-17%), with the greatest losses among Indigenous women (-25%), women who use illicit drugs (-32%), and women incarcerated in the past year (-45%). Substantial attrition also occurred between linkage to care and ART initiation (-11%), with the greatest losses among women 16-29 years (-20%) and with unstable housing (-27%). Factors independently associated with attrition at viral suppression included household annual income, racial discrimination, incarceration history, age, and resilience. Overall, 28% of WLWH were lost across the HIV care cascade, with significant differences by stage, sub-population, and social inequities. Targeted interventions are needed to improve women's retention across the cascade.

Predictors of attrition with buprenorphine/naloxone treatment in opioid dependent youth.

PubMed

Warden, Diane; Subramaniam, Geetha A; Carmody, Thomas; Woody, George E; Minhajuddin, Abu; Poole, Sabrina A; Potter, Jennifer; Fishman, Marc; Bogenschutz, Michael; Patkar, Ashwin; Trivedi, Madhukar H

2012-09-01

In opioid dependent youth there is substantial attrition from medication-assisted treatment. If youth at risk for attrition can be identified at treatment entry or early in treatment, they can be targeted for interventions to help retain them in treatment. Opioid dependent adolescents and young adults (n=152), aged 15-21, were randomized to 12 weeks (BUP, n=74) or 2 weeks of detoxification (DETOX, n=78) with buprenorphine/naloxone (Bup/Nal), both in combination with 12 weeks of psychosocial treatment. Baseline and early treatment related predictors of treatment attrition were identified in each group using bivariate and multivariate logistic regression. In the DETOX group 36% left between weeks 2 and 4, at the end of the dose taper, while in the BUP group only 8% left by week 4. In the BUP group, early adherence to Bup/Nal, early opioid negative urines, use of any medications in the month prior to treatment entry, and lifetime non-heroin opioid use were associated with retention while prior 30-day hallucinogen use was associated with attrition. In the DETOX group, only use of sleep medications was associated with retention although not an independent predictor. A broad range of other pre-treatment characteristics was unrelated to attrition. Prompt attention to those with early non-adherence to medication or an early opioid positive urine, markers available in the first 2 weeks of treatment, may improve treatment retention. Extended Bup/Nal treatment appeared effective in improving treatment retention for youth with opioid dependence across a wide range of demographics, and pre-treatment clinical characteristics. Copyright © 2012 Elsevier Ltd. All rights reserved.

Predictors of attrition with buprenorphine/naloxone treatment in opioid dependent youth☆

PubMed Central

Warden, Diane; Subramaniam, Geetha A.; Carmody, Thomas; Woody, George E.; Minhajuddin, Abu; Poole, Sabrina A.; Potter, Jennifer; Fishman, Marc; Bogenschutz, Michael; Patkar, Ashwin; Trivedi, Madhukar H.

2012-01-01

Background In opioid dependent youth there is substantial attrition from medication-assisted treatment. If youth at risk for attrition can be identified at treatment entry or early in treatment, they can be targeted for interventions to help retain them in treatment. Methods Opioid dependent adolescents and young adults (n=152), aged 15–21, were randomized to 12 weeks (BUP, n=74) or 2 weeks of detoxification (DETOX, n=78) with buprenorphine/naloxone (Bup/Nal), both in combination with 12 weeks of psychosocial treatment. Baseline and early treatment related predictors of treatment attrition were identified in each group using bivariate and multivariate logistic regression. Results In the DETOX group 36% left between weeks 2 and 4, at the end of the dose taper, while in the BUP group only 8% left by week 4. In the BUP group, early adherence to Bup/Nal, early opioid negative urines, use of any medications in the month prior to treatment entry, and lifetime non-heroin opioid use were associated with retention while prior 30-day hallucinogen use was associated with attrition. In the DETOX group, only use of sleep medications was associated with retention although not an independent predictor. A broad range of other pre-treatment characteristics was unrelated to attrition. Conclusions Prompt attention to those with early non-adherence to medication or an early opioid positive urine, markers available in the first 2 weeks of treatment, may improve treatment retention. Extended Bup/ Nal treatment appeared effective in improving treatment retention for youth with opioid dependence across a wide range of demographics, and pre-treatment clinical characteristics. PMID:22626890

Attrition after Acceptance onto a Publicly Funded Bariatric Surgery Program.

PubMed

Taylor, Tamasin; Wang, Yijiao; Rogerson, William; Bavin, Lynda; Sharon, Cindy; Beban, Grant; Evennett, Nicholas; Gamble, Greg; Cundy, Timothy

2018-03-10

Factors such as ethnicity, gender, and socioeconomic status may play a role in both access to and attrition from bariatric programs before surgery is undertaken. New Zealand (NZ) has high rates of obesity in its Pacific population and the indigenous Māori. These groups also experience poorer health outcomes and therefore have the greatest need for surgery. A retrospective cross-sectional study of 704 people referred for and accepted onto a publicly funded bariatric surgery from 2007 to 2016. The demographic and clinical features of two groups were compared: those that completed surgery successfully (n = 326) and those that dropped out of the program before surgery (n = 378). We also attempted to identify factors associated with attrition. The attrition rate was high (54%), with a significant difference according to gender (men 66% vs 45% women, p < 0.001) and ethnicity (39% in NZ Europeans, 50% in Māori, and 73% in Pacific patients, p < 0.001). Two out of three European women proceeded to surgery, but fewer than one in seven Pacific men. Attrition was associated with having a higher mean BMI and being a smoker. Logistic regression modeling showed that while employment seemed to be protective against attrition for NZ Europeans (p < 0.004), it was not for Pacific patients. While there was no obvious bias in rates of referral, there is clearly a need for better ways to support Māori and Pacific people, and men in particular, to complete bariatric surgery. Further research is needed to clarify the socio-economic and cultural barriers that underlie this phenomenon.

[Attrition and poor performance in general practice training: age, competence and knowledge play a role].

PubMed

Vermeulen, Margit I; Kuyvenhoven, Marijke M; Zuithoff, N P A Peter; van der Graaf, Yolanda; Pieters, H M Ron

2011-01-01

To investigate which determinants are related to poor performance and forced attrition in the first year residency in general practice (GP). Observational retrospective cohort study. We collected data relating to personal characteristics such as age, sex and clinical experience from residents who started the GP training in Utrecht, the Netherlands, in the period March 2005-August 2007. We also collected competence scores from the domains 'medical expertise', 'doctor-patient communication' and 'professionalism', as well as scores on a national GP knowledge test. The outcome measures were 'poor performance' and 'forced attrition'. Multivariate logistic regression was used to analyse correlations between personal characteristics, competence scores on the 3 domains and knowledge scores in the first trimester on the one hand and poor performance or forced attrition on the other. 215 residents started the GP training. In the first trimester a quarter of the residents had an insufficient score in 1 or more of the domains. Competence scores were mutually correlated, but did not correlate with the knowledge score. 18 residents showed poor performance and 3 were forced to stop their training. Poor performance and forced attrition were correlated with age (adjusted odds ratio (OR): 1.1; 95% CI: 1.0-1.3), insufficient knowledge (adjusted OR: 8.9; 3.0-26.3) and medical expertise (adjusted OR: 2.1; 1.1-4.0) at the beginning of the training. Age, insufficient knowledge of general practice, and insufficient competence in the domain of 'medical expertise' at the beginning of the training are risk factors for poor performance by residents and attrition from their GP training.

The Environmental Factors Influencing Attrition.

ERIC Educational Resources Information Center

Villella, Edward F.

1986-01-01

Offers an economics/business-management perspective on student attrition, focusing on the external macro-environment (including such factors as government funding of education, changing enrollment patterns, and the increased number of postsecondary institutions) and the internal micro-environment (exhibiting characteristics of intangibility,…

Factors Affecting the Attrition Strength of Alumina Products

NASA Astrophysics Data System (ADS)

Sang, J. V.

The attrition strength of alumina is a matter of increasing interest. The aim of the present paper is to show how the strength of alumina is related to the precipitation parameters and to the morphology of the precursor hydrate particles.

Alternative Methods for Handling Attrition

PubMed Central

Foster, E. Michael; Fang, Grace Y.

2009-01-01

Using data from the evaluation of the Fast Track intervention, this article illustrates three methods for handling attrition. Multiple imputation and ignorable maximum likelihood estimation produce estimates that are similar to those based on listwise-deleted data. A panel selection model that allows for selective dropout reveals that highly aggressive boys accumulate in the treatment group over time and produces a larger estimate of treatment effect. In contrast, this model produces a smaller treatment effect for girls. The article's conclusion discusses the strengths and weaknesses of the alternative approaches and outlines ways in which researchers might improve their handling of attrition. PMID:15358906

Military Women in the Department of Defense, Volume 5

DTIC Science & Technology

1987-07-01

and reenlistments. promotion opportunity, frequency of overseas THREE YEAR ATTRITION BY SEX & EDUCATION FY 1983 COHORT DoD ACTIVE DUTYPERCEN7I...1001) . ALL, OTI IER CAUSES ’". FAILURE TO NIEET CRITI (A E][ 61 $rv ACTIVE DUTY THREE YEAR ATTRITION BY SEX AND SERVICE FY 1983 COHORT Attrition is...0.1 2 3 4 5-6 7-10 11-15 16.2 2i GAEYEARS OF SERVICE. ARMYRESRVE Y GADE RMYRESEVE Y YERS F SEVIC Pr~c:: r i~m ii0 50~~~~., -HT\\193 5 BLACK 18,626 40

How important is embeddedness in predicting Australian speech-language pathologists' intentions to leave their jobs and the profession?

PubMed

Heritage, Brody; Quail, Michelle; Cocks, Naomi

2018-03-05

This study explored the predictors of the outcomes of turnover and occupation attrition intentions for speech-language pathologists. The researchers examined the mediating effects of job satisfaction and strain on the relationship between stress and the latter outcomes. Additionally, the researchers examined the importance of embeddedness in predicting turnover intentions after accounting for stress, strain and job satisfaction. An online questionnaire was used to explore turnover and attrition intentions in 293 Australian speech-language pathologists. Job satisfaction contributed to a significant indirect effect on the stress and turnover intention relationship, however strain did not. There was a significant direct effect between stress and turnover intention after accounting for covariates. Embeddedness and the perceived availability of alternative jobs were also found to be significant predictors of turnover intentions. The mediating model used to predict turnover intentions also predicted occupation attrition intentions. The effect of stress on occupation attrition intentions was indirect in nature, the direct effect negated by mediating variables. Qualitative data provided complementary evidence to the quantitative model. The findings indicate that the proposed parsimonious model adequately captures predictors of speech-language pathologists' turnover and occupation attrition intentions. Workplaces and the profession may wish to consider these retention factors.

Factors related to attrition from trauma-focused cognitive behavioral therapy.

PubMed

Wamser-Nanney, Rachel; Steinzor, Cazzie E

2017-04-01

Attrition from child trauma-focused treatments such as Trauma-Focused Cognitive Behavioral Therapy (TF-CBT) is common; yet, the factors of children who prematurely terminate are unknown. The aim of the current study was to identify risk factors for attrition from TF-CBT. One hundred and twenty-two children (ages 3-18; M=9.97, SD=3.56; 67.2% females; 50.8% Caucasian) who received TF-CBT were included in the study. Demographic and family variables, characteristics of the trauma, and caregiver- and child-reported pretreatment symptoms levels were assessed in relation to two operational definitions of attrition: 1) clinician-rated dropout, and 2) whether the child received an adequate dose of treatment (i.e., 12 or more sessions). Several demographic factors, number of traumatic events, and children's caregiver-rated pretreatment symptoms were related to clinician-rated dropout. Fewer factors were associated with the adequate dose definition. Child Protective Services involvement, complex trauma exposure, and child-reported pretreatment trauma symptoms were unrelated to either attrition definition. Demographics, trauma characteristics, and level of caregiver-reported symptoms may help to identify clients at risk for premature termination from TF-CBT. Clinical and research implications for different operational definitions and suggestions for future work will be presented. Published by Elsevier Ltd.

Predictors of Attrition and Academic Success of Medical Students: A 30-Year Retrospective Study

PubMed Central

Maslov Kruzicevic, Silvija; Barisic, Katarina Josipa; Banozic, Adriana; Esteban, Carlos David; Sapunar, Damir; Puljak, Livia

2012-01-01

Aim To determine attrition and predictors of academic success among medical students at University of Split, Croatia. Methods We analysed academic records of 2054 students enrolled during 1979–2008 period. Results We found that 26% (533/2054) of enrolled students did not graduate. The most common reasons for attrition were ‘personal’ (36.4%), transfer to another medical school (35.6%), and dismissal due to unsatisfactory academic record (21.2%). Grade point average (GPA) and study duration of attrition students were significantly associated with parental education. There were 1126 graduates, 395 men and 731 women. Their average graduation GPA was 3.67±0.53 and study duration 7.6±2.44 years. During 5-year curriculum only 6.4% (42/654) of students graduated in time, and 55% (240/472) of students graduated in time after curriculum was extended to 6 years. Variables predicting whether a student will graduate or not were high school grades, entrance exam score and year of enrollment. Significant predictors of graduation grades were high school grades and entrance exam score. Entrance exam score predicted length of studying. Conclusion Preadmission academic qualifications and year of enrollment predict academic success in medical school. More attention should be devoted to high attrition. PMID:22737228

Attrition bias in a U.S. Internet survey of alcohol use among college freshmen.

PubMed

McCoy, Thomas P; Ip, Edward H; Blocker, Jill N; Champion, Heather; Rhodes, Scott D; Wagoner, Kimberly G; Mitra, Ananda; Wolfson, Mark

2009-07-01

Attrition bias is an important issue in survey research on alcohol, tobacco, and other drug use. The issue is even more salient for Internet studies, because these studies often have higher rates of attrition than face-to-face or telephone surveys, and there is limited research examining the issue in the field of drug usage, specifically for college underclassmen. This study assessed whether measures of high-risk drinking and alcohol-related consequences were related to attrition groups ("stayers" or "leavers") in a cohort of college freshmen. Data were collected in 2003 and 2004 from 2,144 first-year college students at 10 universities in the southeastern United States. Demographics, indicators of high-risk drinking, and alcohol-related consequences were compared between cohort stayers and leavers in statistical analyses using two methods. Analyses indicated that cohort leavers reported significantly higher levels of high-risk drinking (past-30-day heavy episodic drinking, weekly drunkenness) and past-30-day smoking but not significantly increased alcohol-related consequences. The directionality of bias was modestly consistent across outcomes and comparison methods. The current study's findings suggest that intervention efforts to reduce smoking or high-risk drinking need to consider attrition bias during study follow-up or account for it in analyses.

Attrition Bias in a U.S. Internet Survey of Alcohol Use Among College Freshmen*

PubMed Central

McCoy, Thomas P.; Ip, Edward H.; Blocker, Jill N.; Champion, Heather; Rhodes, Scott D.; Wagoner, Kimberly G.; Mitra, Ananda; Wolfson, Mark

2009-01-01

Objective: Attrition bias is an important issue in survey research on alcohol, tobacco, and other drug use. The issue is even more salient for Internet studies, because these studies often have higher rates of attrition than face-to-face or telephone surveys, and there is limited research examining the issue in the field of drug usage, specifically for college underclassmen. This study assessed whether measures of high-risk drinking and alcohol-related consequences were related to attrition groups (“stayers” or “leavers”) in a cohort of college freshmen. Method: Data were collected in 2003 and 2004 from 2,144 first-year college students at 10 universities in the southeastern United States. Demographics, indicators of high-risk drinking, and alcohol-related consequences were compared between cohort stayers and leavers in statistical analyses using two methods. Results: Analyses indicated that cohort leavers reported significantly higher levels of high-risk drinking (past-30-day heavy episodic drinking, weekly drunkenness) and past-30-day smoking but not significantly increased alcohol-related consequences. The directionality of bias was modestly consistent across outcomes and comparison methods. Conclusions: The current study's findings suggest that intervention efforts to reduce smoking or high-risk drinking need to consider attrition bias during study follow-up or account for it in analyses. PMID:19515302

Attrition due to orthopedic reasons during combat training: rates, types of injuries, and comparison between infantry and noninfantry units.

PubMed

Schwartz, Oren; Levinson, Tal; Astman, Nadav; Haim, Lavon

2014-08-01

The purpose of this study is to identify the prevalence and types of orthopedic injuries in infantry and noninfantry units responsible for attrition from combat training. 18,651 soldiers consecutively recruited to combat units (5 infantry and 4 noninfantry units) were included in this study. All recruited soldiers underwent and successfully passed a meticulous medical selection process. In all units, the soldiers participated in a suited fitness program that included marching, running, and strength training. Data were collected directly from attrite soldiers' files and detailed lists provided by the units' medical clinics. Out of 18,651 recruits, 641 (3.44%) attrite because of medical reasons. The leading cause of attrition was orthopedic diagnoses, and their overall rate was 43% (274 out of 641). Overuse injuries accounted for 90% of all orthopedic injuries. Low-back and lower extremity injuries accounted for 71.5% of all orthopedic injuries. There was high similarity in orthopedic injuries types and rates between infantry and noninfantry units. On the basis of our results, we recommend a multidisciplinary intense effort including physicians, physical training officers, physiotherapists, and commanders to significantly reduce overuse injuries, especially in the low-back and lower extremity regions. Reprint & Copyright © 2014 Association of Military Surgeons of the U.S.

Engagement and Nonusage Attrition With a Free Physical Activity Promotion Program: The Case of 10,000 Steps Australia.

PubMed

Guertler, Diana; Vandelanotte, Corneel; Kirwan, Morwenna; Duncan, Mitch J

2015-07-15

Data from controlled trials indicate that Web-based interventions generally suffer from low engagement and high attrition. This is important because the level of exposure to intervention content is linked to intervention effectiveness. However, data from real-life Web-based behavior change interventions are scarce, especially when looking at physical activity promotion. The aims of this study were to (1) examine the engagement with the freely available physical activity promotion program 10,000 Steps, (2) examine how the use of a smartphone app may be helpful in increasing engagement with the intervention and in decreasing nonusage attrition, and (3) identify sociodemographic- and engagement-related determinants of nonusage attrition. Users (N=16,948) were grouped based on which platform (website, app) they logged their physical activity: Web only, app only, or Web and app. Groups were compared on sociodemographics and engagement parameters (duration of usage, number of individual and workplace challenges started, and number of physical activity log days) using ANOVA and chi-square tests. For a subsample of users that had been members for at least 3 months (n=11,651), Kaplan-Meier survival curves were estimated to plot attrition over the first 3 months after registration. A Cox regression model was used to determine predictors of nonusage attrition. In the overall sample, user groups differed significantly in all sociodemographics and engagement parameters. Engagement with the program was highest for Web-and-app users. In the subsample, 50.00% (5826/11,651) of users stopped logging physical activity through the program after 30 days. Cox regression showed that user group predicted nonusage attrition: Web-and-app users (hazard ratio=0.86, 95% CI 0.81-0.93, P<.001) and app-only users (hazard ratio=0.63, 95% CI 0.58-0.68, P<.001) showed a reduced attrition risk compared to Web-only users. Further, having a higher number of individual challenges (hazard ratio=0.62, 95% CI 0.59-0.66, P<.001), workplace challenges (hazard ratio=0.94, 95% CI 0.90-0.97, P<.001), physical activity logging days (hazard ratio=0.921, 95% CI 0.919-0.922, P<.001), and steps logged per day (hazard ratio=0.99999, 95% CI 0.99998-0.99999, P<.001) were associated with reduced nonusage attrition risk as well as older age (hazard ratio=0.992, 95% CI 0.991-0.994, P<.001), being male (hazard ratio=0.85, 95% CI 0.82-0.89, P<.001), and being non-Australian (hazard ratio=0.87, 95% CI 0.82-0.91, P<.001). Compared to other freely accessible Web-based health behavior interventions, the 10,000 Steps program showed high engagement. The use of an app alone or in addition to the website can enhance program engagement and reduce risk of attrition. Better understanding of participant reasons for reducing engagement can assist in clarifying how to best address this issue to maximize behavior change.

Technology Insertion (TI)/Industrial Process Improvement (IPI) Task Order Number 1. Quick Fix Plan for WR-ALC, 7 RCC’s

DTIC Science & Technology

1989-09-25

Orders and test specifications. Some mandatory replacement of high failure items are directed by Technical Orders to extend MTBF. Precision bearing and...Experience is very high but natural attrition is reducing the numbers faster than training is furnishing younger mechanics. Surge conditions would be...model validation run output revealed that utilization of equipment is very low and manpower is high . Based on this analysis and the brainstorming

History of the U.S. Army Artillery and Missile School. Volume 4. 1958-1967

DTIC Science & Technology

1967-01-01

Graduates 367 155 Failures 10 1 Adrin Attrition e 0 Tu rnbacka 0 0 II 661 Vr 4 , • L4’,, i, • = i ’ .... • . .. . ., COB PORAL HANDLING EQUIPMENT...knowledge to assemble, install, adjust and perform organi- zational maintenance of on-missile electronic guidance control corn - ponents and systems...mechanic in an artillery unit (minimum experience may be waived for reserve corn - ponent personnel). Qualified as a driver and hold military vehicle

The Estimation of Lanchester Attrition-Rate Coefficients for an Aggregated Combat Model

DTIC Science & Technology

1976-06-01

34 This was the beginning of the war game as a serious -- miäui ..^.^.,,-..^„..-^■.■^■^-^..^■^■-^^^■-■■^^-■.^■.w^^,^^^^^.--1- ■ ■ .^.aiaaggijjMattajagaa...war games , assessments regarding tit effects of combat and other decisions were made subjectively by a control team of experienced military...single game , it is not a feasible mechanism for analyzing a broid spectrum of system alternatives in a responsive manner to meet planning cycle

Mastery inspired activities to help at risk students

NASA Astrophysics Data System (ADS)

Stelzer, Tim; Gladding, Gary; Gutmann, Brianne; Lundsgaard, Morten; Schroeder, Noah

2016-03-01

Introductory physics is a roadblock for many aspiring engineers at the University of Illinois. The overall attrition rate in our introductory mechanics and E&M courses is approximately 15%, however that rate doubles for some under-represented populations. We introduced a set of online activities designed to provide students both an accurate assessment of their current understanding, and the resources to improve their performance. This talk will describe the design of these activities, and their impact on student attitude and understanding.

Silicon as anode for high-energy lithium ion batteries: From molten ingot to nanoparticles

NASA Astrophysics Data System (ADS)

Leblanc, Dominic; Hovington, Pierre; Kim, Chisu; Guerfi, Abdelbast; Bélanger, Daniel; Zaghib, Karim

2015-12-01

In this work, we demonstrate that a new mechanical attrition process can be used to prepare nanosilicon powder from metallurgical grade silicon lumps. Composite Li-ion anode made from this nanometer-size powder was found to have a high reversible capacity of 2400 mAh g-1 and an improved cycling stability compared to micrometer-sized powder. It is proposed that improved battery cycling performance is ascribed to the nanoscale silicon particles which supresses the volume expansion owing to its superplasticity.

Job Design for Special Education Teachers

ERIC Educational Resources Information Center

Major, Amanda E.

2012-01-01

Special education teachers, especially those that teach students with behavioral/emotional challenges, have high attrition rates stemming from stress, job dissatisfaction, and low motivation. The external factors in the school setting and job contribute to special education teachers' attrition and disengagement. A relationship between motivation…

Pregnancy in the Navy: Impact on Absenteeism, Attrition, and Workgroup Morale.

DTIC Science & Technology

1978-09-01

impact of pregnancy on Navy absenteeism , attrition, and workgroup productivity and morale. Data were obtained by analyzing administrative records for...on workgroup productivity and morale. Further, if mandatory discharge for pregnancy were reinstated, it would decrease female absenteeism , increase

Suicidal thoughts and behaviors among college students and same-aged peers: results from the World Health Organization World Mental Health Surveys.

PubMed

Mortier, Philippe; Auerbach, Randy P; Alonso, Jordi; Axinn, William G; Cuijpers, Pim; Ebert, David D; Green, Jennifer G; Hwang, Irving; Kessler, Ronald C; Liu, Howard; Nock, Matthew K; Pinder-Amaker, Stephanie; Sampson, Nancy A; Zaslavsky, Alan M; Abdulmalik, Jibril; Aguilar-Gaxiola, Sergio; Al-Hamzawi, Ali; Benjet, Corina; Demyttenaere, Koen; Florescu, Silvia; De Girolamo, Giovanni; Gureje, Oye; Haro, Josep Maria; Hu, Chiyi; Huang, Yueqin; De Jonge, Peter; Karam, Elie G; Kiejna, Andrzej; Kovess-Masfety, Viviane; Lee, Sing; Mcgrath, John J; O'neill, Siobhan; Nakov, Vladimir; Pennell, Beth-Ellen; Piazza, Marina; Posada-Villa, José; Rapsey, Charlene; Viana, Maria Carmen; Xavier, Miguel; Bruffaerts, Ronny

2018-03-01

The primary aims are to (1) obtain representative prevalence estimates of suicidal thoughts and behaviors (STB) among college students worldwide and (2) investigate whether STB is related to matriculation to and attrition from college. Data from the WHO World Mental Health Surveys were analyzed, which include face-to-face interviews with 5750 young adults aged 18-22 spanning 21 countries (weighted mean response rate = 71.4%). Standardized STB prevalence estimates were calculated for four well-defined groups of same-aged peers: college students, college attriters (i.e., dropouts), secondary school graduates who never entered college, and secondary school non-graduates. Logistic regression assessed the association between STB and college entrance as well as attrition from college. Twelve-month STB in college students was 1.9%, a rate significantly lower than same-aged peers not in college (3.4%; OR 0.5; p < 0.01). Lifetime prevalence of STB with onset prior to age 18 among college entrants (i.e., college students or attriters) was 7.2%, a rate significantly lower than among non-college attenders (i.e., secondary school graduates or non-graduates; 8.2%; OR 0.7; p = 0.03). Pre-matriculation onset STB (but not post-matriculation onset STB) increased the odds of college attrition (OR 1.7; p < 0.01). STB with onset prior to age 18 is associated with reduced likelihood of college entrance as well as greater attrition from college. Future prospective research should investigate the causality of these associations and determine whether targeting onset and persistence of childhood-adolescent onset STB leads to improved educational attainment.

An Evaluation of Parent-Child Interaction Therapy With and Without Motivational Enhancement to Reduce Attrition.

PubMed

Webb, Haley J; Thomas, Rae; McGregor, Leanne; Avdagic, Elbina; Zimmer-Gembeck, Melanie J

2017-01-01

Although many interventions for child externalizing behavior report promising outcomes for families, high attrition prior to program completion remains a problem. Many programs report dropout rates of 50% or higher. In this trial we sought to reduce attrition and improve outcomes by augmenting a well-known evidence-based intervention, Parent-Child Interaction Therapy (PCIT), with a 3-session individual motivational enhancement component. Participants were 192 Australian caregivers (91.7% female; M age  = 34.4 years) and their children (33.3% female; M age  = 4.4 years). Families (51% referred from child welfare or health services for risk of maltreatment) were assigned to PCIT or a supported waitlist, with families assigned to PCIT receiving either standard PCIT (S/PCIT) or motivation-enhanced PCIT (M/PCIT), depending on their time of entry to the study. Waitlist families received phone calls every week for 12 weeks. Parents in M/PCIT reported more readiness to change their behavior from preassessment to after the motivation sessions. Also, parents who reported high, rather than low, motivation at preassessment did have a lower attrition rate, and there was some evidence that enhancing motivation was protective of premature attrition to the extent that caregivers achieved a high degree of change in motivation. Yet comparison of attrition rates and survival analyses revealed no difference between M/PCIT and S/PCIT in retention rate. Finally, there were greater reductions in externalizing and internalizing child behavior problems and parental stress among families in S/PCIT and M/PCIT compared with waitlist, and there was generally no significant difference between the two treatment conditions.

SUICIDAL THOUGHTS AND BEHAVIORS AMONG COLLEGE STUDENTS AND SAME-AGED PEERS: RESULTS FROM THE WORLD HEALTH ORGANIZATION WORLD MENTAL HEALTH SURVEYS

PubMed Central

MORTIER, PHILIPPE; AUERBACH, RANDY P.; ALONSO, JORDI; AXINN, WILLIAM G.; CUIJPERS, PIM; EBERT, DAVID D.; GREEN, JENNIFER G.; HWANG, IRVING; KESSLER, RONALD C.; LIU, HOWARD; NOCK, MATTHEW K.; PINDER-AMAKER, STEPHANIE; SAMPSON, NANCY A.; ZASLAVSKY, ALAN M.; ABDULMALIK, JIBRIL; AGUILAR-GAXIOLA, SERGIO; AL-HAMZAWI, ALI; BENJET, CORINA; DEMYTTENAERE, KOEN; FLORESCU, SILVIA; DE GIROLAMO, GIOVANNI; GUREJE, OYE; HARO, JOSEP MARIA; HU, CHIYI; HUANG, YUEQIN; DE JONGE, PETER; KARAM, ELIE G.; KIEJNA, ANDRZEJ; KOVESS-MASFETY, VIVIANE; LEE, SING; MCGRATH, JOHN J.; O’NEILL, SIOBHAN; NAKOV, VLADIMIR; PENNELL, BETH-ELLEN; PIAZZA, MARINA; POSADA-VILLA, JOSÉ; RAPSEY, CHARLENE; VIANA, MARIA CARMEN; XAVIER, MIGUEL; BRUFFAERTS, RONNY

2018-01-01

PURPOSE The primary aims are to (1) obtain representative prevalence estimates of suicidal thoughts and behaviors (STB) among college students worldwide and (2) investigate whether STB is related to matriculation to and attrition from college. METHODS Data from the WHO World Mental Health Surveys were analyzed, which include face-to-face interviews with 5,750 young adults aged 18–22 spanning 21 countries (weighted mean response rate = 71.4%). Standardized STB prevalence estimates were calculated for four well-defined groups of same-aged peers: college students, college attriters (i.e., dropouts), secondary school graduates who never entered college, and secondary school non-graduates. Logistic regression assessed the association between STB and college entrance as well as attrition from college. RESULTS Twelve-month STB in college students was 1.9%, a rate significantly lower than same-aged peers not in college (3.4%; OR=0.5; p<0.01). Lifetime prevalence of STB with onset prior to age 18 among college entrants (i.e., college students or attriters) was 7.2%, a rate significantly lower than among non-college attenders (i.e., secondary school graduates or non-graduates; 8.2%; OR=0.7; p=0.03). Pre-matriculation onset STB (but not post-matriculation onset STB) increased the odds of college attrition (OR=1.7; p<0.01). CONCLUSION STB with onset prior to age 18 is associated with reduced likelihood of college entrance as well as greater attrition from college. Future prospective research should investigate the causality of these associations and determine whether targeting onset and persistence of childhood-adolescent onset STB leads to improved educational attainment. PMID:29340781

A review of trends in attrition rates for surgical faculty: a case for a sustainable retention strategy to cope with demographic and economic realities.

PubMed

Satiani, Bhagwan; Williams, Thomas E; Brod, Heather; Way, David P; Ellison, E Christopher

2013-05-01

Our aim was to compare trends in retention of academic surgeons by reviewing surgical faculty attrition rates (leaving academic surgery for any reason) of 3 cohorts at 5-year intervals between 1996 and 2011. The Association of American Medical Colleges' Faculty Administrative Management On-Line User System database was queried for a retention report of all tenure/clinical track full-time MD faculty within our academic medical center on July 1, 1996 (group 1), July 1, 2001 (group 2), and July 1, 2006 (group 3). Retention was tracked for 5 years post snapshot. The individual 5-year cohort attrition rates (observed frequencies) were compared with combined attrition rates for all 3 groups (expected frequencies). Overall, attrition trends for groups 2 (lower) and 3 (higher) were significantly different than the trends for all groups combined. Minorities and professors at the full or associate rank in group 3 contributed to this difference. Faculty in group 3 leaving our academic medical center were significantly more likely to transition into nonacademic practice compared with the other 2 groups. Greater attrition in the last 5-year cohort, despite the increase in faculty positions, is worrisome. A continuous retention life cycle is critical if academic medical centers hope to compete for talent. Retention planning should include on-boarding programs for enculturation, monitoring of professional satisfaction, formalized mentoring of younger surgeons, retaining academic couples and a part-time workforce, leadership and talent management, exit interviews, and competitive financial packages. Copyright © 2013 American College of Surgeons. Published by Elsevier Inc. All rights reserved.

Grain size distribution of fault rocks: implication from natural gouges and high velocity friction experiments

NASA Astrophysics Data System (ADS)

Yang, X.; Chen, J.; Duan, B.

2011-12-01

The grain size distribution (GSD) is considered as an important parameter for the characterization of fault rocks. The relative magnitude of energy radiated as seismic waves to fracture energy plays a fundamental role to influence earthquake rupture dynamics. Currently, the details of grain size reduction mechanism and energy-budget are not well known. Here we present GSD measurements on fault rocks (gouge and breccias) in the main slip zone associated with the Wenchuan earthquake happened on 12 May, 2008, and on the gouges produced by high velocity friction (HVF) experiments. High velocity friction experiments were carried out on air dry granitic powder with grain size of 150 - 300 μm at normal stress of 1.0 MPa, a slip rate of 1.0 m / s and slip distances from 10 m to 30 m. On log-log plots of N(r) versus equivalent radius, two distinct linear parts can be discriminated with their intersection at 1 - 2 μm, defined as critical radius rc. One of power-law regime spans about 4 decades from 4 μm to 16 mm and the other covers a range of 0.2 - 2.0 μm. Larger fractal dimension from 2.7 to 3.5 are obtained for larger grain size regime, while lower values ranging from 1.7 to 2.1 for smaller size one. This two-stage distribution means the GSD is not self-similar (scale invariant) and the dominant ways of reducing grain size may be different from one another. XRD data show that the content of quartz drops greatly or disappears at 0.5 - 0.25 μm. GSD of HVF experimental products demonstrates similar feature to natural gouges. For instance, they all show the two-stage GSD with 1 - 2 μm of critical radius rc. The grains with their sizes of less than 1 μm appear rounded edges and equiaxial shapes. A variation in grain shapes can be observed in the grains larger than 5 μm. Some implications could be obtained from the measurements and experiments. (1) rc corresponds to the average value of grinding limit of rock-forming minerals. Further grain size reducing could be attributed to attrition during post-rupture processing such as steady-slip. (2) 90 % minerals with their sizes smaller than 0.5 μm is clays whose origin is neither associated with initially rupturing nor further grain attrition if we consider clay minerals within gouges as the products associated with fluid processes in inter-seismic intervals rather than by seismic slipping. (3) It is the grain that is created by the rupture process during earthquake could be used to calculate fracture energy. On the other hand, the grains forming in attrition during fault slip or / and inter-seismic intervals need to be picked out in order to get reasonable result. As example, if using D = 3.5 over the entire grain size range, the surface fracture energy will be over-estimated more than one order. Hence, surface fracture energy is a very small fraction in the total energy-budget of the earthquake.

Simulation of fluidized bed coal combustors

NASA Technical Reports Server (NTRS)

Rajan, R.

1979-01-01

The many deficiencies of previous work on simulation of fluidized bed combustion (FBC) processes are presented. An attempt is made to reduce these deficiencies, and to formulate a comprehensive FBC model taking into account the following elements: (1) devolatilization of coal and the subsequent combustion of volatiles and residual char; (2) sulfur dioxide capture by limestone; (3) NOx release and reduction of NOx by char; (4) attrition and elutriation of char and limestone; (5) bubble hydrodynamics; (6) solids mixing; (7) heat transfer between gas and solid, and solid and heat exchange surfaces; and (8) freeboard reactions.

Long-term release of antibiotics by carbon nanotube-coated titanium alloy surfaces diminish biofilm formation by Staphylococcus epidermidis.

PubMed

Hirschfeld, Josefine; Akinoglu, Eser M; Wirtz, Dieter C; Hoerauf, Achim; Bekeredjian-Ding, Isabelle; Jepsen, Søren; Haddouti, El-Mustapha; Limmer, Andreas; Giersig, Michael

2017-05-01

Bacterial biofilms cause a considerable amount of prosthetic joint infections every year, resulting in morbidity and expensive revision surgery. To address this problem, surface modifications of implant materials such as carbon nanotube (CNT) coatings have been investigated in the past years. CNTs are biologically compatible and can be utilized as drug delivery systems. In this study, multi-walled carbon nanotube (MWCNT) coated TiAl6V4 titanium alloy discs were fabricated and impregnated with Rifampicin, and tested for their ability to prevent biofilm formation over a period of ten days. Agar plate-based assays were employed to assess the antimicrobial activity of these surfaces against Staphylococcus epidermidis. It was shown that vertically aligned MWCNTs were more stable against attrition on rough surfaces than on polished TiAl6V4 surfaces. Discs with coated surfaces caused a significant inhibition of biofilm formation for up to five days. Therefore, MWCNT-modified surfaces may be effective against pathogenic biofilm formation on endoprostheses. Copyright © 2017 Elsevier Inc. All rights reserved.

Personal, Situational, and Organizational Determinants of Navy Enlisted Attrition

DTIC Science & Technology

1980-06-01

of regular high school instruction. The GED test battery contains five testsz writing skills, social studies, science, reading skills, and mathematics ...expanded apprentice train- ing program for airmen and seamen might, ceteris paribus, bring the GENDET attrition rate closer to acceptable lvels . 13 ] KN

Attrition of Hmong Students in Teacher Education Programs.

ERIC Educational Resources Information Center

Root, Steven; Rudawski, Anthony; Taylor, Matthew; Rochon, Ronald

2003-01-01

A descriptive study addressed student attrition in two Title VII Bilingual Education Career Ladder Programs for Hmong paraprofessionals and traditional-age college students working toward teacher certification in Wisconsin. Surveys showed that dropouts were disproportionately male and nontraditional students; factors included financial problems,…

Attrition resistant gamma-alumina catalyst support

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singleton, Alan H.; Oukaci, Rachid; Goodwin, James G.

2006-03-14

A .gamma.-alumina catalyst support having improved attrition resistance produced by a method comprising the steps of treating a particulate .gamma.-alumina material with an acidic aqueous solution comprising water and nitric acid and then, prior to adding any catalytic material thereto, calcining the treated .gamma.-alumina.

Process Improvement: Addressing Attrition from the Uniformed Services University of the Health Sciences Nurse Anesthesia Program.

PubMed

Wilson, John Tyler; Gibbons, Susanne W; Wofford, Kenneth

2015-10-01

This retrospective cohort study examined the Uniformed Services University of the Health Sciences Registered Nurse Anesthesia program to identify reasons for high attrition rates. Relevant data were examined for 180 students enrolled in classes from 2005 through 2011. During that period, 40 students were dismissed or disenrolled, with the highest attrition rate (35%) occurring in the class of 2010. Evidence from this investigation indicates students who completed the program were younger, earned higher grade point averages while completing their undergraduate bachelor of science in nursing, and achieved higher analytic and total Graduate Record Examination scores than did students who withdrew or were dismissed. Gender differences were noted, as a greater proportion of women completed the program compared with men. Personal, family, and other issues frequently overlapped, with academic performance problems leading to attrition. Based on these findings, a number of important changes were made in the admission process to the USUHS RNA program and in the nonacademic mentoring and assistance offered to students.

Medical waivers for atopic conditions did not affect attrition among U.S. military academy cadets.

PubMed

Teague, Nathan; Wiesen, Andrew

2011-01-01

Atopic conditions account for approximately 35% of medical disqualifications among West Point applicants each year. There are limited outcome data concerning the utility of the atopic disqualification standards in predicting military success. Cadets entering the United States Military Academy (USMA) from 2001-2004 were selected as the cohort for this study. They were classified as exposed (medical waiver for an atopic condition) and unexposed (no medical waiver) and followed throughout their enrollment at the USMA. The outcome measures were attrition from school and frequency of clinic visits. After adjusting for gender and age, waiver status was not associated with attrition (OR = 1.02) but was associated with an increased odds of being a high clinic user (OR = 1.37). Time-to-event analysis found an equal risk of attrition between the groups over time (HR = 1.03). Relaxing atopic disqualification standards will not increase the drop-out rate from the USMA, but may increase clinic utilization.

Attrition during a randomized controlled trial of reduced nicotine content cigarettes as a proxy for understanding acceptability of nicotine product standards.

PubMed

Mercincavage, Melissa; Wileyto, E Paul; Saddleson, Megan L; Lochbuehler, Kirsten; Donny, Eric C; Strasser, Andrew A

2017-06-01

To determine (1) if nicotine content affects study attrition-a potential behavioral measure of acceptability-in a trial that required compliance with three levels of reduced nicotine content (RNC) cigarettes, and (2) if attrition is associated with subjective and behavioral responses to RNC cigarettes. Secondary analysis of a 35-day, parallel-design, open-label, randomized controlled trial. After a 5-day baseline period, participants were randomized to smoke for three 10-day periods: their preferred brand (control group) or RNC cigarettes with three nicotine levels in a within-subject stepdown (one group: high-moderate-low) or non-stepdown (five groups: high-low-moderate, low-moderate-high, low-high-moderate, moderate-low-high, moderate-high-low) fashion. A single site in Philadelphia, PA, USA. A total of 246 non-treatment-seeking daily smokers [mean age = 39.52, cigarettes per day (CPD) = 20.95, 68.3% white] were recruited from October 2007 to June 2013. The primary outcome was attrition. Key predictors were nicotine content transition and study period. Exploratory predictors were taste and strength subjective ratings, total puff volume and carbon monoxide (CO) boost. Covariates included: age, gender, race, education and nicotine dependence. Overall attrition was 31.3% (n = 77): 24.1% of the control and 25.0% of the stepdown RNC cigarette groups dropped out versus 44.6% of non-stepdown groups (P = 0.006). Compared with controls, attrition odds were 4.5 and 4.7 times greater among smokers transitioning from preferred and the highest RNC cigarettes to the lowest RNC cigarettes, respectively (P = 0.001 and 0.003). Providing more favorable initial taste ratings of study cigarettes decreased attrition odds by 2% (P = 0.012). The majority of participants completed a 35-day trial of varying levels of reduced nicotine content cigarettes. Participant dropout was greater for cigarettes with lower nicotine content and less in smokers reporting more favorable subjective ratings of the cigarettes. © 2017 Society for the Study of Addiction.

Identification of cognitive and non-cognitive predictive variables related to attrition in baccalaureate nursing education programs in Mississippi

NASA Astrophysics Data System (ADS)

Hayes, Catherine

2005-07-01

This study sought to identify a variable or variables predictive of attrition among baccalaureate nursing students. The study was quantitative in design and multivariate correlational statistics and discriminant statistical analysis were used to identify a model for prediction of attrition. The analysis then weighted variables according to their predictive value to determine the most parsimonious model with the greatest predictive value. Three public university nursing education programs in Mississippi offering a Bachelors Degree in Nursing were selected for the study. The population consisted of students accepted and enrolled in these three programs for the years 2001 and 2002 and graduating in the years 2003 and 2004 (N = 195). The categorical dependent variable was attrition (includes academic failure or withdrawal) from the program of nursing education. The ten independent variables selected for the study and considered to have possible predictive value were: Grade Point Average for Pre-requisite Course Work; ACT Composite Score, ACT Reading Subscore, and ACT Mathematics Subscore; Letter Grades in the Courses: Anatomy & Physiology and Lab I, Algebra I, English I (101), Chemistry & Lab I, and Microbiology & Lab I; and Number of Institutions Attended (Universities, Colleges, Junior Colleges or Community Colleges). Descriptive analysis was performed and the means of each of the ten independent variables was compared for students who attrited and those who were retained in the population. The discriminant statistical analysis performed created a matrix using the ten variable model that was able to correctly predicted attrition in the study's population in 77.6% of the cases. Variables were then combined and recombined to produce the most efficient and parsimonious model for prediction. A six variable model resulted which weighted each variable according to predictive value: GPA for Prerequisite Coursework, ACT Composite, English I, Chemistry & Lab I, Microbiology & Lab I, and Number of Institutions Attended. Results of the study indicate that it is possible to predict attrition among students enrolled in baccalaureate nursing education programs and that additional investigation on the subject is warranted.

Colloidal approach to dispersion and enhanced deaggregation of aqueous ferrite suspensions

NASA Astrophysics Data System (ADS)

Mandanas, Michael Patrick M.

The role of solution and surface chemistry on deaggregation of calcined ferrites during attrition (stirred-media) milling of aqueous suspensions were investigated. Suspensions of commercially calcined Fe2O 3 powder (d50 ˜ 5.0 mum) were milled at different solid loadings and suspension pH. The drift of suspension pH, from pH 2.5 to pH 7.0, during solid loading experiments accounted for the observed reagglomeration with milling time. The observed deaggregation rates during pH stat milling, in the acidic region, can be related to (i) elevated solubility and (ii) enhanced dispersion via surface charge. Proton adsorption density during pH stat milling at different pH values is also comparable to existing potentiometric titration plots and can be related to deaggregation rates. A passivation-dispersion approach for dispersing manganese zinc ferrite (MnxZn(1 - x)Fe2O4) powder is presented. Addition of oxalic acid can help control dissolution reactions from particle surfaces and is subsequently dispersed with polyethyleneimine (PEI). Fully dissociated oxalic acid (pK1 = 1.2, pK2 = 4.3) solutions reacted with MnxZn(1 - x)Fe 2O4 leads to the formation of a uniform negative charge on the particle surface, resulting from the sparingly soluble salt formed on the surface. The resulting rheological data for passivation/dispersion of relatively high solid MnxZn(1 - x)Fe2O 4 suspensions (˜80 w/o, (˜40 v/o)) demonstrate improved colloid stability with improved rheological properties. Using the passivation dispersion scheme developed, deaggregation of commercially calcined MnxZn(1 - x)Fe2O4 powders during attrition milling was investigated. Reagglomeration is apparent when using a typical treatment, 2 w/w of a sulfonated based naphthalene condensate, during deaggregation of the calcined MnxZn(1 - x)Fe 2O4. However, is not observed for select oxalate/PEI treatments. The determined ideal treatment is 2 w/w oxalate and 3 w/w PEI based on the particle size and rheological characteristics of the suspensions during milling. (Abstract shortened by UMI.)

Lead optimization attrition analysis (LOAA): a novel and general methodology for medicinal chemistry.

PubMed

Munson, Mark; Lieberman, Harvey; Tserlin, Elina; Rocnik, Jennifer; Ge, Jie; Fitzgerald, Maria; Patel, Vinod; Garcia-Echeverria, Carlos

2015-08-01

Herein, we report a novel and general method, lead optimization attrition analysis (LOAA), to benchmark two distinct small-molecule lead series using a relatively unbiased, simple technique and commercially available software. We illustrate this approach with data collected during lead optimization of two independent oncology programs as a case study. Easily generated graphics and attrition curves enabled us to calibrate progress and support go/no go decisions on each program. We believe that this data-driven technique could be used broadly by medicinal chemists and management to guide strategic decisions during drug discovery. Copyright © 2015 Elsevier Ltd. All rights reserved.

Quantitative evaluation of dental abfraction and attrition using a swept-source optical coherence tomography system.

PubMed

Marcauteanu, Corina; Bradu, Adrian; Sinescu, Cosmin; Topala, Florin Ionel; Negrutiu, Meda Lavinia; Podoleanu, Adrian Gh

2014-02-01

A fast swept-source optical coherence tomography (SS-OCT) system is employed to acquire volumes of dental tissue, in order to monitor the temporal evolution of dental wear. An imaging method is developed to evaluate the volume of tissue lost in ex vivo artificially induced abfractions and attritions. The minimal volume (measured in air) that our system could measure is 2352 μm3. A volume of 25,000 A-scans is collected in 2.5 s. All these recommend the SS-OCT method as a valuable tool for dynamic evaluation of the abfraction and attrition with remarkable potential for clinical use.

A sex comparison of reasons for attrition of non-journeyman FAA air traffic controllers.

DOT National Transportation Integrated Search

1974-03-01

Recent ATC attrition rates showed no sex differences in the proportion of trainees who completed FAA Academy training; however, the percentage of females who subsequently left ATC work was over twice that of male trainees. In the present study, the 5...

Supportive Induction Slows the Revolving Door

ERIC Educational Resources Information Center

Wilkinson, Gayle A.

2009-01-01

The revolving door appropriately describes the attrition among beginning teachers. Especially high attrition plagues our urban schools where highly qualified teachers are most crucial. Even though research over 3 decades has provided the basis for intricate induction programs, not all new teachers experience them. Effective mentoring has provided…

Beginning English Teacher Attrition, Mobility, and Retention

ERIC Educational Resources Information Center

Hahs-Vaughn, Debbie L.; Scherff, Lisa

2008-01-01

Although much research on teacher attrition and mobility exists, few researchers have addressed English teachers specifically. The present authors, using the 1999-2000 Schools and Staffing Survey (SASS) and the Teacher Follow-Up Survey (TFS; National Center for Education Statistics, 2005) examined individual and school characteristics and…

ATTRITION RATE STUDY.

ERIC Educational Resources Information Center

HANSEN, M. DUANE; WENZEL, GUSTAVE G.

INSTEAD OF FOCUSING ON STUDENT CHARACTERISTICS, AS DO MOST DROPOUT STUDIES, THIS ONE (1) CONSIDERS SPECIFIC INSTITUTIONAL CHARACTERISTICS OF GRADING PRACTICES, (2) ANALYZES THESE PRACTICES WITHIN A GIVEN TERM INSTEAD OF OVER SEVERAL YEARS, AND (3) BROADENS THE DEFINITION OF ATTRITION TO INCLUDE BOTH FAILURE AND WITHDRAWAL. IT ATTEMPTS TO IDENTIFY…

Instrument Development for Examining Student Attrition

ERIC Educational Resources Information Center

McRoberts, Timothy J.; Miller, Tess

2015-01-01

Instruments designed to track student changes in higher education are essential for monitoring program development in competitive higher education markets. As part of a developmental evaluation, a student questionnaire was developed and piloted to examine attrition rates in college programs. The purpose of the questionnaire was to explore factors…

Predicting Student Attrition with Data Mining Methods

ERIC Educational Resources Information Center

Delen, Dursun

2012-01-01

Affecting university rankings, school reputation, and financial well-being, student retention has become one of the most important measures of success for higher education institutions. From the institutional perspective, improving student retention starts with a thorough understanding of the causes behind the attrition. Such an understanding is…

The attrition condition: use of a preparatory course to reduce EMT course attrition and improve performance on North Carolina certification exams.

PubMed

Renkiewicz, Ginny K; Hubble, Michael W

2015-01-01

A growing concern in emergency medical services (EMS) education is student attrition. Perchance, there is a population of nonmatriculate students lacking prerequisite academic skills or who are otherwise ill prepared for the unique requirements of the EMS profession. Consequently, addressing these issues could promote academic and occupational preparedness, thereby reducing emergency medical technician (EMT) course attrition. To measure the impact of a preparatory course designed to address academic and psychosocial skills affecting EMT course completion. We conducted a retrospective analysis of a 24-hour preparatory course using a before-and-after nonexperimental design. The course included the EMT preparatory curriculum, program orientation, work-force-preparedness skills, and an academic skills assessment. All students who were enrolled in an EMT course at a single study site between July 2008 and December 2011 were included. Chi-square analysis was performed on attrition categories defined by CoAEMSP (Academic, Disciplinary, Attendance, Health, Financial, Personal, Never Attended) and state exam categories (Airway, Medical, Trauma, Operations, Pediatrics, Preparatory, Assessment). A logistic regression model calculated the odds ratio (OR) of course completion as a function of preparatory course completion while controlling for demography. The historical control group consisted of 117 (58.5%) students enrolled prior to implementation of the preparatory course, while the remaining 83 (41.5%) students in the intervention group completed the course. Overall attrition was 115 (57.5%) students, with lower rates observed in the intervention group (32.5 vs. 75.2%, p < 0.01). Among noncompleters, the majority originated from the control groups in attrition categories of Academic (4.8 vs. 39.3%, p < 0.01) and Never Attended (1.2 vs. 14.5%, p < 0.01). Students who took the preparatory course were more likely to achieve course completion (OR = 5.17, p < 0.01). The use of the preparatory course produced a higher first-time test-taker pass rate despite showing little difference in individual categories. Students who participated in an EMS preparatory course were 5 times more likely to achieve course completion and perform higher on most portions of the state exam; and the proportion of students that enrolled but never attended an EMT course was reduced. Unlike prior studies, we did not observe a paradoxical increase in other attrition categories after addressing academic preparedness. These findings may prove useful for EMS educators tasked with program planning.

Increased prevalence of pregnancy and comparative risk of program attrition among individuals starting HIV treatment in East Africa.

PubMed

Holmes, Charles B; Yiannoutsos, Constantin T; Elul, Batya; Bukusi, Elizabeth; Ssali, John; Kambugu, Andrew; Musick, Beverly S; Cohen, Craig; Williams, Carolyn; Diero, Lameck; Padian, Nancy; Wools-Kaloustian, Kara K

2018-01-01

The World Health Organization now recommends initiating all pregnant women on life-long antiretroviral therapy (ART), yet there is limited information about the characteristics and program outcomes of pregnant women already on ART in Africa. Our hypothesis was that pregnant women comprised an increasing proportion of those starting ART, and that sub-groups of these women were at higher risk for program attrition. We used the International Epidemiology Databases to Evaluate AIDS- East Africa (IeDEA-EA) to conduct a retrospective cohort study including HIV care and treatment programs in Kenya, Uganda, and Tanzania. The cohort consecutively included HIV-infected individuals 13 years or older starting ART 2004-2014. We examined trends over time in the proportion pregnant, their characteristics and program attrition rates compared to others initiating and already receiving ART. 156,474 HIV-infected individuals (67.0% women) started ART. The proportion of individuals starting ART who were pregnant women rose from 5.3% in 2004 to 12.2% in 2014. Mean CD4 cell counts at ART initiation, weighted for annual program size, increased from 2004 to 2014, led by non-pregnant women (annual increase 20 cells/mm3) and men (17 cells/mm3 annually), with lower rates of change in pregnant women (10 cells/mm3 per year) (p<0.0001). There was no significant difference in the cumulative incidence of program attrition at 6 months among pregnant women starting ART and non-pregnant women. However, healthy pregnant women starting ART (WHO stage 1/2) had a higher rate of attrition rate (9.6%), compared with healthy non-pregnant women (6.5%); in contrast among women with WHO stage 3/4 disease, pregnant women had lower attrition (8.4%) than non-pregnant women (14.4%). Among women who initiated ART when healthy and remained in care for six months, subsequent six-month attrition was slightly higher among pregnant women at ART start (3.5%) compared to those who were not pregnant (2.4%), (absolute difference 1.1%, 95% CI 0.7%-1.5%). Pregnant women comprise an increasing proportion of those initiating ART in Africa, and pregnant women starting ART while healthy are at higher risk for program attrition than non-pregnant women. As ART programs further expand access to healthier pregnant women, further studies are needed to better understand the drivers of loss among this high risk group of women to optimize retention.

Consequences of an Extended Recruitment on Participation in the Follow-Up of a Child Study: Results from the German IDEFICS Cohort.

PubMed

Langeheine, Malte; Pohlabeln, Hermann; Ahrens, Wolfgang; Rach, Stefan

2017-01-01

Declining response proportions in population-based studies are often countered by extended recruitment efforts at baseline that may, however, result in higher attrition in a subsequent follow-up. This study analysed the effect of extended recruitment efforts on attrition at the first follow-up of a child cohort. We used paradata (i.e. information about the process of data collection) from the German IDEFICS cohort investigating dietary- and life style-induced health effects on children to quantify recruitment effort and classify respondents as completing the recruitment early vs. late for baseline and follow-up separately. Multilevel logistic regression models were used to investigate the association between recruitment effort and attrition at follow-up (loss to follow-up) adjusted for sociodemographic and health related variables. Individuals who were late respondents at baseline and early respondents at the follow-up had a higher chance of attrition (odds ratio 1.65, 95% confidence interval (CI) 1.19, 2.28) as compared to other groups. An investigation of reasons for non-participation revealed that members of this group were more likely to be not reachable by phone. An extended recruitment effort at baseline of a child cohort study is not per se associated with a higher chance of attrition at follow-up. Much care should be taken to collect valid telephone numbers. © 2016 John Wiley & Sons Ltd.

Methods to Limit Attrition in Longitudinal Comparative Effectiveness Trials: Lessons from the Lithium Use for Bipolar Disorder (LiTMUS) Study

PubMed Central

Sylvia, Louisa G.; Reilly-Harrington, Noreen A.; Leon, Andrew C.; Kansky, Christine I.; Ketter, Terence A.; Calabrese, Joseph R.; Thase, Michael E.; Bowden, Charles L.; Friedman, Edward S.; Ostacher, Michael J.; Iosifescu, Dan V.; Severe, Joanne; Nierenberg, Andrew A.

2013-01-01

Background High attrition rates which occur frequently in longitudinal clinical trials of interventions for bipolar disorder limit the interpretation of results. Purpose The aim of this article is to present design approaches that limited attrition in the Lithium Use for Bipolar Disorder (LiTMUS) Study. Methods LiTMUS was a 6-month randomized, longitudinal multi-site comparative effectiveness trial that examined bipolar participants who were at least mildly ill. Participants were randomized to either low to moderate doses of lithium or no lithium, in addition to other treatments needed for mood stabilization administered in a guideline-informed, empirically supported, and personalized fashion (N=283). Results Components of the study design that may have contributed to the low attrition rate of the study included use of: (1) an intent-to-treat design; (2) a randomized adjunctive single-blind design; (3) participant reimbursement; (4) intent-to-attend the next study visit (includes a discussion of attendance obstacles when intention is low); (5) quality care with limited participant burden; and (6) target windows for study visits. Limitations Site differences and the effectiveness and tolerability data have not been analyzed yet. Conclusions These components of the LiTMUS study design may have reduced the probability of attrition which would inform the design of future randomized clinical effectiveness trials. PMID:22076437

Attrition, burnout, job dissatisfaction and occupational therapy managers.

PubMed

Kraeger, M M; Walker, K F

1992-01-01

At a time when there is growing concern about the person-power shortages in occupational therapy, there is a need to address reasons why therapists leave the job market. Two job-related reasons for attrition are burnout and job dissatisfaction. The burnout phenomenon occurs as a result of personnel shortages, high-stress demands on therapists, the severity and complexity of client's problems, and the therapist's own ''worker personality.'' Bureaucratic constraints, limited advancement, issues related to a profession which is made up predominantly of women, lack of autonomy, and type of management and supervision are factors that contribute to job dissatisfaction. Occupational therapy managers can consider the causes of burnout and job dissatisfaction and initiate resources to retain therapists. Managers can increase the job benefits, such as flexible working hours, take steps to reduce stress in the workplace, offer career laddering opportunities, and promote staff development. By identifying the causes for attrition and by addressing those causes, the threat of losing therapists from the work force may be averted. Respondents (n = 106) to a survey of occupational therapy managers indicated that job dissatisfaction, burnout, and attrition of registered occupational therapists were not major problems in their settings. They reported a variety of strategies to reduce job dissatisfaction, burnout, and attrition. When these problems were present, managers cited bureaucratic red tape, lack of opportunity for advancement, and increasing role demands as contributing factors.

Evolutionary dynamics of a smoothed war of attrition game.

PubMed

Iyer, Swami; Killingback, Timothy

2016-05-07

In evolutionary game theory the War of Attrition game is intended to model animal contests which are decided by non-aggressive behavior, such as the length of time that a participant will persist in the contest. The classical War of Attrition game assumes that no errors are made in the implementation of an animal׳s strategy. However, it is inevitable in reality that such errors must sometimes occur. Here we introduce an extension of the classical War of Attrition game which includes the effect of errors in the implementation of an individual׳s strategy. This extension of the classical game has the important feature that the payoff is continuous, and as a consequence admits evolutionary behavior that is fundamentally different from that possible in the original game. We study the evolutionary dynamics of this new game in well-mixed populations both analytically using adaptive dynamics and through individual-based simulations, and show that there are a variety of possible outcomes, including simple monomorphic or dimorphic configurations which are evolutionarily stable and cannot occur in the classical War of Attrition game. In addition, we study the evolutionary dynamics of this extended game in a variety of spatially and socially structured populations, as represented by different complex network topologies, and show that similar outcomes can also occur in these situations. Copyright © 2016 Elsevier Ltd. All rights reserved.

Limestone calcination under calcium-looping conditions for CO2 capture and thermochemical energy storage in the presence of H2O: an in situ XRD analysis.

PubMed

Valverde, Jose Manuel; Medina, Santiago

2017-03-15

This work reports an in situ XRD analysis of whether the calcination/carbonation behavior of natural limestone (CaCO 3 ) is affected by the addition of H 2 O to the calciner at a very low concentration under relevant Calcium-Looping (CaL) conditions for CO 2 capture in coal fired power plants (CFPP) and Thermochemical Energy Storage (TCES) in Concentrated Solar Power plants (CSP). Previous studies have demonstrated that the presence of steam in the calciner at a high concentration yields a significant increase in the reaction rate. However, a further undesired consequence is the serious deterioration of the CaO mechanical strength, which would lead to particle attrition and mass loss in any CaL process based on the use of circulating fluidized beds. The results presented in this manuscript on the time evolution of the wt% and crystallite size of the phases involved in the calcination/carbonation reactions indicate that the calcination rate is still notably increased by the presence of H 2 O at very low concentrations whereas the reactivity toward carbonation and crystal structure of the formed CaO are not essentially affected, which suggests that the CaO mechanical strength is not impaired. Thus, the benefit of using steam for calcination in the CaL process could be still retained while at the same time particle attrition would not be promoted.

Attrition in Psychotherapy: A Survival Analysis

ERIC Educational Resources Information Center

Roseborough, David John; McLeod, Jeffrey T.; Wright, Florence I.

2016-01-01

Purpose: Attrition is a common problem in psychotherapy and can be defined as clients ending treatment before achieving an optimal response. Method: This longitudinal, archival study utilized data for 3,728 clients, using the Outcome Questionnaire 45.2. A Cox regression proportional hazards (hazard ratios) model was used in order to better…

Attrition from Student Affairs: Perspectives from Those Who Exited the Profession

ERIC Educational Resources Information Center

Marshall, Sarah M.; Gardner, Megan Moore; Hughes, Carole; Lowery, Ute

2016-01-01

Attrition of student affairs professionals is an issue of concern for the profession. This mixed methods study highlights reasons why participants left their student affairs careers. Seven general themes emerged from the study, including burnout, salary issues, career alternatives, work/family conflict, limited advancement, supervisor issues and…

Expatriate Executive Failure: An Overview of the Underlying Causes.

ERIC Educational Resources Information Center

Rankis, Olaf E.; Beebe, Steven A.

The high attrition rate among North American expatriate executives has become a significant problem for firms doing business in foreign countries. A review of the literature reveals a number of factors contributing to attrition, including culture shock, family problems, managerial style and practice differences, insensitivity to host cultures, and…

"Managed" Teacher Turnover: A Strategy for School Improvement

ERIC Educational Resources Information Center

Lewis, Jessica L.; London, Tim D.

2009-01-01

Given the negative implications of unmanaged teacher attrition for student learning and the potential of leadership actions to affect this dynamic, this article highlights the practices of one principal in the Chicago Public School (CPS) system who used teacher attrition to her school's advantage. Her actions reveal leadership practices that can…

Student Attrition in Mathematics E-Learning

ERIC Educational Resources Information Center

Smith, Glenn Gordon; Ferguson, David

2005-01-01

Qualitative studies indicate that mathematics does not work well in e-learning. The current study used quantitative methods to investigate more objectively the extent of problems with mathematics in e-learning. The authors used student attrition as a simple measure of student satisfaction and course viability in two studies, one investigating…

Satisfaction among Current Doctoral Students in Special Education

ERIC Educational Resources Information Center

Wasburn-Moses, Leah

2008-01-01

Despite the growing demand for professionals with doctoral degrees in special education, doctoral programs are not producing enough graduates to fulfill this need. Although large attrition rates exist in doctoral study across discipline, very little is known about the attrition or satisfaction of doctoral students in special education. This…

Development of the Student Expectations of Online Learning Survey (SEOLS): A Pilot Study

ERIC Educational Resources Information Center

Harris, Sandra M.; Larrier, Yvonne I.; Castano-Bishop, Marianne

2011-01-01

The problem of attrition in online learning has drawn attention from distance education administrators and chief academic officers of higher education institutions. Many studies have addressed factors related to student attrition, persistence and retention in online courses. However, few studies have examined how student expectations influence…

Institutional Bonding.

ERIC Educational Resources Information Center

Allard, M. June

Institutional bonding was examined at a public, urban commuter college with exceptionally high attrition and visibly low morale. Changes in bonding and attrition were measured 6 years after a 2-year effort to develop school identity and student feelings of membership. It was found that a simple index of campus morale is provided by level of…

Insights into Attrition from University-Based Enabling Programs

ERIC Educational Resources Information Center

Bookallil, Cheryl; Harreveld, Bobby

2017-01-01

High attrition rates from university-based enabling programs continue to be the subject of much research and administrative effort. Understanding the factors behind decisions to withdraw from such programs is difficult since those who do not successfully complete an enabling program may not readily agree to participate in research into their…

Reciprocal Mentoring: Can it Help Prevent Attrition for Beginning Teachers?

ERIC Educational Resources Information Center

Paris, Lisa F.

2013-01-01

Forty per cent of new teachers in Australia leave the profession in the first five years (Ingersoll, 2012; Watt & Richardson, 2011; Hartsuyker, 2007). Stress, induction failure and professional isolation have been identified as key attrition factors. Mentoring has been used both internationally and in Australia to enhance induction and…

Factors That Influence Student Attrition in Online Courses

ERIC Educational Resources Information Center

Shaw, Melanie; Burrus, Scott; Ferguson, Karen

2016-01-01

Research was conducted to explore predictors for online higher education student attrition. This research was conducted using results from the SmarterMeasure Learning Readiness Indicator to track students in their degree programs. In addition, student outreach was conducted with an experimental group of at-risk students to determine if additional…

Early Intervention: Using Assessment to Reduce Student Attrition

ERIC Educational Resources Information Center

Vander Schee, Brian A.

2011-01-01

The number of studies conducted on college-student attrition is overwhelming. But few examine the impact of adding an early-intervention assessment tool to existing retention programs. Too often, colleges and universities conduct initiatives with similar purposes as disconnected efforts; retention programs in particular can benefit from a more…

First Language Attrition

ERIC Educational Resources Information Center

Schmid, Monika S.

2016-01-01

Language attrition research has developed in several clearly delimited phases spanning, roughly, each of the three decades between 1982 and 2012 (see Kopke & Schmid 2004 for a more detailed overview and analysis). The first phase was an era of stocktaking, with a number of symposia, collected volumes and special issues of journals. All of…

Do We Give Them a Fair Chance? Attrition among First-Year Tertiary Students

ERIC Educational Resources Information Center

Whitehead, David

2012-01-01

International research suggests that government policy, institutional culture and learner characteristics influence the attrition rate of first-year tertiary education students. These variables were investigated in relation to a cohort of 21 New Zealand students who failed a core literacy paper. The research utilised questionnaires, interviews…

Correlates of Military Satisfaction and Attrition Among Army Personnel.

ERIC Educational Resources Information Center

Allen, John P.; Bell, D. Bruce

A study determined relationships between Army organizational variables and levels of soldier satisfaction and assessed correlates of attrition and battalion effectiveness ratings. It was based on a secondary analysis of data collected in the Army Life-78 Study, which considered relationships of organizational climate and unit effectiveness.…

Factors Associated with Attrition in Weight Loss Programs

ERIC Educational Resources Information Center

Grave, Riccardo Dalle; Suppini, Alessandro; Calugi, Simona; Marchesini, Giulio

2006-01-01

Attrition in weight loss programs is a complex process, influenced by patients' pretreatment characteristics and treatment variables, but available data are contradictory. Only a few variables have been confirmed by more than one study as relevant risk factors, but recently new data of clinical utility emerged from "real world" large observational…

Searching for Satisfaction: Black Female Teachers' Workplace Climate and Job Satisfaction

ERIC Educational Resources Information Center

Farinde-Wu, Abiola; Fitchett, Paul G.

2018-01-01

Job satisfaction may decrease teacher attrition. Furthermore, job satisfaction correlates with teacher retention, which may influence school building climate and student achievement. Potentially affecting students' progress and seeking to reduce attrition rates among Black teachers, this quantitative study uses data from the 2007-2008 Schools and…

Factors That Influence the Attrition of Mentors in Rural Areas

ERIC Educational Resources Information Center

Givens, Sharon Leenese

2012-01-01

This research is a qualitative case study exploring the factors that influence the attrition of mentors in rural areas. Mentoring initiatives and programs have proliferated throughout schools in an effort to provide students with positive role models, increase graduation rates and improve overall performance Mentoring programs are an increasingly…

Stepping up Support for New Teachers

ERIC Educational Resources Information Center

Moore, Alicia

2016-01-01

New teacher attrition is a serious problem, with some studies estimating that 50 percent of teachers leave the profession within their first few years. This high attrition rate means that many schools have large number of inexperienced teachers and that districts must spend scarce funds for recruitment and replacement costs. Springfield Public…

Management of Tooth Surface Loss of Varying Etiology with Full Mouth all Ceramic Computer-Aided Design/Computer-Aided Manufacture Restorations.

PubMed

Bettie, Nirmal Famila; Kandasamy, Saravanan; Prasad, Venkat

2017-11-01

The anatomical form of a tooth can undergo changes leading to loss of tooth form. The loss of tooth surface can be due to varying etiology. Dental caries, attrition, abrasion, erosion, involving any surface of the tooth can lead to loss of tooth structure. The rate of tooth destruction may proceed to such an extent that the esthetics, function and comfort may be lost. The role of a practioner lies in identification and screening of such case and motivate for oral rehabilitation that includes habit cessation. Computerized dentistry has raised the bar as far as esthetic restorations are concerned. Demanding esthetics has made zirconia crowns as the material of choice in full mouth rehabilitations. However, appropriate treatment planning with scientific evidence and a recommended treatment protocol with careful implementation results in successful restorations and satisfied patients.