Stiffness prediction for bolted moment-connections between cold-formed steel members

The authors have recently described a cold-formed steel portal framing system in which simple bolted moment-connections, formed through brackets, were used for the eaves and apex joints. Such connections, however, cannot be considered as rigid because of localised in-plane elongation of the bolt-holes caused by bearing against the bolt-shanks. To therefore predict the initial stiffness of such connections, it is necessary to know the initial bolt-hole elongation stiffness k(b). In this paper, a finite element-solid idealisation of a bolted lap joint in shear will be described that can be used to determine k(b); the results obtained are validated against experimental data. A beam idealisation of a cold-formed steel bolted moment-connection is then described, in which spring elements are used to idealise the rotational flexibility of the bolt-groups resulting from bolt-hole elongation: Using the value of k(b) in the beam idealisation, the deflections predicted are shown to be similar to those measured experimentally in laboratory tests conducted on the apex joint of a cold-formed steel portal frame. (C) 2003 Elsevier Ltd. All rights reserved.

The electrical characterization and response to hydrogen of Schottky diodes with a resistive metal electrode—rectifying an oversight in Schottky diode investigation

Schottky-barrier structures with a resistive metal electrode are examined using the 4-point probe method where the probes are connected to the metal electrode only. The observation of a significant decrease in resistance with increasing temperature (over a range of similar to 100 K) in the diode resistance-temperature (R(D)-T) characteristic is considered due to charge carrier confinement to the metal electrode at low temperature (high resistance), with the semiconductor progressively opening up as a parallel current carrying channel (low resistance) with increasing temperature due to increasing thermionic emission across the barrier. A simple model is constructed, based on thermionic emission at quasi-zero bias, that generates good fits to the experimental data. The negative differential resistance (NDR) region in the R(D)-T characteristic is a general effect and is demonstrated across a broad temperature range for a variety of Schottky structures grown on Si-, GaAs- and InP-substrates. In addition the NDR effect is harnessed in micro-scaled Pd/n-InP devices for the detection of low levels of hydrogen in an ambient atmosphere of nitrogen.

The Behavior of compressively loaded stiffener runout specimens - Part II: Finite element analysis

The termination of stiffeners in composite aircraft structures give rise to regions of high interlaminar shear and peel stresses as the load in the stiffener is diffused into the skin. This is of particular concern in co-cured composite stiffened structures where there is a relatively low resistance to through-thickness stress components at the skin-stiffener interface. In Part I, experimental results of tested specimens highlighted the influence of local design parameters on their structural response. Indeed some of the observed behavior was unexpected. There is a need to be able to analyse a range of changes in geometry rapidly to allow the analysis to form an integral part of the structural design process.

This work presents the development of a finite element methodology for modelling the failure process of these critical regions. An efficient thick shell element formulation is presented and this element is used in conjuction with the Virtual Crack Closure Technique (VCCT) to predict the crack growth characteristics of the modelled specimens. Three specimens were modelled and the qualitative aspects of crack growth were captured successfully. The shortcomings in the quantitative correlation between the predicted and observed failure loads are discussed. There was evidence to suggest that high through-thickness compressive stresses enhanced the fracture toughness in these critical regions.

Modelling and visualisation of material flow in friction stir spot welding

Abstract The material flow in friction stir spot welding of aluminium to both aluminium and steel has been investigated, using pinless tools in a lap joint geometry. The flow behaviour was revealed experimentally using dissimilar Al alloys of similar strength. The effect on the material flow of tool surface features, welding conditions (rotation speed, plunge depth, dwell time), and the surface state of the steel sheet (un-coated or galvanized) have been systematically studied. A novel kinematic flow model is presented, which successfully predicts the observed layering of the dissimilar Al alloys under a range of conditions. The model and the experimental observations provide a consistent interpretation of the stick-slip conditions at the tool-workpiece interface, addressing an elusive and long-standing issue in the modelling of heat generation in friction stir processing.

Effect of eucaloric high- and low-sucrose diets with identical macronutrient profile on insulin resistance and vascular risk - A randomized controlled trial

The long-term impact of dietary carbohydrate type, in particular sucrose, on insulin resistance and the development of diabetes and atherosclerosis is not established. Current guidelines for the healthy population advise restriction of sucrose intake. We investigated the effect of high- versus low-sucrose diet (25 vs. 10%, respectively, of total energy intake) in 13 healthy subjects aged 33 +/- 3 years (mean +/- SE), BMI 26.6 +/- 0.9 kg/m(2), in a randomized crossover design with sequential 6-week dietary interventions separated by a 4-week washout. Weight maintenance, eucaloric diets with identical macronutrient profiles and fiber content were designed. All food was weighed and distributed. Insulin action was assessed using a two-step euglycemic clamp; glycemic profiles were assessed by the continuous glucose monitoring system and vascular compliance by pulse-wave analysis. There was no change in weight across the study. Peripheral glucose uptake and suppression of endogenous glucose production were similar after each diet. Glycemic profiles and measures of vascular compliance did not change. A rise in total and LDL cholesterol was observed. In this study, a high-sucrose intake as part of an eucaloric, weight-maintaining diet had no detrimental effect on insulin sensitivity, glycemic profiles, or measures of vascular compliance in healthy nondiabetic subjects.

Mutations affecting the Rossman fold of isoleucyl-tRNA synthetase are correlated with low-level mupirocin resistance in Staphylococcus aureus.

The isoleucyl-tRNA synthetase (ileS) gene was sequenced in toto from 9 and in part from 31 Staphylococcus aureus strains with various degrees of susceptibility to mupirocin. All strains for which the mupirocin MIC was greater than 8 µg/ml contained point mutations affecting the Rossman fold via Val-to-Phe changes at either residue 588 (V588F) or residue 631 (V631F). The importance of the V588F mutation was confirmed by an allele-specific PCR survey of 32 additional strains. Additional mutations of uncertain significance were found in residues clustered on the surface of the IleS protein.

Transfer of resistance training to enhance rapid coordinated force production by older adults

The purpose of this study was to examine the capacity of resistance training to enhance the rapid and coordinated production of force by older people. Thirty adults (greater than or equal to 60 years) completed a visually guided aiming task that required the generation of isometric torque in 2 df about the elbow prior to and following a 4-week training period. Groups of six participants were allocated to two progressive ( 40 - 100% maximal voluntary contraction (MVC)) resistance-training (PRT) groups, to two constant low-load (10% MVC) training groups (CLO) and to one no-training control group. Training movements required the generation of either combined flexion and supination (FLESUP), or combined extension and supination (EXTSUP). In response to training, target acquisition times in the aiming task decreased for all groups; however, both the nature of the training load and the training movement influenced the pattern and magnitude of improvements (EXTSUP_ CLO: 36%, FLESUP_ PRT 26%, EXTSUP_ PRT 22%, FLESUP_ CLO 20%, CONTROL 15%). For one group that trained with progressively increasing loads, there arose a subsequent decrease in performance in one condition of the transfer task. For each group, these adaptations were accompanied by systematic changes in the coordination of muscles about the elbow joint, particularly the biceps brachii.

Low-energy electron attachment to chloroform (CHCl3) molecules: A joint experimental and theoretical study

Results from a joint experimental and theoretical study of electron attachment to chloroform (CHCl3) molecules in the gas phase are reported. In an electron swarm study involving a pulsed Townsend technique with equal gas and electron temperatures, accurate attachment rate coefficients were determined over the temperature range 295-373 K; they show an Arrhenius-type rise with increasing temperature, corresponding to an activation energy of 0.11 (1) eV. In a high resolution electron beam experiment involving two versions of the laser photoelectron attachment method, the relative cross section for Cl- formation from CHCl3 over the energy range 0.001-1.25 eV at the gas temperature T-G = 300 K was measured. It exhibits clear downward cusp structure at the threshold for excitation of one quantum of the vibrational symmetric deformation mode nu(3), indicating that this mode is active in the primary attachment process. With reference to our thermal attachment rate coefficient k(T = 300 K) = 3.9(2) x 10(-9) cm(3) s(-1), a new highly resolved absolute attachment cross section for T-G = 300 K was determined. This cross section is extended to higher energies by measurements, carried out with a pulsed electron beam apparatus which also provided new data for the distinctly weaker fragment anions HCl2- and CCl2-. The resulting total absolute cross section for anion formation is used to calculate the dependence of the attachment rate coefficient k(T-e;T-G) on electron temperature T-e over the range 50-15000 K at the fixed gas temperature T-G = 300 K. In addition, we report the dependence of the relative cross section for Cl- formation on gas temperature T-G = 310-435 K). For comparison with the experimental data, R-matrix calculations have been carried out for the dominant anion channel Cl-. The results recover the main experimental observations and predict the dependence of the DEA cross section on the initial vibrational level nu(3) and on the vibrational temperature. Our results are compared with those of previous electron beam and electron swarm experiments.

Low-fat versus low-carbohydrate weight reduction diets:Effects on weight loss, insulin resistance, and cardiovascular risk: a randomized control trial

OBJECTIVE Low-fat hypocaloric diets reduce insulin resistance and prevent type 2 diabetes in those at risk. Low-carbohydrate, high-fat diets are advocated as an alternative, but reciprocal increases in dietary fat may have detrimental effects on insulin resistance and offset the benefits of weight reduction.

RESEARCH DESIGN AND METHODS We investigated a low-fat (20% fat, 60% carbohydrate) versus a low-carbohydrate (60% fat, 20% carbohydrate) weight reduction diet in 24 overweight/obese subjects ([mean ± SD] BMI 33.6 ± 3.7 kg/m2, aged 39 ± 10 years) in an 8-week randomized controlled trial. All food was weighed and distributed, and intake was calculated to produce a 500 kcal/day energy deficit. Insulin action was assessed by the euglycemic clamp and insulin secretion by meal tolerance test. Body composition, adipokine levels, and vascular compliance by pulse-wave analysis were also measured.

RESULTS Significant weight loss occurred in both groups (P < 0.01), with no difference between groups (P = 0.40). Peripheral glucose uptake increased, but there was no difference between groups (P = 0.28), and suppression of endogenous glucose production was also similar between groups. Meal tolerance–related insulin secretion decreased with weight loss with no difference between groups (P = 0.71). The change in overall systemic arterial stiffness was, however, significantly different between diets (P = 0.04); this reflected a significant decrease in augmentation index following the low-fat diet, compared with a nonsignificant increase within the low-carbohydrate group.

CONCLUSIONS This study demonstrates comparable effects on insulin resistance of low-fat and low-carbohydrate diets independent of macronutrient content. The difference in augmentation index may imply a negative effect of low-carbohydrate diets on vascular risk.

Low cytosine triphosphate synthase 2 expression renders resistance to 5-fluorouracil in colorectal cancer

Understanding the determinants of resistance of 5-fluorouracil (5FU) is of significant value to optimizing administration of the drug, and introducing novel agents and treatment strategies. Here, the expression of 92 genes involved in 5FU transport, metabolism, co-factor (folate) metabolism and downstream effects was measured by real-time PCR low density arrays in 14 patient-derived colorectal cancer xenografts characterized for 5FU resistance. Candidate gene function was tested by siRNA and uridine modulation, and immunoblotting, apoptosis and cell cycle analysis. Predictive significance was tested by immunohistochemistry of tumors from 125 stage III colorectal cancer patients treated with and without 5FU. Of 8 genes significantly differentially expressed between 5FU sensitive and resistant xenograft tumors, CTPS2 was the gene with the highest probability of differential expression (p = 0.008). Reduction of CTPS2 expression by siRNA increased the resistance of colorectal cancer cell lines DLD1 and LS174T to 5FU and its analog, FUDR. CTPS2 siRNA significantly reduced cell S-phase accumulation and apoptosis following 5FU treatment. Exposure of cells to uridine, a precursor to the CTPS2 substrate uridine triphosphate, also increased 5FU resistance. Patients with low CTPS2 did not gain a survival benefit from 5FU treatment (p = 0.072), while those with high expression did (p = 0.003). Low CTPS2 expression may be a rationally-based determinant of 5FU resistance.

Hopanoid Production Is Required for Low-pH Tolerance, Antimicrobial Resistance, and Motility in Burkholderia cenocepacia

Hopanoids are pentacyclic triterpenoids that are thought to be bacterial surrogates for eukaryotic sterols, such as cholesterol, acting to stabilize membranes and to regulate their fluidity and permeability. To date, very few studies have evaluated the role of hopanoids in bacterial physiology. The synthesis of hopanoids depends on the enzyme squalene-hopene cyclase (Shc), which converts the linear squalene into the basic hopene structure. Deletion of the 2 genes encoding Shc enzymes in Burkholderia cenocepacia K56-2, BCAM2831 and BCAS0167, resulted in a strain that was unable to produce hopanoids, as demonstrated by gas chromatography and mass spectrometry. Complementation of the Delta shc mutant with only BCAM2831 was sufficient to restore hopanoid production to wild-type levels, while introducing a copy of BCAS0167 alone into the Delta shc mutant produced only very small amounts of the hopanoid peak. The Delta shc mutant grew as well as the wild type in medium buffered to pH 7 and demonstrated no defect in its ability to survive and replicate within macrophages, despite transmission electron microscopy (TEM) revealing defects in the organization of the cell envelope. The Delta shc mutant displayed increased sensitivity to low pH, detergent, and various antibiotics, including polymyxin B and erythromycin. Loss of hopanoid production also resulted in severe defects in both swimming and swarming motility. This suggests that hopanoid production plays an important role in the physiology of B. cenocepacia.

Antioxidants, but not B-group vitamins increase the resistance of low-density lipoprotein to oxidation:a randomized, factorial design, placebo-controlled trial

We have conducted an intervention trial to assess the effects of antioxidants and B-group vitamins on the susceptibility of low-density lipoprotein (LDL) to oxidation. A total of 509 men aged 30-49 from a local workforce were screened for total plasma homocysteine. The 132 selected (homocysteine concentration > or = 8.34 mumol/l) men were randomly assigned, using a factorial design, to one of four groups receiving supplementation with B group vitamins alone (1 mg folic acid, 7.2 mg pyridoxine, 0.02 mg cyanocobalamin), antioxidant vitamins (150 mg ascorbic acid, 67 mg alpha-tocopherol, 9 mg beta-carotene), B vitamins with antioxidant vitamins, or placebo. Intervention was double-blind. A total of 101 men completed the 8-week study. The lag time of LDL isolated ex vivo to oxidation (induced by 2 mumol/l cupric chloride) was increased in the two groups receiving antioxidants whether with (6.88 +/- 1.65 min) or without (8.51 +/- 1.77 min) B-vitamins, compared with placebo (-2.03 +/- 1.50) or B-vitamins alone (-3.34 +/- 1.08) (Mean +/- S.E., P <0.001). Antibodies to malondialdehyde (MDA) modified LDL were also measured, but there were no significant changes in titers of these antibodies in any group of subjects whether receiving antioxidants or not. Contrast analysis showed that there was no interaction between antioxidants and B-group vitamins. This study indicates that while B-group vitamins lower plasma homocysteine they do not have an antioxidant effect. Thus B-group vitamins and antioxidants appear to have separate, independent effects in reducing cardiovascular risk.

Low clusterin levels in high-density lipoprotein associate with insulin resistance, obesity, and dyslipoproteinemia

To determine whether obesity and insulin resistance associate with changes in the protein content of high-density lipoprotein (HDL) in 2 different groups of men by using targeted proteomics.