PubMed Health⌕ Search

Biomedical subjects

M Lord

Publications and source records attributed to M Lord.

At least 19 recordsLinked to original sources
PubMed2002

On-line measurement of texture, thickness and plastic strain ratio using laser-ultrasound resonance spectroscopy.

Laser-ultrasound resonance spectroscopy, a non-contact ultrasonic technique, was used to determine reliably and rapidly the crystallographic texture, the average plastic strain ratio, and the thickness of sheet metal on the production line. As with laser-ultrasonics, a short laser pulse is used to generate a wide-band pulse of ultrasound and a laser interferometer is used for its detection. In this paper, a large number of echoes are collected and analyzed together using Fourier techniques to measure the natural resonance frequencies in the thickness of the sheet. One longitudinal and two shear resonance frequencies were measured together with their harmonics. From these frequencies, two crystallographic orientation distribution coefficients, W(400) and W(420), are obtained, as well as a highly accurate measurement of the sheet thickness that is corrected for changes in ultrasonic velocity caused by texture variations. Using these coefficients, the average and in-plane twofold and fourfold variations of the plastic strain ratio, respectively r delta(2)r, and delta(4)r, can be evaluated. These parameters are indications of the formability of metals sheets, which is of industrial interest. Measurements on 1 mm thick, low carbon steel sheets have shown the following measurement accuracies: r to within +/-0.08, delta(2)r, and delta(4)r to within +/-0.1, and thickness to better than +/-1 microm. On-line tests at LTV Steel Company showed that the sensitivity of the apparatus is sufficient to detect systematic variations in texture along the length of similar production coils and that the on-line repeatability for r was of order +/-0.02.

Journal Article↗
PubMed2001

NMR studies of the sporulation protein SpoIIAA: implications for the regulation of the transcription factor sigmaF in Bacillus subtilis.

SpoIIAA participates in a four-component mechanism for phosphorylation-dependent transcription control at the outset of sporulation. We report the refinement of the solution structure of SpoIIAA by using the automated iterative NOE assignment method ARIA. To complement the structural data, the protein dynamics were determined by measuring the T1, T2 and NOE of the backbone 15N-nuclei. The refined structure permits a discussion of the structural features that are important for the function of SpoIIAA in the regulation of the sporulation sigma factor sigmaF, and for homologous regulatory pathways present in B. subtilis and in other bacilli.

Bacillus subtilis↗
PubMed2000

Cell cycle programs of gene expression control morphogenetic protein localization.

Genomic studies in yeast have revealed that one eighth of genes are cell cycle regulated in their expression. Almost without exception, the significance of cell cycle periodic gene expression has not been tested. Given that many such genes are critical to cellular morphogenesis, we wanted to examine the importance of periodic gene expression to this process. The expression profiles of two genes required for the axial pattern of cell division, BUD3 and BUD10/AXL2/SRO4, are strongly cell cycle regulated. BUD3 is expressed close to the onset of mitosis. BUD10 is expressed in late G1. Through promotor-swap experiments, the expression profile of each gene was altered and the consequences examined. We found that an S/G2 pulse of BUD3 expression controls the timing of Bud3p localization, but that this timing is not critical to Bud3p function. In contrast, a G1 pulse of BUD10 expression plays a direct role in Bud10p localization and function. Bud10p, a membrane protein, relies on the polarized secretory machinery specific to G1 to be delivered to its proper location. Such a secretion-based targeting mechanism for membrane proteins provides cells with flexibility in remodeling their architecture or evolving new forms.

Cell Cycle↗
PubMed2000

Multigenerational cortical inheritance of the Rax2 protein in orienting polarity and division in yeast.

Diploid yeast cells repeatedly polarize and bud from their poles, probably because of highly stable marks of unknown composition. Here, Rax2, a membrane protein, was shown to behave as such a mark. The Rax2 protein itself was inherited immutably at the cell cortex for multiple generations, and Rax2 was shown to have a half-life exceeding several generations. The persistent inheritance of cortical protein markers would provide a means to couple a cell's history to the future development of a precise morphogenetic form.

Cell Division↗
PubMed2000

A study of in-shoe plantar shear in normals.

OBJECTIVE: To quantify features of in-shoe plantar shear in asymptomatic adult gait. DESIGN: In order to standardize footwear conditions and facilitate later comparison to patient groups, measurement is made in a group of adults walking freely in stock orthopaedic footwear. BACKGROUND: Better data on plantar shear is required to complement well-documented pressure data for an overall picture of plantar stress. METHODS: Measurements were made locally beneath the medial four metatarsal heads and heel using biaxial transducers mounted flush into an inlay. Pressure distribution was also measured. RESULTS: The shear data revealed common features in the shear pattern occurring at defined phases of gait, with good inter-step reliability. For the five sites of interest, these values ranged from 24 kPa to 70.4 kPa, and 31 kPa to 86.5 kPa for individuals wearing nylon hose or hose-free respectively. Maximum shear occurred more laterally than maximum pressure. CONCLUSIONS: Features of plantar shear were not always as expected; for example the forward thrust at push-off was not reflected in the anteroposterior shear stress. Because of the inter-subject variability, study of a larger group is indicated. RELEVANCE: Mechanical stress at the plantar interface between foot and shoe is of particular clinical relevance to the formation and management of ulcers in diabetic neuropathy. It is also of relevance to shoe and orthotic design for various foot pathologies. This study provides reliable data on the shear component of plantar stress for which, unlike the well-documented pressure component, there is only sparse data so far available.

Adult↗
PubMed2000

A study of in-shoe plantar shear in patients with diabetic neuropathy.

OBJECTIVE: To quantify in-shoe plantar shear in diabetic neuropathic feet. DESIGN: Plantar shear stresses are measured in a group of six patients with a history of diabetic neuropathic ulceration. BACKGROUND: Although elevated pressure between foot and shoe frequently found in diabetic neuropathic patients has been linked to a raised incidence of plantar ulceration, the shear component of stress at this interface is as yet unquantified. It is suggested that its effects may be equally damaging. METHODS: Measurements of shear were made locally beneath the medial four metatarsal heads and heel during unpaced gait in orthopaedic footwear, using a bi-axial magneto-resistive shear transducer. Similar methodology was previously employed on a group of asymptomatic adults, thereby allowing comparisons to be made. RESULTS: Overall the maximum shear stress for this patient group (73 kPa) was not significantly different to that in the asymptomatic group (87 kPa). However the patient group exhibited lower magnitudes of shear stress under the third/fourth metatarsal heads (average 51/39 vs. 86.5/71 kPa, respectively) and higher magnitudes under the first/second heads (73/64 vs. 35/31 kPa, respectively), indicating a medial shift. Step-to-step variability of maximum shear measured under the third metatarsal head showed an increase in the transverse component (coefficient of reliability 67% vs. 98%). CONCLUSIONS: Although the overall patterns of shear are broadly similar to the asymptomatic group, these pilot trials indicate a medial shift in shear loading under the forefoot coupled to increased step-to-step variability in the diabetic group. RelevanceMechanical stress at the plantar interface between foot and shoe is of particular clinical relevance to the formation and management of ulcers in diabetic neuropathy. Whereas the pressure component of stress is widely studied, the shear component is poorly described although it may be of equal importance.

Aged↗
PubMed1999

Replacement of vegetative sigmaA by sporulation-specific sigmaF as a component of the RNA polymerase holoenzyme in sporulating Bacillus subtilis.

Soon after asymmetric septation in sporulating Bacillus subtilis cells, sigmaF is liberated in the prespore from inhibition by SpoIIAB. To initiate transcription from its cognate promoters, sigmaF must compete with sigmaA, the housekeeping sigma factor in the predivisional cell, for binding to core RNA polymerase (E). To estimate the relative affinity of E for sigmaA and sigmaF, we made separate mixtures of E with each of the two sigma factors, allowed reconstitution of the holoenzyme, and measured the concentration of free E remaining in each mixture. The affinity of E for sigmaF was found to be about 25-fold lower than that for sigmaA. We used quantitative Western blotting to estimate the concentrations of E, sigmaA, and sigmaF in sporulating cells. The cellular concentrations of E and sigmaA were both about 7.5 microM, and neither changed significantly during the first 3 h of sporulation. The concentration of sigmaF was extremely low at the beginning of sporulation, but it rose rapidly to a peak after about 2 h. At its peak, the concentration of sigmaF was some twofold higher than that of sigmaA. This difference in concentration cannot adequately account for the replacement of sigmaA holoenzyme by sigmaF holoenzyme in the prespore, and it seems that some further mechanism-perhaps the synthesis or activation of an anti-sigmaA factor-must be responsible for this replacement.

Bacillus subtilis↗
PubMed1999

Plantar pressures are elevated in the neuroischemic and the neuropathic diabetic foot.

OBJECTIVE: Clinical observation has noted that diabetic neuropathic ulcers occur frequently on the plantar surface, whereas neuroischemic ulcers seem to occur often on the foot margins. The reason for this difference in the site of ulceration is unknown, but it may be related to differences in pressure loading. The aim of the study was to compare vertical in-shoe foot pressures measured during walking (using the F-SCAN system) in four groups of patients whose degree of neuropathy was measured by vibration perception threshold (VPT). RESEARCH DESIGN AND METHODS: Subjects included 14 neuroischemic diabetic patients (VPT 29.3 +/- 13.5 V) with history of ulceration on the margins of the foot, 18 patients with neuropathy alone (VPT 38.7 +/- 12.7 V) and previous history of ulceration on the plantar surface, 10 diabetic control patients (VPT 9.9 +/- 2.7 V), and 15 nondiabetic control subjects (VPT 7.0 +/- 0.5 V). RESULTS: When compared with the other three groups, neuroischemic patients had higher foot pressures when measured as mean peak pressures and highest peak pressures under four areas of the foot: medial and lateral forefoot, hallux, and heel. Furthermore, when measuring the maximum pressures developed at any point under the plantar surface, the neuroischemic patients also had the most elevated pressures (757.6 +/- 135.9 kPa), significantly higher than those found in the neuropathic group (482.8 +/- 68.6 kPa, P = 0.04) and in both diabetic control patients (310.2 +/- 34.7 kPa, P = 0.008) and nondiabetic controls subjects (365.1 +/- 49.8 kPa, P = 0.007). CONCLUSIONS: Despite having increased plantar pressures and a comparable degree of neuropatny, the neuroischemic patients did not have a history of ulceration on the plantar surface. These observations may have relevance to different mechanisms of ulcer formation in the neuroischemic and neuropathic foot.

Diabetic Angiopathies↗