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Biomedical subjects

N Spencer

Publications and source records attributed to N Spencer.

At least 19 recordsLinked to original sources
PubMed2002

Nanochemical surface analyzer in CMOS technology.

We have developed an atomic force microscopy (AFM) cantilever system, fabricated using a standard CMOS process and a few post-processing steps, capable of detecting the difference between hydrophilic and hydrophobic samples for the purpose of nanochemical surface analysis. The fully integrated cantilever comprises a thermal actuator for cantilever deflection and a Wheatstone bridge to sense cantilever bending, thus obviating the need for cumbersome laser detection and external piezoelectric drives. Glass microspheres have been affixed to the cantilevers and, were either modified with a self-assembled monolayer to form hydrophobic tips, or left unmodified for hydrophilic tips. Force-distance curves have been used to measure the force between the functionalized/unfunctionalized tips and hydrophobic/hydrophilic sample surfaces. In an optimization step three different Wheatstone bridge sensors have been designed and characterized; best Wheatstone bridge sensitivity is 8.0 microV/nm with a 713 nm/mW actuator efficiency.

Journal Article↗
PubMed2002

Growth of working boys in Jordan: a cross-sectional survey using non-working male siblings as comparisons.

OBJECTIVES: To study the effects of work on growth of Jordanian boys, aged 10-16 years, using non-working male siblings as controls. SETTING: The Jordanian areas of Irbid, Jarash and the North Jordan Valley. STUDY DESIGN: Cross-sectional survey of working boys and their non-working brothers. MAIN OUTCOMES: Height-for-age z-score; weight-for-age z-score. METHODS: Working boys (103) and non-working male siblings (103) (nearest in age to the working child) were interviewed, with their mothers, in the family home. Heights and weights of the working boys and their non-working male siblings were measured, and capillary blood was taken for packed-cell volume estimation. Heights and weights were converted to z-scores, and means for all three outcomes were compared between working boys and non-working siblings, using independent sample t-tests. The effect of the proportion of household income contributed by the working child's income on the main outcomes, among non-working siblings, was estimated by simple linear regression. RESULTS: Means for height-for-age z-score (p < 0.001), weight-for-age z-score (p < 0.001), and packed-cell volume (p < 0.001) among working boys were significantly lower than means for their non-working siblings. The main outcomes among non-working siblings were not significantly correlated with the proportion of household income contributed by the working child. CONCLUSIONS: The results of this study suggest that work among boys aged 10-16 years in Jordan puts them at increased risk of stunting, wasting and anaemia. Previous studies have suggested this relationship but have suffered from confounding by socioeconomic status. Comparison with non-working siblings reduces the chances of socioeconomic status confounding.

Adolescent↗
PubMed2001

Transfer of stereochemical information in a minimal self-replicating system.

[structure: see text]. The rational design, synthesis, and characterization of a minimal self-replicating system based on a 1,3-dipolar cycloaddition between a nitrone and a maleimide is presented. The importance of molecular recognition in this system is demonstrated using a competitive inhibitor. Doping experiments demonstrate that only one of the two diastereoisomeric products of the cycloaddition reaction is capable of acting as an efficient template for its own formation, accelerating the reaction between the nitrone and maleimide and controlling the stereochemical outcome of the reaction.

Journal Article↗
PubMed2001

Work, family socioeconomic status, and growth among working boys in Jordan.

AIMS: To describe the work, family socioeconomic characteristics, and growth of a representative sample of working children in Jordan. METHODS: In a cross sectional survey of growth and health, 135 working children (aged 10-16 years) were studied in the areas of Irbid, Jarash, and North Jordan Valley. The children and their parents were interviewed and data collected on length of working week, income earned by the child, duration of work in years, age of starting work, type of work, child's smoking status, and family socioeconomic status. RESULTS: The mean age of the children was 13.3 years; 14.8% had started work before the age of 10 and 12.6% had been working for more than four years. Mean income was 34 Jordanian Dinars but 6.7% were unwaged; 34% were working more than 60 hours per week, and 85.9% more than 40 hours. Monthly income and working hours were positively correlated with the age of the child. There was no correlation between age and smoking status; 37.8% smoked more than five cigarettes per day. Mean height and weight z scores were -0.365 and -0.081 of the UK standard respectively. Packed cell volume was within the anaemic range in 34.1% of children. CONCLUSIONS: In Jordan many children start work at an early age and work long hours for little or no income. Stunting and anaemia are common and many are established smokers. Relevance of these findings for social policy and health care of working children in Jordan and elsewhere is discussed.

Adolescent↗
PubMed2000

A photochemically driven molecular-level abacus

A molecular-level abacus-like system driven by light inputs has been designed in the form of a [2]rotaxane, comprising the pi-electron-donating macrocyclic polyether bis-p-phenylene-34-crown-10 (BPP34C10) and a dumbbell-shaped component that contains 1) a Ru(II) polypyridine complex as one of its stoppers in the form of a photoactive unit, 2) a p-terphenyl-type ring system as a rigid spacer, 3) a 4,4'-bipyridinium unit and a 3,3'-dimethyl-4,4'-bipyridinium unit as pi-electron-accepting stations, and 4) a tetraarylmethane group as the second stopper. The synthesis of the [2]rotaxane was accomplished in four successive stages. First of all, the dumbbell-shaped component of the [2]rotaxane was constructed by using conventional synthetic methodology to make 1) the so-called "west-side" comprised of the Ru(II) polypyridine complex linked by a bismethylene spacer to the p-terphenyl-type ring system terminated by a benzylic bromomethyl function and 2) the so-called "east-side" comprised of the tetraarylmethane group, attached by a polyether linkage to the bipyridinium unit, itself joined in turn by a trismethylene spacer to an incipient 3,3'-dimethyl-4,4'-bipyridinium unit. Next, 3) the "west-side" and "east-side" were fused together by means of an alkylation to give the dumbbell-shaped compound, which was 4) finally subjected to a thermodynamically driven slippage reaction, with BPP34C10 as the ring, to afford the [2]rotaxane. The structure of this interlocked molecular compound was characterized by mass spectrometry and NMR spectroscopy, which also established, along with cyclic voltammetry, the co-conformational behavior of the molecular shuttle. The stable translational isomer is the one in which the BPP34C10 component encircles the 4,4'-bipyridinium unit, in keeping with the fact that this station is a better pi-electron acceptor than the other station. This observation raises the question- can the BPP34C10 macrocycle be made to shuttle between the two stations by a sequence of photoinduced electron transfer processes? In order to find an answer to this question, the electrochemical, photophysical, and photochemical (under continuous and pulsed excitation) properties of the [2]rotaxane, its dumbbell-shaped component, and some model compounds containing electro- and photoactive units have been investigated. In an attempt to obtain the photoinduced abacus-like movement of the BPP34C10 macrocycle between the two stations, two strategies have been employed-one was based fully on processes that involved only the rotaxane components (intramolecular mechanism), while the other one required the help of external reactants (sacrificial mechanism). Both mechanisms imply a sequence of four steps (destabilization of the stable translational isomer, macrocyclic ring displacement, electronic reset, and nuclear reset) that have to compete with energy-wasteful steps. The results have demonstrated that photochemically driven switching can be performed successfully by the sacrificial mechanism, whereas, in the case of the intramolecular mechanism, it would appear that the electronic reset of the system is faster than the ring displacement.

Journal Article↗
PubMed2000

Is bowel preparation useful before radiography of the renal tract in patients with spinal cord injury?

OBJECTIVES: To assess, in a blinded study, the usefulness of bowel preparation in improving the quality of radiography of the renal tract in patients with spinal cord injury (SCI). PATIENTS AND METHODS: Plain abdominal radiographs of 56 patients with SCI were selected; 24 of the patients had received bowel preparation and 32 had not. The films were independently assessed by one radiologist and one urologist unaware of the treatment and identity of the patients. Each film was divided into five regions of interest and scores of 1-4 (1 for least and 4 for best visibility) assigned to each area. In films with a low aggregate visibility score (</= 12), the cause of poor visibility was assessed in relation to faecal residue and gas. RESULTS: The difference between the overall mean visibility score for bowel-prepared and unprepared patients was not statistically significant. In films with poor visibility, gas shadows predominated over bowel shadows in the bowel-prepared group, although this trend was not statistically significant. Of the five areas, the bladder was scored as being the most clearly seen in both groups. CONCLUSIONS: These findings suggest that bowel preparation does not increase the diagnostic value of radiographs of the renal tract in patients with SCI.

Cathartics↗
PubMed2000

Are Armed Forces infants more at risk than civilian infants?

The aim of the present study is to compare the health status of Armed Forces and civilian infants, accounting for social class. In a prospective cohort study, demographic data were obtained from mothers of liveborn infants from 436 civilian and 162 Armed Forces families. Birth details were taken from hospital maternity and child health systems. A six month follow-up was completed by health visitors. Standard social class classification, based on occupation, was used for civilian families and a new equivalent scheme for military personnel. No significant differences were found between civilian and military infants for birthweight, prematurity and failure to thrive. Military infants had significantly more hospital admissions (P=0.015) and accident and emergency attendances (P=0.002) mainly accounted for by the 'manual' social classes of the Armed Forces. Infant health status of civilian and military babies did not differ overall. Increased uptake of hospital services by military families can be explained by local circumstances.

Adult↗
PubMed1999

Sympathetic inhibition of ascending and descending interneurones during the peristaltic reflex in the isolated guinea-pig distal colon.

1. We investigated the effects of sympathetic nerve stimulation within ascending and descending reflex pathways underlying the peristaltic reflex in the guinea-pig distal colon. 2. A three-chambered partitioned bath was used to divide a segment of distal colon into stimulation, recording and intermediate regions. The effects of lumbar colonic nerves (LCN) could be localized to the intermediate region by surgical lesions of the mesentery and by application of guanethidine (3 microM) to the stimulation and recording chambers. 3. Brush stroking the mucosa in the anal and oral stimulation chambers elicited a synchronous contraction of the longitudinal muscle (LM) and circular muscle (CM) oral to, and transient relaxation of the LM and CM anal to, the stimulus, respectively. 4. After N omega-nitro-L-arginine (L-NA; 100 microM) in the oral and intermediate chambers, mucosal stimulation in the oral chamber elicited a prolonged descending inhibitory and excitatory complex in both the LM and CM in the anal recording chamber. This was blocked by hexamethonium (300 microM), which did not affect the transient relaxation response recorded in control conditions. 5. Stimulation of the LCN (1200 pulses, 20 Hz), delivered to the intermediate region, abolished the oral contraction and the L-NA-induced anal complex in both the LM and CM, but was without effect on the transient hexamethonium-resistant anal relaxation. These effects of LCN stimulation were reversed by phentolamine (3 microM) or yohimbine (100 nM), but not propranolol (10 microM), when added to the intermediate chamber. 6. LCN stimuli (2-20 Hz, 600 micros pulses) directed to the recording chamber elicited synchronous relaxations in the LM and CM that were unaffected by hexamethonium (300 microM), but were reduced by yohimbine and usually blocked by the further addition of propranolol (10 microM). 7. In conclusion, sympathetic nerve stimulation inhibits orally and anally projecting cholinergic interneurones underlying the peristaltic reflex in the distal colon. In addition, the LM and CM relax synchronously following release of sympathetic neurotransmitter, over a range of stimulus frequencies.

Adrenergic alpha-Agonists↗