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Biomedical subjects

M Hanson

Publications and source records attributed to M Hanson.

At least 19 recordsLinked to original sources
PubMed2006

Multipeak Kondo effect in one- and two-electron quantum dots.

We have fabricated a few-electron quantum dot that can be tuned down to zero electrons while maintaining strong coupling to the leads. Using a nearby quantum point contact as a charge sensor, we can determine the absolute number of electrons in the quantum dot. We find several sharp peaks in the differential conductance, occurring at both zero and finite source-drain bias, for the one- and two-electron quantum dot. We attribute the peaks at finite bias to a Kondo effect through excited states of the quantum dot and investigate the magnetic field dependence of these Kondo resonances.

Journal Article↗
PubMed2006

Longitudinal reference ranges for ductus venosus flow velocities and waveform indices.

OBJECTIVES: Serial Doppler measurements of the ductus venosus are used increasingly for monitoring fetuses at risk of hemodynamic compromise, but existing reference ranges are based on cross-sectional studies and thus are less suitable for comparison with serial measurements. We aimed to establish longitudinal reference ranges for ductus venosus flow velocities and waveform indices and to provide the necessary terms for calculating conditional reference ranges for serial measurements. METHODS: This was a longitudinal study of 160 low-risk pregnancies. Pulsed Doppler ultrasound was used to record ductus venosus blood flow velocities at 4-week intervals from 20-22 weeks of gestation onwards. RESULTS: With a success rate of 93%, 547 measurements (four or five in each fetus) were used to establish reference ranges. The time-averaged maximum velocity was 50 cm/s at 21 weeks of gestation, increased to 60 cm/s at 32 weeks, and remained so until term. Similarly, the peak systolic velocity increased from 59 cm/s at 21 weeks to 71 cm/s at 31 weeks and remained so until term. The end-diastolic velocity showed a continuous increase from 31 cm/s at 21 weeks to 43 cm/s at 40 weeks. The pulsatility index for veins decreased from 0.57 at 21 weeks to 0.44 at 40 weeks. When conditioned by a previous measurement, the reference ranges for the next observation became narrower and commonly shifted compared with those of the entire population. CONCLUSION: The new longitudinal reference ranges presented here reflect the development of the ductus venosus flow velocities and velocity indices and are thus appropriate for serial measurements, particularly if conditional terms are included.

Adult↗
PubMed2005

Voiding pattern and acquisition of bladder control from birth to age 6 years--a longitudinal study.

PURPOSE: We describe the voiding pattern and acquisition of bladder control in healthy children up to age 6 years. MATERIALS AND METHODS: We determined age for daytime and nighttime dryness, voiding patterns, voiding volumes and post-void residual volume per 4 hours individually and noninvasively every 3 months up to age 3 years and every 6 months up to age 6 years in 36 female and 23 male patients using 4-hour voiding observation and uroflowmetry/ultrasound. RESULTS: Median age for attaining daytime and nighttime dryness was 3.5 and 4 years, respectively. No significant difference was found between girls and boys. All but 1 child attained daytime dryness an average of 10 months before attaining nighttime dryness. Bladder sensation was reported in 31%, 79% and 100% of patients at ages 2, 3 and 4 years, respectively. Median bladder capacity was 67 ml, 123 ml and 140 ml at years 1, 3 and 6, respectively. Median post-void residual volume was 5.5 ml, 0 ml and 2 ml at ages 1, 3 and 6 years, respectively. CONCLUSIONS: Today bladder control is acquired at a later stage despite earlier awareness of bladder function. The occurrence of bladder sensation from age 1.5 years motivates an earlier start with toilet training. Infants with small post-void residual volume at age 6 months or large bladder capacity will probably attain daytime dryness earlier than those with large post-void residual volume at age 6 months or small bladder capacity.

Age Factors↗
PubMed2004

SNCA multiplication is not a common cause of Parkinson disease or dementia with Lewy bodies.

The authors recently have shown that triplication of the alpha-synuclein gene (SNCA) can cause Parkinson disease (PD) and diffuse Lewy body disease within the same kindred. The authors assessed 101 familial PD probands, 325 sporadic PD cases, 65 patients with dementia with Lewy bodies, and 366 neurologically normal control subjects for SNCA multiplication. The authors did not identify any subjects with multiplication of SNCA and conclude this mutation is a rare cause of disease.

Adult↗
PubMed2004

Portal and umbilical venous blood supply to the liver in the human fetus near term.

OBJECTIVES: To determine the contribution of the umbilical (UV) and portal (PV) veins to blood supply to the human fetal liver in a low-risk population near term, and to assess the distribution between the left and right lobes. METHODS: In 91 low-risk pregnancies with normally grown fetuses at 36 weeks of gestation we measured the distribution of blood in the UV and PV to the right and left hepatic lobes using ultrasound imaging and Doppler techniques. RESULTS: The median (10(th), 90(th) centile) total UV return was 205 (127, 294) mL/min, of which 25% (13, 47%) was shunted through the ductus venosus, 55% (35, 66%) was distributed to the left hepatic lobe, and 20% (11, 30%) was distributed to the right hepatic lobe. While the left lobe was supplied exclusively by the UV, the right lobe received 50% (20, 70%; 37 (16, 65) mL/min) of its venous blood supply from the PV. The total venous blood supply to the liver parenchyma was 185 (114, 277) mL/min; 21% (8, 34%) came from the PV supply to the right lobe and the remainder came from the UV supply to both lobes. CONCLUSIONS: The venous supply to the left lobe is from nutrient-rich UV blood; for the right lobe, half is from UV blood and half from nutrient-poor PV blood. This watershed between the portal and umbilical venous flows to the fetal liver suggests a corresponding functional dichotomy; this may be modified by hemodynamic influences, with long-term consequences.

Adult↗
PubMed2004

Doppler blood flow velocity waveforms in the fetal renal arteries: variability at proximal and distal sites in the right and left arteries.

OBJECTIVE: To investigate variability in pulsatility/resistance indices and absolute velocities of blood flow in fetal renal arteries dependent on side and sampling site within each vessel. METHODS: Doppler blood flow measurements of pulsatility index (PI), resistance index (RI) and peak systolic velocity (PSV) and end-diastolic velocity (EDV) were performed in the renal arteries of 27 fetuses between 236 and 247 days of gestation. Velocity waveforms were sampled in both the right and left renal arteries at two different sites: proximally, close to the aorta, and distally, before any major visible bifurcation of the vessels. The intraobserver variation was measured in 15 additional fetuses. RESULTS: Mean values of PI and RI were similar in the right and left renal arteries and at the proximal and distal sampling sites of these arteries. Mean PSV and EDV were higher at the proximal compared to the distal site on both sides. For all parameters the 95% limits of agreement between measurements made in the right and left arteries and at proximal and distal sites were wide but tended to be narrower for the left renal artery and at the distal site. Intraclass correlation coefficients for intraobserver variability were 0.88, 0.89, 0.83 and 0.81 for PI, RI, PSV and EDV, respectively. CONCLUSIONS: It is important to standardize the precise site at which Doppler blood flow velocity waveform measurements are made in the renal arteries of the fetus. On the basis of our observations, we suggest that the left renal artery is the preferred vessel for sampling and that measurements should be made in the renal arterial trunk away from the aorta and before any visible branches.

Blood Flow Velocity↗
PubMed2003

Spin and polarized current from Coulomb blockaded quantum dots.

We report measurements of spin transitions for GaAs quantum dots in the Coulomb blockade regime and compare ground and excited state transport spectroscopy to direct measurements of the spin polarization of emitted current. Transport spectroscopy reveals both spin-increasing and spin-decreasing transitions, as well as higher-spin ground states, and allows g factors to be measured down to a single electron. The spin of emitted current in the Coulomb blockade regime, measured using spin-sensitive electron focusing, is found to be polarized along the direction of the applied magnetic field regardless of the ground state spin transition.

Journal Article↗
PubMed2003

Evidence for a strong surface-plasmon resonance on ErAs nanoparticles in GaAs.

Room-temperature attenuation measurements are made between lambda=0.8 and 10.0 microm on three GaAs epitaxial samples containing layers of ErAs nanoparticles. An asymmetric attenuation peak is observed around 2.5 microm that increases in strength with ErAs density, and is modeled well by a Maxwell-Garnett formulation and semiclassical transport theory. The nanoparticles are assigned a distribution function of oblate spheroids having a minimum volume corresponding to a 1.0-nm sphere. This is consistent with the self-organizing tendency of ErAs in GaAs, and explains the sharp attenuation peak as a spherical-particle surface-plasmon (i.e., Fröhlich) resonance.

Journal Article↗
PubMed2001

Ferromagnetic imprinting of nuclear spins in semiconductors.

We examine how a ferromagnetic layer affects the coherent electron spin dynamics in a neighboring gallium arsenide semiconductor. Ultrafast optical pump-probe measurements reveal that the spin dynamics are unexpectedly dominated by hyperpolarized nuclear spins that align along the ferromagnet's magnetization. We find evidence that photoexcited carriers acquire spin-polarization from the ferromagnet, and dynamically polarize these nuclear spins. The resulting hyperfine fields are as high as 9000 gauss in small external fields (less than 1000 gauss), enabling ferromagnetic control of local electron spin coherence.

Journal Article↗
PubMed2001

Linkages between facial expressions of anger and transient myocardial ischemia in men with coronary artery disease.

The authors examined whether facial expressions of emotion would predict changes in heart function. One hundred fifteen male patients with coronary artery disease underwent the Type A Structured Interview, during which time measures of transient myocardial ischemia (wall motion abnormality and left ventricular ejection fraction) were obtained. Facial behavior exhibited during the ischemia measurement period was videotaped and later coded by using the Facial Action Coding System (P. Ekman & W. V. Friesen, 1978). Those participants who exhibited ischemia showed significantly more anger expressions and nonenjoyment smiles than nonischemics. Cook-Medley Hostility scores did not vary with ischemic status. The findings have implications for understanding how anger and hostility differentially influence coronary heart disease risk.

Adult↗
PubMed2001

Two rare confounding polymorphisms proximal to the factor V Leiden mutation.

BACKGROUND: Comprehensive assessment of thrombophilia risk includes characterization of the R506Q (Leiden) mutation in factor V in many patients. Although activated protein C resistance is often assessed by means of a coagulation test, molecular interrogation of the G1691A mutation provides confirmation and interpretive utility in patients undergoing anticoagulation. Many molecular methods are available to provide genotyping at this locus. Among these, PCR-restriction fragment length polymorphism (RFLP) is widely used. Unfortunately, because this common mutation is 11 bp from the 3' end of exon 10, one PCR primer often anneals within intron 10. As a consequence, polymorphism can confound test results. METHOD AND RESULTS: In the course of a clinical diagnostic test of 15,301 patients, two samples repeatedly showed two different unusual electrophoretic mobilities after PCR and restriction enzyme digestion. After stripping patient identifiers and entering a research protocol, the amplicons from these DNAs were sequenced in parallel with normal and heterozygous G1691A control genomic DNA samples. This sequencing showed two novel polymorphisms, each mapping to intron 10. CONCLUSION: PCR-RFLP-based methods rely on sequence conservation in the interrogated region. Amplification of mutated loci adjacent to introns present a special risk for confounding restriction patterns. Sequencing amplicons with reproducibly unusual restriction patterns resolved the paradoxical restriction pattern in this case.

Activated Protein C Resistance↗
PubMed2001

Use of a whole genome approach to identify vaccine molecules affording protection against Streptococcus pneumoniae infection.

Microbial targets for protective humoral immunity are typically surface-localized proteins and contain common sequence motifs related to their secretion or surface binding. Exploiting the whole genome sequence of the human bacterial pathogen Streptococcus pneumoniae, we identified 130 open reading frames encoding proteins with secretion motifs or similarity to predicted virulence factors. Mice were immunized with 108 of these proteins, and 6 conferred protection against disseminated S. pneumoniae infection. Flow cytometry confirmed the surface localization of several of these targets. Each of the six protective antigens showed broad strain distribution and immunogenicity during human infection. Our results validate the use of a genomic approach for the identification of novel microbial targets that elicit a protective immune response. These new antigens may play a role in the development of improved vaccines against S. pneumoniae.

Amino Acid Sequence↗