Exponentially selective molecular sieving through angstrom pores.

Two-dimensional crystals with angstrom-scale pores are widely considered as candidates for a next generation of molecular separation technologies aiming to provide extreme, exponentially large selectivity combined with high flow rates. No such pores have been demonstrated experimentally. Here we study gas transport through individual graphene pores created by low intensity exposure to low kV electrons. Helium and hydrogen permeate easily through these pores whereas larger species such as xenon and methane are practically blocked. Permeating gases experience activation barriers that increase quadratically with molecules' kinetic diameter, and the effective diameter of the created pores is estimated as ∼2 angstroms, about one missing carbon ring. Our work reveals stringent conditions for achieving the long sought-after exponential selectivity using porous two-dimensional membranes and suggests limits on their possible performance.

The effect of silencing arginine kinase by RNAi on the larval development of Helicoverpa armigera.

Arginine kinase (AK) is an important regulation factor of energy metabolism in invertebrate. An arginine kinase gene, named HaAK, was identified to be differentially expressed between Cry1Ac-susceptible (96S) and Cry1Ac-resistant (Bt-R) Helicoverpa armigera larvae using cDNA-amplification fragment length polymorphism analysis. The full-length open reading frame sequence of HaAK gene with 1068 bp was isolated from H. armigera. Quantitative reverse transcription polymerase chain reaction assay revealed that HaAK gene is specifically expressed in multiple tissues and at larval developmental stages. The peak expression level of HaAK was detected in the midgut of the fifth-instar larvae. Moreover, the expression of HaAK was obviously down-regulated in Bt-R larvae. We further constructed a dsRNA vector directly targeting HaAK and employed RNAi technology to control the larvae. The feeding bioassays showed that minute quantities of dsRNA could greatly increase the larval mortality and delay the larval pupation. Silencing of HaAK significantly retarded the larval development, indicating that HaAK is a potential target for RNA interference-based pest management.

Early contribution of arterial wave reflection to left ventricular relaxation abnormalities in a community-dwelling population of normotensive and untreated hypertensive men and women.

We examined the contribution of arterial wave reflection to early abnormalities in left ventricular relaxation, whether this association was modified by gender or hypertension and the role of reflected wave timing and amplitude. We studied a cohort of normotensive and untreated essential hypertensive Taiwanese participants (675 men, 601 women, mean age 52 years). Doppler flow and applanation tonometry were performed to assess carotid-femoral pulse wave velocity (PWV) and augmentation index (AI). Diastolic parameters including the ratio between the peak velocity of early and late diastolic mitral inflow (E/A), E-deceleration time and left atrial (LA) diameter were measured by echocardiography. In multivariate models predicting E/A, women were more likely to have lower E/A than men (ß=-0.08, P<0.001). AI was significantly associated with lower E/A in both men (ß=-0.09, P=0.005) and women (ß=-0.12, P<0.001) independent of PWV. Inclusion of AI in the overall model reduced the gender difference in E/A by 61% and rendered it nonsignificant. There was a significant interaction between AI and hypertension (P=0.02). The inverse association between AI and E/A was significant only in normotensive men and women, and only for the amplitude but not timing of the reflected wave. In conclusion, the contribution of wave reflection to left ventricular diastolic dysfunction was independent of arterial stiffness, more pronounced in normotensive individuals and explained a significant portion of the gender difference in diastolic function.

Comparison of two generalized transfer functions for measuring central systolic blood pressure by an oscillometric blood pressure monitor.

Central aortic systolic blood pressure (SBP-C) can be estimated from a cuff oscillometric waveform derived during the pulse volume plethysmography (PVP) by applying a device-specific aortic pressure-to-PVP waveform-generalized transfer function (A2P(GTF)). The present study compared the performance of an aortic-to-brachial pressure waveforms generalized transfer function (A2B(GTF)), which is independent of any PVP devices, with an A2P(GTF). Generalized transfer function of aortic-to-brachial (A2B(GTF)) and aortic-to-PVP (A2P(GTF)) were generated from the simultaneously obtained central aortic and brachial pressure waveforms recorded by a high-fidelity dual pressure sensor catheter, and the PVP waveform recorded by a customized noninvasive blood pressure monitor during cardiac catheterization in 40 patients, and were then applied in another 100 patients with simultaneously recorded invasive aortic pressure and noninvasively calibrated (using cuff SBP and diastolic blood pressures) PVP waveforms. The mean difference±s.d. between the noninvasively estimated and invasively recorded SBP-C was -2.1±7.7 mm Hg for A2B(GTF), which was not greater than that of -3.0±7.7 mm Hg for A2P(GTF) (P<0.01). In conclusion, SBP-C can be measured reliably using a noninvasive blood pressure monitor by applying either an A2P(GTF) or A2B(GTF) to a noninvasively calibrated PVP waveform. The performance of an A2B(GTF) is not inferior to that of an A2P(GTF).

Determinants of pressure wave reflection: characterization by the transit time-independent reflected wave amplitude.

The effects of pressure wave reflection have been incompletely described by the central augmentation index (cAI) and augmented pressure (Pa). We therefore investigated the determinants of amplitude of the reflected wave (Pb), which is independent of the reflected wave transit time (RWTT) and has been shown to predict cardiovascular mortality in the general population. A total of 180 (117 men, mean age 68 years old) patients were recruited. Carotid pressure waveforms derived by tonometry at baseline and 3 min after administration of sublingual nitroglycerin (NTG) were calibrated and then decomposed into the forward and backward waves to yield Pb. The ratio of pre-ejection period/ejection time (PEP/ET) was measured. By stepwise multivariate analysis, independent determinants of Pb included brachial mean blood pressure (ß=0.56, P<0.001), heart rate (ß=-0.29, P<0.001), age (ß=0.20, P<0.001), PEP/ET (ß=-0.16, P=0.004) and height (ß=-0.13, P=0.018). RWTT, body mass index and sex were significant independent determinants of Pa and cAI but did not contribute to Pb. Change of Pb but not Pa or cAI significantly predicted the changes of carotid systolic (r=0.550, P<0.001) and pulse pressure (r=0.618, P<0.001) after NTG. In conclusion, determinants of Pb differ from those of cAI and Pa. Pb is independent of sex and RWTT.

Coronary artery air embolism: a potentially fatal complication of CT-guided percutaneous lung biopsy.

CT-guided transthoracic lung biopsy is becoming a widely accepted procedure for the diagnosis of pulmonary lesions. The rate of severe complications following such a procedure has been reported. Of these complications, air embolism is the most likely to be fatal. We report a case of right coronary air embolism resulting in myocardial infarction after a CT-guided percutaneous needle biopsy of the lung. The patient died from underlying malignant disease 4 months later.

Polarized raman study of single-wall semiconducting carbon nanotubes

Polarized Raman spectra were obtained from a rope of aligned semiconducting single-wall nanotubes (SWNTs) in the vicinity of the D band and the G band. Based on group theory analysis and related theoretical predictions, the G-band profile was deconvolved into four intrinsic SWNT components with the following symmetry assignments: 1549 cm(-1) [E2(E(2g))], 1567 cm(-1) [A(A(1g))+E1(E(1g))], 1590 cm(-1) [A(A(1g))+E1(E(1g))] and 1607 cm(-1) [E2(E(2g))]. The frequency shifts of the tangential G modes from the 2D graphitelike E(2g(2)) frequency are discussed in terms of the nanotube geometry.

Hydrogen storage in single-walled carbon nanotubes at room temperature

Masses of single-walled carbon nanotubes (SWNTs) with a large mean diameter of about 1.85 nanometers, synthesized by a semicontinuous hydrogen arc discharge method, were employed for hydrogen adsorption experiments in their as-prepared and pretreated states. A hydrogen storage capacity of 4.2 weight percent, or a hydrogen to carbon atom ratio of 0.52, was achieved reproducibly at room temperature under a modestly high pressure (about 10 megapascal) for a SWNT sample of about 500 milligram weight that was soaked in hydrochloric acid and then heat-treated in vacuum. Moreover, 78.3 percent of the adsorbed hydrogen (3.3 weight percent) could be released under ambient pressure at room temperature, while the release of the residual stored hydrogen (0.9 weight percent) required some heating of the sample. Because the SWNTs can be easily produced and show reproducible and modestly high hydrogen uptake at room temperature, they show promise as an effective hydrogen storage material.