Little is known about the genetic contribution to cigarette smoking and nicotine addiction in Egypt. The dopamine D2 receptor gene contains a TaqI repeat fragment length polymorphism creating two alleles with functional significance, DRD2*A1 and DRD2*A2. We investigated the relationship between these alleles and tobacco use in a study of 389 Egyptian male current smokers (mean age = 40 years; SD = 12). Participants were interviewed in 2004 on their smoking behaviors and quit attempts, and were given the Fagerstr?m Test for Nicotine Dependence (FTND). Blood samples were obtained and genotyped for DRD2 A1and A2 alleles. The frequencies of A1/A2, A1/A2, and A2/A2 genotypes were 6%, 29%, and 65%, respectively. We found no statistically significant association between genotype and age at onset of smoking, years of smoking, FTND score, or average number of cigarettes smoked per day. DRD2 genotype was associated with the number of cigarettes smoked in the past 48 hr (42.2 in A1 carriers vs. 37.6 in A2, p = .03), the previous quit duration (28% in A1 vs. 40% in A2 quit for more than 1 month, p = .05), and the depth of inhalation (82% in A1 vs. 72% in A2 inhaled the smoke deeply, p = .03). Logistic regression analysis including DRD2 genotype, FTND score, age at smoking initiation, marital status, and education as predictors showed that maximum duration of quit time was associated with FTND score (p = .003), DRD2 genotype (p = .01), marital status (p = .03), and age at smoking initiation (p = .04). These findings suggest a modest association between DRD2 genotype and quitting behavior in male cigarette smokers in Egypt. 相似文献
This paper presents a new strategy for automating three-dimensional miniaturized manipulators using a visual feedback. This automation scheme can be used to handle the challenges associated with manipulation of minute soft components such as biological entities. The developed vision control system combines a depth and planar motion control using a single camera and an auto focus algorithm. This visual process was conducted by applying image segmentation and probe recognition along with depth alignment. To demonstrate the feasibility, reliability and robustness of this newly proposed strategy, extensive computer simulations were performed on images of a Zyvex® nanomanipulator obtained using a Scanning Electron Microscope (SEM). Also, a prototype manipulator with a visual feedback and an automatic controller was constructed and tested using soft elements. The results showed good accuracy and robustness of the end-effector recognition, positioning and aligning without occlusion difficulties. 相似文献
Summary: Composite films were prepared from a mixture of poly(vinyl acetate) latex and SWNTs. SEM images reveal a segregated SWNT network that grows heavier with increasing concentration. Nanotube segregation is the result of excluded volume created by the much larger polymer particles in the latex. Thermal conductivity exhibits a sharp rise with increasing quantity of nanotubes, although the maximum value is only 10% greater than that of the polymer matrix due to large thermal interface resistance. Storage modulus exhibits a peak and subsequent drop due to pore formation. In the absence of porosity, the Halpin‐Tsai model accurately predicts the composite modulus at 25 °C. The segregated network improves the composite modulus above Tg by nearly an order of magnitude with only 2 wt.‐% SWNT.
Schematic illustration of a segregated network of carbon nanotubes. 相似文献
Intraerythrocytic malaria parasites produce vast amounts of lactic acid through glycolysis. While the egress of lactate is very rapid, the mode of extrusion of H+ is not known. The possible involvement of a Na+/H+ antiport in the extrusion of protons across the plasma membrane of Plasmodium falciparum has been investigated by using the fluorescent pH probe 6-carboxyfluorescein. The resting cytosolic pH was 7.27 +/- 0.1 in ring stage parasites and 7.31 +/- 0.12 in trophozoites. Spontaneous acidification of parasite cytosol was observed in Na(+)-free medium and realkalinization occurred upon addition of Na+ to the medium in a concentration-dependent manner, with no apparent saturation. The rate of H(+)-efflux at the ring stage was higher than that at the trophozoite stage due to the larger surface/volume ratio of the young parasite stage. Na(+)-dependent H(+)-efflux was: 1) inhibited by the Na+/H+ inhibitors amiloride and 5-(N-ethyl-N-isopropyl) amiloride (EIPA), though at relatively high concentrations; 2) augmented with rising pH6 (pHi = 6.2, [Na+]o = 30 mM); and 3) decreased with increasing pHi (pHo = 7.4; [Na+]o = 30 mM). The pHi and the pHo dependencies of H(+)-efflux were almost identical at all parasite stages. Only at pHi > 7.6 efflux was totally obliterated. The target of this inhibitory effect is probably other than the antiport. Results indicate that H(+)-egress is mediated by a Na+/H+ antiport which is regulated by host and parasite pH and by the host cytosol sodium concentration. The proton transport capacity of the antiport can easily cope with all the protons of lactic acid produced by parasite's glycolysis. 相似文献
Resonant frequencies of the two-dimensional plasma in field effect transistors (FETs) increase with the reduction of the channel dimensions and can reach the Terahertz (THz) range. Nonlinear properties of the plasma/electron gas in the transistor channel can be used for the rectification and detection of THz radiation. The excitation of plasma waves by sub-THz and THz radiation was demonstrated for short gate transistors at cryogenic temperatures. At room temperature plasma oscillations are usually overdamped, but the FETs can still operate as efficient broadband rectifiers/detectors in the THz range. We present a few recent experimental results on THz detection by FETs showing some new ways of improvement of FETs for THz imaging at room temperature as well as the new physical phenomena like detection in quantizing magnetic fields. We also demonstrate THz emission properties of GaN based FETs. 相似文献
Damage of adjacent bridge structures due to relative responses, such as pounding and unseating, have been observed in many earthquakes. The isolators in bridge structures are effective in mitigating the induced seismic forces. However, the deck displacement becomes excessively large when subjected to ground motion with unexpected characteristics. This increases the possibility of pounding; and contributes to the unseating of bridge decks and subsequent collapse. An analytical model of expansion joints, that takes account of the interaction between adjacent bridge segments and the effect of impact and restrainers, is developed and nonlinear time history analyses are performed on a typical isolated multi-span bridge using three standard ground motions. The numerical simulation results show that pounding between adjacent bridge segments could amplify the relative displacement, resulting in the requirement of using an unseating prevention system. Restrainers are substantially effective in reducing the relative opening displacements and impact forces due to pounding at the expansion joints. However, the impact and the stretch of cable restrainers at expansion joints results in a large lateral force transfer from one deck to the other, which, consequently, significantly changes the global response of the participating structural systems. Therefore, it is effective to provide a shock absorber for the mitigation of impact effects between bridge segments or at the restrainers’ ends. The sudden changes of stiffness during poundings can be smoothed by using a natural rubber shock absorber, which prevents, to some extent, the acceleration peaks due to impact. The reaction forces at the pier bases and the pounding forces exerted on the superstructure can be satisfactorily reduced. 相似文献
A series of block poly(ester-ether urethane)s, poly(PHB/PCL-PEG-PCL), based on poly(3-hydroxybutyrate) (PHB-diol), as hard segments, and poly(ε-caprolactone)-b-poly(ethylene glycol)-b-poly(ε-caprolactone), (PCL-PEG-PCL) triblock copolydiol, as soft segments, were prepared using 1,6-hexamethylene diisocyanate (HDI), as non-toxic connecting agent. Polyurethanes block copolymer was synthesized from bacterial PHB and PCL-PEG-PCL blocks. The chemical structure and molecular weights of polymers prepared were characterized by FTIR, 1H NMR and GPC. The effect of chemical structure on the thermal and mechanical properties was studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile testing. The DSC results revealed that poly(PHB/PCL-PEG-PCL) urethanes are semi-crystalline with two crystallizable PHB and PCL-PEG-PCL blocks. The thermal stability of the urethanes is less than neat PHB. The results of tensile testing showed that the extensibility of PHB is largely enhanced by the incorporation of PCL-PEG-PCL soft segments. Activation energy Ea, as a kinetic parameter of thermal decomposition, was estimated by each of the Ozawa and Kissinger methods. Close values of activation energy were obtained by both methods. The swelling behaviour of the copolymers was also investigated. 相似文献