Electrical Conductivity Studies on Individual Conjugated Polymer Nanowires: Two-Probe and Four-Probe Results

<p>Abstract</p> <p>Two- and four-probe electrical measurements on individual conjugated polymer nanowires with different diameters ranging from 20 to 190 nm have been performed to study their conductivity and nanocontact resistance. The two-probe results reveal that all the measured polymer nanowires with different diameters are semiconducting. However, the four-probe results show that the measured polymer nanowires with diameters of 190, 95&#8211;100, 35&#8211;40 and 20&#8211;25 nm are lying in the insulating, critical, metallic and insulting regimes of metal&#8211;insulator transition, respectively. The 35&#8211;40 nm nanowire displays a metal&#8211;insulator transition at around 35 K. In addition, it was found that the nanocontact resistance is in the magnitude of 10⁴&#937; at room temperature, which is comparable to the intrinsic resistance of the nanowires. These results demonstrate that four-probe electrical measurement is necessary to explore the intrinsic electronic transport properties of isolated nanowires, especially in the case of metallic nanowires, because the metallic nature of the measured nanowires may be coved by the nanocontact resistance that cannot be excluded by a two-probe technique.</p

Cerebral aneurysm exclusion by CT angiography based on subarachnoid hemorrhage pattern: a retrospective study

<p>Abstract</p> <p>Background</p> <p>To identify patients with spontaneous subarachnoid hemorrhage for whom CT angiography alone can exclude ruptured aneurysms.</p> <p>Methods</p> <p>An observational retrospective review was carried out of all consecutive patients with non-traumatic subarachnoid hemorrhage who underwent both CT angiography and catheter angiography to exclude an aneurysm. CT angiography negative cases (no aneurysm) were classified according to their CT hemorrhage pattern as "aneurismal", "perimesencephalic" or as "no-hemorrhage."</p> <p>Results</p> <p>Two hundred and forty-one patients were included. A CT angiography aneurysm detection sensitivity and specificity of 96.4% and 96.0% were observed. All 35 cases of perimesencephalic or no-hemorrhage out of 78 CT angiography negatives also had negative angiography findings.</p> <p>Conclusions</p> <p>CT angiography is self-reliant to exclude ruptured aneurysms when either a perimesencephalic hemorrhage or no-hemorrhage pattern is identified on the CT within a week of symptom onset.</p

Epidural analgesia with dexmedetomidine, alone or in combination with ropivacaine, in dogs undergoing tibial plateau leveling osteotomy (TPLO)

The analgesic efficacy of dexmedetomidine administered epidurally in dogs undergoing TPLO was compared in a prospective, randomized, blinded study. Thirty client-owned dogs undergoing TPLO were assigned to one of three epidural treatments (10 dogs each): group R (1 mg kg-1 0.5% ropivacaine), group RD (1 mg kg-1 0.5% ropivacaine and 2.5 µg kg-1 0.05% dexmedetomidine) and group D (2,5 µg kg-1 0.05% dexmedetomidine). Dilution was performed with sterile 0.9% saline to maintain a total volume of 0.2 mL kg-1. Nociception was assessed intra-operatively based on changes in HR, fr and MAP. When two of these parameters increased by more than 20% from baseline values, rescue fentanyl was administered IV (3 µg kg-1). Post-operative pain was assessed using the Glasgow composite pain scale (GCPS; Holton et al. 2001) and a visual analogue scale (VAS). Sedation was scored recorded using a modified Ramsey sedation scale (Ramsey et al. 1974). The medians of intra-operative physiologic parameters and post-operative pain scores were analyzed with Kruskal–Wallis, followed by Bonferroni tests. No dogs in RD, 2 dogs in R and 2 dogs in D required fentanyl. Postoperative sedation scores tended to be higher (p = 0.09) in groups D and RD as compared to group R. Postoperative analgesia scores were similar in all groups (GCPS p = 0.57; VAS p = 1.00). No significant differences were observed among the remaining parameters. Epidural dexmedetomidine at the dosage of 2.5 µg kg-1, alone or in combination with ropivacaine, provided a good perioperative analgesia in dogs undergoing TPLO

Temporal and regional evolution of aquaporin-4 expression and magnetic resonance imaging in a rat pup model of neonatal stroke

Edema formation can be observed using magnetic resonance imaging (MRI) in patients with stroke. Recent studies have shown that aquaporin-4 (AQP4), a water channel, is induced early after stroke and potentially participates in the development of brain edema. We studied whether induction of AQP4 correlated with edema formation in a rat pup filament stroke model using high field (11.7-Tesla) MRI followed by immunohistochemical investigation of AQP4 protein expression. At 24 h, we observed increased T2 values and decreased apparent diffusion coefficients (ADC) within injured cortical and striatal regions that reflected the edema formation. Coincident with these MR changes were significant increases in AQP4 expression on astrocytic end-feet in the border regions of injured tissues. Striatal imaging findings were still present at 72 h with a slow normalization of AQP4 expression in the border regions. At 28 d, AQP4 expression normalized in the border while in this region ADC values increased. We show that induction of AQP4 is increased during the period of active edema formation in the border region without regional correlation with edema. Finally, induction of AQP4 on astrocyte end-feet could participate in tissue preservation after ischemia in the immature rat brain