Silicon nanowire devices

Transport measurements were carried out on 15–35 nm diameter silicon nanowires grown using SiH4 chemical vapor deposition via Au or Zn particle-nucleated vapor-liquid-solid growth at 440°C. Both Al and Ti/Au contacts to the wires were investigated. The wires, as produced, were essentially intrinsic, although Au nucleated wires exhibited a slightly higher conductance. Thermal treatment of the fabricated devices resulted in better electrical contacts, as well as diffusion of dopant atoms into the nanowires, and increased the nanowire conductance by as much as 10^4. Three terminal devices indicate that the doping of the wires is p type

Fundamental study of the design and development of iron based alloys for biodegradable implant device applications

Biodegradable metals have been widely studied in recent years as potential biomedical implant materials which exhibit higher mechanical properties than degradable polymers while corroding over time to alleviate known complications such as stress-shielding, infection, permanent physical irritation and secondary removal/revision surgeries that is inherent to permanent and bio-inert metallic biomaterials. Specifically, iron (Fe), magnesium (Mg), and their alloys are the two main classes of metals that have been considered as promising candidates for degradable load and non-load bearing bone implants, cardiovascular stents, and other implantable medical devices. However, most of the research on Fe and Fe based alloys have reported very slow degradation rate in physiological environments while Mg and Mg based alloys under rapid degradation. Hence, controlling the degradation rates of these metals has been a key challenge limiting the technological development and implementation of these systems requiring more fundamental studies to be conducted. There is therefore the need to modify the chemical composition and microstructural characteristics through the appropriate alloying techniques with suitable alloying elements. Some studies have been conducted to overcome these limitations but the degradation rates and cytocompatibility of the two main classes of metals are still far from levels necessary for implementation in clinical applications. An alternative approach is therefore needed to develp metallic materials with improved degradation behavior wihle maintaining ithe desired biocompatibility. Although Fe and Mg have been studied separately as degradable implants, there are no reports on the Fe-Mg binary alloy system for use as biodegradable metallic materilas because of the thermodynamic immiscibility of Fe and Mg under ambient conditions. In this dissertation, novel non-equilibrium alloys, particularly in the Fe-Mg binary system with additional elements, have been proposed and studied for their desirable corrosion and cytocompatible properties. The first part of this dissertation focuses on the formation of amorphous alloys in the Fe-Mg binary alloy system through the process of high energy mechanical alloying (HEMA) followed by pulsed laser deposition (PLD) in order to overcome the limitations of the immiscibility of Fe-Mg. In the second part of this dissertation, an alloy development strategy to accomplish high degradation rates, antiferromagnetic behavior and good cytocompatibility is presented. Thus, manganese (Mn), calcium (Ca) and zirconium (Zr) were selected and added as alloying elements, which include the following two aspects: (i) Electrochemical considerations to increase the corrosion rates by electrochemical modification of the Fe matrix; (ii) addition of Mn to introduce anti-ferromagnetic characteristics to the alloy for exploring biological applications. Powders and thin layers were characterized for their composition/structure and evaluated potential for biomedical applications using preliminary in vitro cytocompatibility and corrosion experiments. For Fe-Mg binary alloy, uniform corrosion of Fe70Mg30 amorphous thin layer was observed and the corrosion current density value was approximately 8 fold higher than pure Fe. The direct and indirect cytotoxicity results indicated that Fe70Mg30 amorphous thin layer has no cytotoxicity to MC3T3-E1, hMSCs, HUVECs and NIH3T3 cell lines. Similarly, addition of Ca, Zr and Mn indicate good cytocompatibility with suitable modifications in the corrosion rate

Statistical analysis of IMRT dosimetry quality assurance measurements for local delivery guideline

<p>Abstract</p> <p>Purpose</p> <p>To establish our institutional guideline for IMRT delivery, we statistically evaluated the results of dosimetry quality assurance (DQA) measurements and derived local confidence limits using the concept confidence limit of |mean|+1.96σ.</p> <p>Materials and methods</p> <p>From June 2006 to March 2009, 206 patients with head and neck cancer, prostate cancer, liver cancer, or brain tumor were treated using LINAC-based IMRT technique. In order to determine site specific DQA tolerances at a later stage, a hybrid plan with the same fluence maps as in the treatment plan was generated on CT images of a cylindrical phantom of acryl. Points of measurement using a 0.125 cm³ion-chamber were typically located in the region of high and uniform doses. The planar dose distributions perpendicular to the central axis were measured by using a diode array in solid water with all fields delivered, and assessed using gamma criteria of 3%/3 mm. The mean values and standard deviations were used to develop the local confidence and tolerance limits. The dose differences and gamma pass rates for the different treatment sites were also evaluated in terms of total monitor uints (MU), MU/cGy, and the number of PTV's pieces.</p> <p>Results</p> <p>The mean values and standard deviations of ion-chamber dosimetry differences between calculated and measured doses were -1.6 ± 1.2% for H&N cancer, -0.4 ± 1.2% for prostate and abdominal cancer, and -0.6 ± 1.5% for brain tumor. Most of measured doses (92.2%) agreed with the calculated doses within a tolerance limit of ±3% recommended in the literature. However, we found some systematic under-dosage for all treatment sites. The percentage of points passing the gamma criteria, averaged over all treatment sites was 97.3 ± 3.7%. The gamma pass rate and the agreement of ion-chamber dosimetry generally decreased with increasing the number of PTV's pieces, the degree of modulation (MU/cGy), and the total MU beyond 700. Our local confidence limits were comparable to those of AAPM TG 119 and ESTRO guidelines that were provided as a practical baseline for center-to-center commissioning comparison. Thus, our institutional confidence and action limits for IMRT delivery were set into the same levels of those guidelines.</p> <p>Discussion and Conclusions</p> <p>The systematic under-dosage were corrected by tuning up the MLC-related factors (dosimetric gap and transmission) in treatment planning system (TPS) and further by incorporating the tongue-and groove effect into TPS. Institutions that have performed IMRT DQA measurements over a certain period of time need to analyze their accrued DQA data. We confirmed the overall integrity of our IMRT system and established the IMRT delivery guideline during this procedure. Dosimetric corrections for the treatment plans outside of the action level can be suggested only with such rigorous DQA and statistical analysis.</p

Tonicity response element binding protein associated with neuronal cell death in the experimental diabetic retinopathy

AIM: To study the contribution of tonicity response element binding protein (TonEBP) in retinal ganglion cell (RGC) death of diabetic retinopathy (DR). METHODS: Diabetes was induced in C57BL/6 mice by five consecutive intraperitoneal injections of 55 mg/kg streptozotocin (STZ). Control mice received vehicle (phosphate -buffered saline). All mice were killed 2mo after injections, and the extent of cell death and the protein expression levels of TonEBP and aldose reductase (AR) were examined. RESULTS: The TonEBP and AR protein levels and the death of RGC were significantly increased in the retinas of diabetic mice compared with controls 2mo after the induction of diabetes. Terminal deoxynucleotidyl transferase (TdT) -mediated dUTP nick end labeling (TUNEL) -positive signals co -localized with TonEBP immunoreactive RGC. These changes were increased in the diabetic retinas compared with controls. CONCLUSION: The present data show that AR and TonEBP are upregulated in the DR and TonEBP may contribute to apoptosis of RGC in the DR.close2

Surgical repair of descending thoracic and thoracoabdominal aortic aneurysm involving the distal arch: Open proximal anastomosis under deep hypothermia versus arch clamping technique

BackgroundSurgical repair of a descending thoracic and thoracoabdominal aortic aneurysm (DTA/TAAA) involving the distal arch is challenging and requires either deep hypothermic circulatory arrest (DHCA) or crossclamping of the distal arch. The aim of this study was to compare these 2 techniques in the treatment of DTA/TAAA involving the distal arch.MethodsFrom 1994 to 2012, 298 patients underwent open repair of DTA/TAAA through a left thoracotomy. One hundred seventy-four patients with distal arch involvement who were suitable for either DHCA (n = 81) or arch clamping (AC; n = 93), were analyzed. In-hospital outcomes were compared using propensity scores and inverse-probability-of-treatment weighting adjustment to reduce treatment selection bias.ResultsEarly mortality was 11.1% in the DHCA group and 8.6% in the AC group (P = .58). Major adverse outcomes included stroke in 16 patients (9.2%), low cardiac output syndrome in 15 (8.6%), paraplegia in 10 (5.7%), and multiorgan failure in 10 (5.7%). After adjustment, patients who underwent DHCA were at similar risk of death (odds ratio [OR], 1.14; P = .80) and permanent neurologic injury (OR, 0.95; P = .92) to those who underwent AC. Although prolonged ventilator support (>24 hours) was more frequent with DHCA than with AC (OR, 2.60; P = .003), DHCA showed a tendency to lower the risk of paraplegia (OR, 0.15; P = .057).ConclusionsCompared with AC, DHCA did not increase postoperative mortality and morbidity, except for prolonged ventilator support. However, DHCA may offer superior spinal cord protection to AC during repair of DTA/TAAA involving the distal arch

Comparison of implant stability after different implant surface treatments in dog bone

OBJECTIVES: The purpose of this investigation was to evaluate the effects of different implant surface treatments on implant stability in dog mandibles. MATERIAL AND METHODS: A total of 30 implants (Dentium Co, Seoul, Korea) were placed in 5 dog mandibles. Bone quality was assessed at each site. Implant stability was evaluated using 2 different methods. An OsstellTM resonance frequency analyzer (RFA) was used to determine the stability at baseline (day 1), and 3, 6 and 10 weeks after surgery. Animals were euthanized 10 weeks after implant installation. Specimens were obtained and submitted to the laboratory processing. Sections were stained with hematoxylin and eosin for histologic and histomorphometric analyses. All implantation sites in dog mandibles demonstrated bone types II and III. RESULTS AND CONCLUSIONS: All implants showed good primary stability at baseline in terms of insertion torque. The results of this study suggest that surface treatment may have significant effects on biological stability 3 weeks after implant placement. Further studies are needed to confirm these initial observations in poor quality bone

System Coverage and Capacity Analysis on Millimeter-Wave Band for 5G Mobile Communication Systems with Massive Antenna Structure

The use of a millimeter-wave band defined as a 30–300 GHz range is significant element for improving performance of 5th generation (5G) mobile communication systems. However, since the millimeter-wave signal has peculiar propagation characteristics especially toward non-line-of-sight regions, the system architecture and antenna structure for 5G mobile communications should be designed to overcome these propagation limitations. For realization of the 5G mobile communications, electronics and telecommunications research institute (ETRI) is developing central network applying various massive antenna structures with beamforming. In this paper, we have introduced the central network and evaluated the system coverage and capacity through C++ language-based simulations with real geospatial information