[Effectiveness of the "14 plus 7 day quarantine" and "nucleic acid plus total antibody testing" strategy for screening imported patients with COVID-19 in Xiamen]

Objective: To analysis effectiveness of the "14 plus 7 day quarantine" and "nucleic acid plus total antibody testing" strategy (combined screening strategy) for screenin the imported patients with COVID-19 in Xiamen. Methods: The study populations were overseas travelers arriving in Xiamen from March 17 to December 31, 2020, and overseas travelers who had quarantine outside Xiamen for less than 21 days from July 18 to December 31, 2020. Data were collected and analyzed on the timing of detection, pathways, and test results of the imported patients with COVID-19 after implementing combined screening strategy. Results: A total of 304 imported patients with COVID-19 were found from 174 628 overseas travelers and 943 overseas travelers from other cities. A total of 163 cases (53.6%) were diagnosed by multitime, multisite intensive nucleic acid testing after positive finding in total antibody testing. Among them, 27 (8.9%) were first positive for nucleic acid in 14 plus 7 day quarantine and 136 were first positive for nucleic acid in 14-day quarantine. Only 8 of these individuals were tested positive for nucleic acid after positive total antibody testing. The other 128 individuals were tested positive for nucleic acid after being negative for average 2.3 times (maximum of 6 times). Aditional 155 cases might be detected by using the combined "14 plus 7 day quarantine" and " nucleic acid plus total antibody testing" strategy compared with "14-day quarantine and nucleic acid testing" strategy, accounting for 51.0% of the total inbound infections. So the combined screening strategy doubled the detection rate for imported patients with COVID-19. No second-generation case caused by overseas travelers had been reported in Xiamen as of February 26, 2021. Conclusions: Xiamen's combined screening strategy can effectively screen the imported patients with COVID-19 who were first positive for nucleic acid after 14 day quarantine. Compared with "14 day quarantine and nucleic acid testing", the combined screening strategy improved detection rate and further reduced the risk of the secondary transmission caused by the imported patients with COVID-19.

[Simultaneous combined radical surgery for hepatic and renal alveolar echinococcosis: an analysis of 10 clinical cases]

Objective: To examine the feasibility, safety and efficacy of simultaneous combined radical surgery for hepatic and renal alveolar echinococcosis (AE). Methods: Clinical dates of consecutive 10 hepatic and renal AE patients who accepted surgical treatment in the First Affiliated Hospital of Xinjiang Medical University during April 2013 to September 2019 were analyzed retrospectively. There were 8 males and 2 females, aged (42.5±10.3) years (range: 27 to 52 years). Seven of them had previously palliative surgical treatment with poor compliance to post-operative medication. All of the patients had hepatic-renal combined AE lesions, and two of them had left lateral and left renal lesions for each, which sized for (726.4±576.1)cm³ (range: 117.0 to 1 998.0 cm³). Extra-hepatic or renal lesions infiltrated to right diaphragm, inferior vena cava, right adrenal gland, abdominal wall, right psoas muscle, duodenum wall and right pulmonary lobe (respectively were 7, 7, 6, 2, 1, 1, 2 cases). Surgery were performed mainly with simultaneous combined surgery and vascular reconstruction techniques for this series. Hemi-hepatectomy or extended right lobectomy was applied in 8 patients, while 2 other patients received ex vivo liver resection and autotransplantation, additionally, one patient had partial hepatectomy for left lateral lobular lesion. Total right nephrectomy, partial right nephrectomy and partial left nephrectomy were respectively performed on 7, 3 and 1 patient(s). Additionally, extra-hepatic or renal lesions were eradicated followed by relevant repairments or reconstructions. Results: Surgeries went well and there was no intra-or post-operative liver or renal dysfunction occurred. During recovery period, 3 cases experienced with hydrothorax and managed well after drainage and supportive treatment, and one patient developed peri-renal urinary leakage and cured by "J" catheter. The subjects were followed-up for 6 to 81 months (median: 21 months), no death, organ dysfunction, chronic or acute kidney diseases occurred. One case encountered with abdominal hernia at post-operative 7^th month and was successfully managed with laparoscopic repair with artificial mesh. No disease recurrence in all patients, which reached clinical cure at last. Conclusion: When complied strictly to indications, simultaneous combined radical surgery could be a feasible, safe and efficient approach for patients with hepatic and renal AE, which is primary or relapsed from previous hepatic AE surgery or interventional therapies as well as neighboring organ AE invasions.

[Exhaustion of CD8+ T cell immune functions in spleen of mice with different doses of Echinococcus multilocularis infections]

OBJECTIVE

To examine the changes in the immune functions of CD8⁺ T cells in the spleen of mice following Echinococcus multilocularis infections at various doses and at different time points.

METHODS

The E. multilocularis protoscoleces were collected, and E. multilocularis infection was modeled in mice via the hepatic portal vein at doses of 50 (low-dose), 500 (medium-dose) and 2 000 protoscoleces (high-dose), while physiological saline served as controls. Mouse spleen was isolated 2 (earlystage), 12 (middle-stage) and 24 weeks post-infection (late-stage), and spleen lymphocytes were harvested. The phenotype of memory CD8⁺ T cells and 2B4 expression were quantified in the mouse spleen, and the secretion of interferon (IFN)-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-17A and IL-10 was measured.

RESULTS

A central-memory phenotype was predominant in the CD8⁺ T cells in the spleen of mice at the early stage of high-dose protoscolece infections, and the proportion of central-memory CD8⁺ T cells was significantly greater in the high-dose group than in the control group (35.50% ± 2.00% vs. 25.90% ± 2.46%, P < 0.01), while a effector- memory phenotype was predominant in the CD8⁺ T cells in the spleen of mice at the late stage of medium- and high-dose protoscolece infections, and the proportions of effector-memory CD8⁺ T cells were significantly greater in the medium- (25.70% ± 4.12%) and high-dose group (28.40% ± 4.12%) than in the control group (10.50% ± 6.45%) (P < 0.05). The proportions of the central-memory CD8⁺ T cells were significantly higher in the high-dose group than at middle and late stages than at the early stage (P < 0.01), and the proportion of effector-memory CD8⁺ T cells was significantly greater in the high-dose group at the late stage than at early and middle stages (P < 0.05). The secretion of IFN-γ and IL-17A by spleen CD8⁺ T cells was elevated in the low- and medium-dose groups at the early stage of infection, and high-dose protoscolece infection promoted the secretion of IFN-γ and TNF-α by spleen CD8⁺ T cells; however, the levels of IFN-γ and TNF-α were significantly lower at the late stage than at the early and middle stages (P < 0.05). In addition, high 2B4 expression was detected in spleen CD8⁺ T cells in the middle- and high-dose groups at the late stage of infection, and the 2B4 expression was significantly higher in the medium(4.73% ± 1.56%) and high-dose groups (4.94% ± 1.90%) than in the low-dose group (2.49% ± 0.58%) and the control group (2.92% ± 0.60%) (P < 0.05).

CONCLUSIONS

E. multilocularis may be killed and eliminated through the host immune responses at the middle and late stages of low- and medium-dose protoscolece infections, while high-dose protoscolece infections may trigger the upregulation of 2B4 expression in mouse spleen CD8⁺ T cells at the late stage, which leads to immune exhaustion and the resultant chronic infections.

Dietary mannan oligosaccharide ameliorates cyclic heat stress-induced damages on intestinal oxidative status and barrier integrity of broilers

This study investigated protective effects of mannan oligosaccharide (MOS) inclusion on growth performance, intestinal oxidative status, and barrier integrity of cyclic heat-stressed broilers. A total of 240 one-day-old chicks were allocated into 3 treatments of 10 replicates each. Control broilers reared at a thermoneutral temperature were fed a basal diet, whereas broilers in heat stress and MOS groups raised at a cyclic high temperature (32 to 33°C for 8 h/d) were given the basal diet supplemented with 0 or 250 mg/kg MOS, respectively. Compared with control group, heat stress decreased (P < 0.05) average daily gain and feed conversion ratio during grower, finisher, and entire periods, average daily feed intake during finisher and entire periods, and ileal superoxide dismutase activity at 42 D, whereas increased (P < 0.05) rectal temperature at 21 and 42 D and jejunal malondialdehyde content at 42 D. Dietary MOS increased (P < 0.05) average daily gain, average daily feed intake, and feed conversion ratio during finisher and entire periods, but decreased (P < 0.05) jejunal malondialdehyde concentration of heat-stressed broilers at 42 D. Heat stress decreased (P < 0.05) jejunal villus height (VH) and claudin-3 gene expression at 21 D, and VH and VH: crypt depth (CD) ratio in jejunum and ileum as well as mRNA abundances of jejunal mucin 2 and occludin, and ileal mucin 2, zonula occludens-1, and occludin, and claudin-3 at 42 D, whereas increased (P < 0.05) serum D-lactate acid content at 21 and 42 D, and serum diamine oxidase activity and jejunal CD at 42 D. The MOS supplementation increased (P < 0.05) jejunal VH at 21 D, VH and VH: CD of jejunum and ileum at 42 D, mRNA abundances of jejunal occludin and ileal mucin 2, zonula occludens-1, and occludin at 42 D, whereas reduced (P < 0.05) ileal CD at 42 D. These results suggested that MOS improved growth performance, and oxidative status and barrier integrity in the intestine of broilers under cyclic heat stress.

Selective interface transparency in graphene nanoribbon based molecular junctions

A clear understanding of electrode-molecule interfaces is a prerequisite for the rational engineering of future generations of nanodevices that will rely on single-molecule coupling between components. With a model system, we reveal a peculiar dependence on interfaces in all graphene nanoribbon-based carbon molecular junctions. The effect can be classified into two types depending on the intrinsic feature of the embedded core graphene nanoflake (GNF). For metallic GNFs with |N_A - N_B| = 1, good/poor contact transparency occurs when the core device aligns with the center/edge of the electrode. The situation is reversed when a semiconducting GNF is the device, where N_A = N_B. These results may shed light on the design of real connecting components in graphene-based nanocircuits.

Bevacizumab and gefitinib enhanced whole-brain radiation therapy for brain metastases due to non-small-cell lung cancer

Non-small-cell lung cancer (NSCLC) patients who experience brain metastases are usually associated with poor prognostic outcomes. This retrospective study proposed to assess whether bevacizumab or gefitinib can be used to improve the effectiveness of whole brain radiotherapy (WBRT) in managing patients with brain metastases. A total of 218 NSCLC patients with multiple brain metastases were retrospectively included in this study and were randomly allocated to bevacizumab-gefitinib-WBRT group (n=76), gefitinib-WBRT group (n=77) and WBRT group (n=75). Then, tumor responses were evaluated every 2 months based on Response Evaluation Criteria in Solid Tumors version 1.0. Karnofsky performance status and neurologic examination were documented every 6 months after the treatment. Compared to the standard WBRT, bevacizumab and gefitinib could significantly enhance response rate (RR) and disease control rate (DCR) of WBRT (P<0.001). At the same time, RR and DCR of patients who received bevacizumab-gefitinib-WBRT were higher than those who received gefitinib-WBRT. The overall survival (OS) rates and progression-free survival (PFS) rates also differed significantly among the bevacizumab-gefitinib-WBRT (48.6 and 29.8%), gefitinib-WBRT (36.7 and 29.6%) and WBRT (9.8 and 14.6%) groups (P<0.05). Although bevacizumab-gefitinib-WBRT was slightly more toxic than gefitinib-WBRT, the toxicity was tolerable. As suggested by prolonged PFS and OS status, bevacizumab substantially improved the overall efficacy of WBRT in the management of patients with NSCLC.

[The clinical practice of improvement the "Volume and Quality" of functional liver in autologous liver transplantation for the patients with alveolar echinococcosis]

Objective: To investigate the clinical significance of accurate assessment of "volume and quality" of functional liver in Autologous liver transplantation (ALT) in the treatment of the advanced hepatic alveolar echinococcosis (HAE). Methods: The clinical data of 12 patients with advanced HAE who underwent ALT at the First Affiliated Hospital of Xinjiang Medical University from May 2015 to July 2016 were retrospectively analyzed. Results: The preoperative hepatic functions of 12 patients were 8 Child-Pugh Grade A, 1 Grade B, and 3 Grade C. Three of the patients had moderate or severe jaundice. Three of the patients calculated functional liver graft volume (GV) and standard liver volume (SLV) ratio (GV/SLV) were <30%. After the protection of liver function, anti-infection, percutaneous transhepatic cholangiography drainage (PTCD), selective portal vein embolization (PVE), and staging liver resection, liver function Child-Pugh grade of 11 patients was raised to A grade, and the other patient was B grade, meanwhile the bilirubin was reduced to 2 times the normal value. The GV/SLV ratios of 3 patients with low GV/SLV ratio had reached 44.4%, 47.2% and 56.2% respectively. In this study, the GV/SLV ratios of the 12 patients were between 73.2% and 40.8% with an average of 55.6%. Operation time was 11.5-20.5 h, with an average of 12.3 h. Anhepatic phase time was 193-375 min with median 253.5 min. The red blood cell suspension was 0-6 U during the operation. The average hospitalization was 10-42 d, with the average 22.7 d. Total hospital costs were 121 600-434 800 Yuan, with the median cost of 174 400 Yuan. One patient died of septic shock a week after surgery. Conclusion: (1)ALT may provide feasibility for the advanced HAE. (2)Accurate assessment of functional liver "volume and quality" appeared as the key points to the ALT. (3)Precise surgery and individualized treatment could improve and protect the functional liver "volume and quality" .

[The causes and adjustment methods of prenatal anxiety disorder during the Han and Tang Dynasties]

Though the title of prenatal anxiety disorder didn't mentioned in the literature of the Han and Tang Dynasties, the effect of anxiety on the fetus and its delivery were already recognized. The causes of anxiety were mainly the physical discomfort caused by pregnancy, or the worries about fetus sex, health, appearance, and its fate etc., or the fear of delivery. Although the adjustment methods were often tainted with superstition, yet it could ease the anxiety of pregnant women to some extent.

Chloroplast analysis of Zelkova schneideriana (Ulmaceae): genetic diversity, population structure, and conservation implications

Zelkova schneideriana is endemic to China and belongs to the Ulmaceae. It is listed as a Near Threatened species in the China Biodiversity Red Data Book. We conducted a phylogeographical study of two chloroplast regions (psbA-trnH and trnG-trnM) in several Chinese Z. schneideriana populations, in order to examine the genetic diversity, population structure, and evolutionary history of the species. In all, 10 haplotypes were detected. The population from Sangzhi, Hunan, had the highest nucleotide diversity (π = 0.00653) and haplotype diversity (HD = 1.000), and should be considered the most suitable population to be protected under an in situ conservation strategy. Seed collections from as many individuals as possible in other populations would preserve the genetic diversity of Z. schneideriana.

Tailoring the transmission lineshape spectrum of zigzag graphene nanoribbon based heterojunctions via controlling their width and edge protrusions

We report a first-principles analysis of electron transport through narrow zigzag graphene nanoribbon (up to 2.2 nm) based wedge-shaped heterojunctions. We show that the width difference between the electrode and the scattering region and the edge protrusion of heterojunctions can be tuned to endow the system's transmission spectrum with distinctive features. In particular, transport through junctions with a one sided protrusion in the scattering region is always dominated by a Breit-Wigner-type resonance right at the Fermi level, regardless of the large or small width difference. On the other hand, a junction with protrusions on both sides of the scattering region shows insulating behaviour near the Fermi level for a large width difference but weak transmission channels are formed at the core of the scattering region for a small width difference. When the protrusion is absent in the junction, transmission functions display rather complex structures: double peaks situating nearly symmetrically away from the Fermi level and a strongly asymmetric profile in the vicinity of the Fermi level are observed for large and small width differences, respectively. These results may shed light on the design of real connecting components in nanocircuits.

Isolation and characterization of polymorphic microsatellite loci from Zelkova schneideriana Hand.-Mazz

Zelkova schneideriana is a highly valued hardwood species. An improved technique for isolating codominant compound microsatellite markers was used to develop simple sequence repeat markers for Z. schneideriana. A total of 12 microsatellite loci were identified. Overall, the number of alleles per locus ranged from 8-19, with an average of 11.75. Observed heterozygosity and expected heterozygosity values ranged from 0.109-0.709 and 0.832-0.929, respectively. Polymorphic information content is from 0.803-0.915, with an average of 0.854. These markers will be very important for future research related to the genetic diversity, population structure, patterns of gene flow, and mating system of this species.

Oxygen vacancy diffusion in bare ZnO nanowires

Oxygen vacancies (VO) are known to be common native defects in zinc oxide (ZnO) and to play important roles in many applications. Based on density functional theory, we present a study for the migration of oxygen vacancies in ultra-thin ZnO nanowires (NWs). We find that under equilibrium growth conditions VO has a higher formation energy (Ef) inside the wire than that at shallow sites and surface sites, with different geometric relaxations and structural reconstructions. The migration of VO has lower barriers in the NW than in the bulk and is found to be energetically favorable in the direction from the bulk to the surface. These results imply a higher concentration of VO at surface sites and also a relative ease of diffusion in the NW structure. Our results support the previous experimental observations and are important for the development of ZnO-based devices in photocatalysis and optoelectronics.

Superposed pulse amplitude modulation for visible light communication

We propose and experimentally demonstrate a novel modulation scheme called superposed pulse amplitude modulation (SPAM) which is low-cost, insensitive to non-linearity of light emitting diode (LED). Multiple optical pulses transmit parallelly from different spatial position in the LED array and overlap linearly in free space to realize SPAM. With LED arrangement, the experimental results show that using the modulation we proposed the data rate of 120 Mbit/s with BER 1 × 10(-3) can be achieved with an optical blue filter and RC post-equalization.

Rhizoctonia solani Identified as the Disease Causing Agent of Peanut Leaf Rot in China

Peanut (Arachis hypogaea L.) is one of the most economically important oil crops in the world. Since the 1990s, the peanut industry has developed rapidly in China. However, because of the use of high-yield varieties and increased plant density, a peanut leaf rot disease occurred in Laixi Experimental Fields in Shandong Province, China in 2007. Leaves had nearly circular, brown lesions that enlarged quickly developing yellow-brown halos at the edges of the lesions. High relative humidity under field conditions led to complete necrosis of the leaves with cotton wool-like mycelia observed followed by the development of sclerotia on the leaf surface. Symptomatic plants were observed between 2007 and 2010, and symptomatic leaf tissue was collected from the Laixi Experimental Fields. An isolate (designated YF-1) from symptomatic peanut leaves was isolated and purified on potato dextrose agar (PDA) and water agar (WA) medium. On PDA, the colony appeared initially as colorless and grew to the diameter of a 9-cm petri dish within 3 days. As the mycelium aged, the colony color gradually became light brown, and sclerotia developed on the surface of the colony. YF-1 was identified as Rhizoctonia solani Kühn based on the number of nuclei per cell ranging from 4 to 13 (average 6.1), hyphal diameter being 7.5 to 12.9 μm (average 8.3 μm), branching at right angles, a septum was present near each hyphal branch with a slight constriction, and no clamp connection structures or conidia were ever observed (4). To further confirm the identity of isolate YF-1, genomic DNA was extracted using the DNeasy Plant Mini DNA Extraction Kit (Shanghai Leifeng Biotechnol. Co., Ltd.), and the complete internal transcribed spacer (ITS) region of ribosomal DNA was amplified and sequenced with a pair of primers ITS1/ITS4 (2). A GenBank BLAST search produced an exact match for the sequences of R. solani (AY154301), with 100% sequence similarity. To estimate the mode of anastomosis, YF-1 was paired on WA medium with each reference strain belonging to anastomosis groups (AGs) 1 through 8 (provided by Shandong Agriculture University) (1,3). The results indicated that YF-1 belonged to group AG-1, subgroup AG-1-IA of R. solani. Pathogenicity tests were conducted by inoculating 10 peanut leaves using a colonized paper disc method (filter paper 1 cm in diameter suspended in the mycelia suspension). Ten control leaves received paper discs without mycelium. Inoculated and non-inoculated plants were kept in humid chambers for 24 h at 25°C. Three days after inoculation, the leaves developed typical brown lesions that were similar to those of naturally diseased plants. Koch's postulates were fulfilled by reisolation of R. solani from symptomatic leaves. No symptoms were observed on control leaves. To our knowledge, this is the first report of peanut leaf rot caused by R. solani. Occurrence of the disease in China is a new threat to the health of peanut. References: (1) Y. X. Chen et al. Acta Phytopathol. Sin. 3:139, 1985. (2) T. Misawa and S. Kuninaga. J. Gen. Plant Pathol. 76:310, 2010. (3) A. Ogoshi. Ann. Phytopathol. Soc. Jpn. 38:117, 1972. (4) J. R. Jr. Pameter and H. S. Whitmey. UC Press. 135, 1970.

Enhanced removal of chemical oxygen demand, nitrogen and phosphorus using the ameliorative anoxic/anaerobic/oxic process and micro-electrolysis

Synthetic wastewater was treated using a novel system integrating the reversed anoxic/anaerobic/oxic (RAAO) process, a micro-electrolysis (ME) bed and complex biological media. The system showed superior chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) removal rates. Performance of the system was optimised by considering the influences of three major controlling factors, namely, hydraulic retention time (HRT), organic loading rate (OLR) and mixed liquor recirculation (MLR). TP removal efficiencies were 69, 87, 87 and 83% under the HRTs of 4, 8, 12 and 16 h. In contrast, HRT had negligible effects on the COD and TN removal efficiencies. COD, TN and TP removal efficiencies from synthetic wastewater were 95, 63 and 87%, respectively, at an OLR of 1.9 g/(L·d). The concentrations of COD, TN and TP in the effluent were less than 50, 15 and 1 mg/L, respectively, at the controlled MLR range of 75-100%. In this system, organics, TN and TP were primarily removed from anoxic tank regardless of the operational conditions.

Molecule-substrate interaction channels of metal-phthalocyanines on graphene on Ni(111) surface

Molecule-substrate interaction channels of metal-phthalocyanines (MPcs, including NiPc, CuPc, ZnPc, FePc, and CoPc) on graphene on Ni(111) were investigated by employing high-resolution electron energy loss spectroscopy (HREELS). Except the expected IR-active modes, some Raman-active modes were also observed in all of MPcs, which are considered in this study. From the origination of the Raman-active features, it was deduced that MPcs are coupled with the substrate mainly through their central metal atom. The Raman-active modes appear as symmetric peaks in the HREELS in the case of MPcs with Ni, Cu, and Zn, whereas they are asymmetric and appear as a Fano line shape in the case of MPcs with Fe and Co. This spectroscopic difference indicates that the molecule-substrate coupling is completely different in the two cases mentioned above. The molecule-substrate interaction strength is considerably weak and comparable with the π-π interaction between molecules in the case of MPcs with Ni, Cu, and Zn, whereas it is much stronger in the case of MPcs with Fe and Co. From the HREELS observations, it can be suggested that the whole molecule can be effectively decoupled from the underneath Ni(111) by inserting a single layer of graphene between them in the case of MPcs with Ni, Cu, and Zn, whereas only benzene rings can be completely decoupled in the case of MPcs with Fe and Co.

Electron Transport Suppression from Tip-π State Interaction on Si(100)-2 × 1 Surfaces

We investigate the electron transport between a scanning tunneling microscope tip and Si(100)-2 × 1 surfaces with four distinct configurations by performing calculations using density functional theory and the nonequilibrium Green's function method. Interestingly, we find that the conducting mechanism is altered when the tip-surface distance varies from large to small. At a distance larger than the critical value of 4.06 Å, the conductance is increased with a reduction in distance owing to the π state arising from the silicon dimers immediately under the tip; this in turn plays a key role in facilitating a large transmission probability. In contrast, when the tip is closer to the substrate, the conductance is substantially decreased because the π state is suppressed by the interaction with the tip, and its contribution in the tunneling channels is considerably reduced.

Produiion of a-Si1-x Cx:H powders using radiofrequency glow discharges of silane and methane mixtures

a-Si1-x Cx:H powders have been produced in radiofrequency glow discharges of SiH4 and CH4. Samples produced in discharges with different gas flow ratios (R=[CH4] / [SiH4]+[CH4], R ∼ 0.2 to 0.95) were analyzed by several techniques: Infrared spectroscopy, transmission electron microscopy and thermal desorption spectrometry of hydrogen. The microstructural properties of the a-Si1-x Cx:H powders obtained ranged between those previously reported in silicon particles and those of amorphous carbon particles. As a general rule, the particles, whose diameter ranged between 5 and 400 nm in diameter, showed an amorphous microstructure and high hydrogen content. Infrared spectroscopy showed that the hydrogen was mainly located on the particle surface and in microvoids forming CHi and/or SiHi (i=2,3) groups.

The hydrogen was removed from the powder by thermal annealing (< 700°C) under vacuum. Anlysis of the a-Si1-x Cx:H powders after this thermal treatment revealed new microstructural and optical features.

Tunable electrical properties of silicon nanowires via surface-ambient chemistry

p-Type surface conductivity is a uniquely important property of hydrogen-terminated diamond surfaces. In this work, we report similar surface-dominated electrical properties in silicon nanowires (SiNWs). Significantly, we demonstrate tunable and reversible transition of p(+)-p-i-n-n(+) conductance in nominally intrinsic SiNWs via changing surface conditions, in sharp contrast to the only p-type conduction observed on diamond surfaces. On the basis of Si band energies and the electrochemical potentials of the ambient (pH value)-determined adsorbed aqueous layer, we propose an electron-transfer-dominated surface doping model, which can satisfactorily explain both diamond and silicon surface conductivity. The totality of our observations suggests that nanomaterials can be described as a core-shell structure due to their large surface-to-volume ratio. Consequently, controlling the surface or shell in the core-shell model represents a universal way to tune the properties of nanostructures, such as via surface-transfer doping, and is crucial for the development of nanostructure-based devices.

Effects of exogenous spermidine on subcellular distribution and chemical forms of cadmium in Typha latifolia L. under cadmium stress

The effects of foliar spraying with spermidine (Spd) on the subcellular distribution and chemical speciation of Cd in Typha latifolia L. in hydroponic system were investigated. Increased Cd concentration in the medium caused an increase of Cd concentration in all tissues and all subcellular fractions, with the highest Cd level occurring in roots, followed by rhizomes and leaves and the greatest accumulation was in cell walls, soluble fraction and organelle containing fractions ranked next, respectively. The greatest amount of Cd was found in the extraction of 1 mol.L(-1) NaCl, followed by 2% HAC, deionized water, 80% ethanol, residues and the least in 0.6 mol.L(-1) HCl. The subcellular distribution and different chemical forms of Cd both decreased after Spd application and were more inhibited by 0.25 than 0.50 mmol.L(-1) Spd, especially in roots at 0.10 mmol.L(-1) Cd treatment. It could be suggested that the retention of Cd in roots, cell walls binding with metal, metal ion compartmentation in vacuoles and Cd forms existing in undissolved and integrated with pectates and protein play an important role in Cd detoxification and Spd could enhance the tolerance of cattail to Cd stress.

Unique electronic band structures of hydrogen-terminated [Formula: see text] silicon nanowires

Band structure mutation from an indirect to a direct gap is a well-known character of small hydrogen-terminated [Formula: see text] and [Formula: see text] silicon nanowires (SiNWs), and suggests the possible emission of silicon. In contrast, we show that hydrogen-terminated [Formula: see text] SiNWs consistently present indirect band gaps even at an extremely small size, according to our calculations using density functional theory. Interestingly, the band gap of [Formula: see text] SiNWs shows a quasi-direct feature as the wire size increases, suggesting the possibility of using medium SiNWs in optoelectronic devices. This result also indicates that the electronic structures of SiNWs are strongly orientation dependent.

Signature of nanodiamond in Raman spectra: a density functional theoretical study

Nanocrystalline diamond (NCD) has attracted great attention both experimentally and theoretically in the past few years. The identification of the presence and the amount of NCD in amorphous carbon film has been a challenging issue. Although Raman spectroscopy has become a standard tool for the characterization of various carbon phases, a simple criterion for identifying NCD has not yet been well-established. In the present work, a theoretical study of the Raman spectra of the model compounds of NCD is presented on the basis of the density functional calculations. The reliability of the computational approach has been tested by comparing the predicated Raman spectra of several reference molecules to those obtained experimentally. To show the unique Raman spectrum of a NCD phase, a series of the model compounds of various carbon materials including tetrahedral and hexagonal clusters, and trans-polyacetylene fragments, were considered, and subsequently their Raman spectra below 2000 cm(-1) were calculated and compared with each other. The calculated results indicate that the relatively stronger broad peak at about 480 cm(-1) could be used as the signature of a NCD phase in the sample.

Possible Gas-Phase Reactions of H2/CH4/Tetramethylsilane in Diamond/β-SiC Nanocomposite Film Deposition: An Ab-Initio Study

The Si-C bond breakings in tetramethylsilane (TMS) when interacting with H/H2 and the successive H abstractions from SiH4/CH4 in the gas mixture of H2/ CH4/TMS were studied at the CCSD(T)/6-311+G**//MP2/6-31+G** level of theory. Their rate constants between 1500 and 2500 K were estimated using a conventional transition state theory. The results indicate that (i) it is mainly the H radical that causes the Si-C bond breaking in TMS, and (ii) the successive H abstractions from SiH4 are much easier and faster than those from CH4. At low temperatures the differences of rate constants among the four types of the reactions are large, but generally reduced at high temperatures. The reaction rates show no selectivity over the pressure as verified at P = 0.00025, 0.025, 1, and 100 atm, respectively. Our results could provide the following microscopic level understanding of reactions in the synthesis of diamond/beta-SiC nanocomposite films. Although the Si content is smaller than that of C in the precursor gases, the gas mixture activated by microwave plasma technique could provide Si sources with a higher rate. The produced Si sources with excellent rigidity in sp3 hybridization competitively occupy the space on the substrate together with C sources, resulting in the deposition of diamond/beta-SiC nanocomposite films.

Computation of large systems with an economic basis set: Structures and reactivity indices of nucleic acid base pairs from density functional theory

We show here that an economic basis set can describe nucleic acid base pairs involving the hydrogen bond interactions in density functional calculations. The economic basis set in which the polarization function is added only to oxygen and nitrogen atoms of strong electronegativity can predict reliable geometric structures and dipole moment of nucleic acid base pairs, comparable to those obtained from the basis set of 6-31G* in B3LYP calculations. Combining single point calculations with the standard basis set on the geometric structures optimized by the economic basis set, the present approach has predicted accurate natural bond orbital charge, binding energy, electronegativity, hardness, softness, and electrophilicity index. The principle for basis selection presented in this study can be regarded as a general guideline in the computation of large biological systems with considerably high accuracy and low computational expense.

Density functional theory study of geometrical structures and electronic properties of silica nanowires

Silica nanowires are expected to possess structural diversity like bulk silica. We modeled three silica nanowires based on the side-shared two-membered rings, spiro-united two-membered rings, and three-membered rings, respectively. By performing density functional theory calculations, we studied their geometrical structures and electronic properties with and without the presence of external electric field. It is found that the stability of silica nanowires increases with length and diameter. As indicated by calculated large HOMO-LUMO gaps, silica nanowires are expected to be good insulating materials. The energy gaps, however, gradually decrease with applied electronic field and finally close, resulting in the breakdown of the insulating nanowires. Moreover, it is shown that the breakdown threshold remarkably increases with the nanowire diameter. These significant findings from the present calculations for the simplest silica nanowires will provide relevant insight into the structures and properties of much more complicated real silica nanowires.

Dimensionality Dependence of Optical Properties and Quantum Confinement Effects of Hydrogenated Silicon Nanostructures

The excited state properties of linear, planar, and spherical hydrogenated silicon nanostructures are studied systematically with use of a time-dependent Hartree-Fock (TDHF) approach with a semiempirical Hamiltonian. The calculated optical gaps decrease significantly from linear, planar, to spherical silicon structures, showing that the optical gap is dimensionality dependent and hence it can be varied by solely managing the shape of the nanostructures. Remarkably, the calculated exciton sizes of the lowest dipole-allowed excited states for both silicon chains and planes are approximately 26 A, revealing that the quantum confinement effect should be significantly enhanced when the sizes of silicon nanostructures are smaller than this value but not dependent on the dimensionality. A similar trend is also observed for hydrogenated silicon spherical clusters.

Geometric and Excited-State Properties of 1,4-Bis(benzothiazolylvinyl)benzene Interacting with 2,2‘,2‘ ‘-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole] Studied by a Density-Functional Tight-Binding Method

The energetics and luminescent property of a guest molecule, 1,4-bis(benzothiazolylvinyl)benzene (BT), interacting with a host molecule, 2,2',2' '-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole] (TPBI), in organic light-emitting diodes are studied by performing excited-state calculations using a time-dependent density-functional tight-binding method complemented with dispersion energy. It is found that the overlap between the TPBI emission and the BT absorption spectra shows an efficient energy transfer from the host molecule to the guest molecule when they are excited. The planar BT molecule becomes distorted when it is mixed with TPBI, resulting in a blue luminescence around 475 nm. The separation of the TPBI + BT mixture on a graphite surface is found to be energetically favorable, consistent with experimental observation.

A Family of Stable Silica Fullerenes with Fully Coordinated Structures

Theoretical electronic structure techniques have become an indispensable and powerful tool for predicting molecular properties and designing new materials. The discovery of C(60) opened a challenging field in nanoscale materials science, and since then people have been looking for its inorganic analogues. On the basis of the B3LYP/6-31G(d) calculations, here we provide theoretical evidence for a family of stable silica fullerenes with fully coordinated structures, which exhibit highly structural and energetic stabilities, very large energy gaps, and extremely good resistibilities to breakdown of the insulating capability in an applied electric field. Our calculations indicate that the discrete silica fullerenes are a possible polymorph of silica and can be synthesized under some conditions. They are expected to find novel applications in silica-based molecular devices. The present results may provide an aid in the experimental design for controllably producing desired silica clusters.

Silica Nanoarchitectures with Tailored Pores Based on the Hybrid Three- and Four-Membered Rings

Inspired by the recent developments in the controlled synthesis of porous materials, we present herein the structural prediction of silica nanoarchitectures by using the three- (3MRs) and four-membered rings (4MRs), which are more frequently found in the nanometer-sized particles than in the bulk form, as building blocks. The proposed models include the active molecular rings, thin nanowires, hollow nanotubes, discrete fullerene-like cages, and porous zeolite-like three-dimensional networks. Their geometrical and electronic structures and properties were studied by performing density functional calculations. These silica nanostructures were proved, using molecular dynamics simulations, to possess intrinsic structural stabilities with highly symmetrical geometries and regular nanochannels. These atomically well-defined clusters, (SiO)(n), are chemically more reactive than those proposed earlier and are energetically more favorable for n > 20 in high-level density functional calculations over the corresponding two-membered ring (2MR) chains and rings as well as the pure 3MR networks. The nanoparticles and nanodevices based on them are expected to have potential technological applications that mainly make use of their characteristic geometrical structures (nanosized pores) and novel electronic properties.

A Synthetic Route toward Well-Defined Stoichiometric Silica Fullerene and Nanotubes Based on Metastable Four-Membered Rings

On the basis of computational considerations, using metastable four-membered rings as building blocks, we propose novel synthetic routes toward well-defined stoichiometric silica nanofullerenes and nanotubes. The viability of the routes has been demonstrated by performing high-level density functional calculations, and the so-formed nanoarchitectures were proved to be energetically and structurally stable. Such nanostructures, if synthesized, are expected to have potential application in nanotechnology.