Enhanced field electron emission properties of hierarchically structured MWCNT-based cold cathodes

Hierarchically structured MWCNT (h-MWCNT)-based cold cathodes were successfully achieved by means of a relatively simple and highly effective approach consisting of the appropriate combination of KOH-based pyramidal texturing of Si (100) substrates and PECVD growth of vertically aligned MWCNTs. By controlling the aspect ratio (AR) of the Si pyramids, we were able to tune the field electron emission (FEE) properties of the h-MWCNT cathodes. Indeed, when the AR is increased from 0 (flat Si) to 0.6, not only the emitted current density was found to increase exponentially, but more importantly its associated threshold field (TF) was reduced from 3.52 V/μm to reach a value as low as 1.95 V/μm. The analysis of the J-E emission curves in the light of the conventional Fowler-Nordheim model revealed the existence of two distinct low-field (LF) and high-field (HF) FEE regimes. In both regimes, the hierarchical structuring was found to increase significantly the associated β_LF and β_HF field enhancement factors of the h-MWCNT cathodes (by a factor of 1.7 and 2.2, respectively). Pyramidal texturing of the cathodes is believed to favor vacuum space charge effects, which could be invoked to account for the significant enhancement of the FEE, particularly in the HF regime where a β_HF as high as 6,980 was obtained for the highest AR value of 0.6.     

CVD growth and field electron emission of aligned carbon nanotubes on oxidized Inconel plates without addition of catalyst

Direct growth of carbon nanotubes (CNTs) on Inconel 600 sheets was investigated using plasma enhanced hot filament chemical vapor deposition in a gas mixture of methane and hydrogen. The Inconel 600 sheets were oxidized at different temperatures (800 °C, 900 °C, 1000 °C, and 1100 °C) before CNT deposition. The structure and surface morphology of the pre-treated substrate sheets and the deposited CNTs were studied by scanning electron microscopy (SEM) and X-ray diffraction. The field electron emission (FEE) properties of the CNTs were also tested. The SEM results show that well aligned CNTs have been grown on the pre-treated Inconel sheets without addition of any catalysts and the higher treatment temperature resulted in CNTs with better uniformity, indicating that the oxidation pre-treatment of the substrate is effective to enhance the CNT growth. FEE testing shows that CNTs with better height uniformity exhibit better FEE characteristics.     

Nd^3＋：L-Lys：thiourea：TGS晶体的生长与性能研究

利用水溶液降温法生长了掺杂稀土离子Nd^3＋、L-赖氨酸和硫脲的TGS晶体。测试了掺杂TGS晶体的晶胞参数和热释电性能。实验表明,三掺杂的TGS晶体的热释电系数、热释电优值比和内偏压场大于纯TGS。     

Sensitivity of SnO2 semiconductor gas sensors to CO in the presence of high concentrations of water vapour

Amongst future uses of semiconductor gas sensors, one important application could be the measurement of emission gases for the control of combustion processes. In such measurements, water vapour is always present as a factor that can cause interference. Combustion gases, depending on the fuel, can contain up to 20% by volume of water vapour. Therefore, it is important to elucidate the influence exercised by water vapour on the sensor. In this study, the sensitivities of SnO₂-based gas sensors to CO and water vapour were investigated in the laboratory. The concentration of water vapour was varied in the range of 0 to 19·9% by volume. The sensors tested were thick film sensors prepared in the laboratory as well as commercial TGS 812 sensors. Water vapour and CO were found to have a synergistic effect on the conductance of TGS sensor but not on the conductance of the thick film sensor. Due to the absence of the synergistic effect between CO and water vapour the thick film sensor is much less sensitive to the variation of the concentration of water vapour in the range of a few percent to 20% by volume than the TGS 812 sensor.     

Specific heat and quadrupole interactions in uniaxial ferroelectrics

The inclusion of quadrupolar and higher order terms into the effective field in second order transition in uniaxial ferroelectrics is shown to describe well the jump in specific heat at T⋍T_c for crystals of the TGS family. It is shown that the numerical values for the coefficient g≡(γ/β)(Nμ)², corresponding to the quadrupolar interaction term, obtained (a) from specific heat data and (b) from spontaneous polarization data (both at T⋍T_c are in good agreement with each other for crystals of the TGS family.     

Bacterial Cellulose Membrane Containing Epilobium angustifolium L. Extract as a Promising Material for the Topical Delivery of Antioxidants to the Skin

Bacterial cellulose membranes (BCs) are becoming useful as a drug delivery system to the skin. However, there are very few reports on their application of plant substances to the skin. Komagataeibacter xylinus was used for the production of bacterial cellulose (BC). The BC containing 5% and 10% ethanolic extract of Epilobium angustifolium (FEE) (BC-5%FEE and BC-10%FEE, respectively) were prepared. Their mechanical, structural, and antioxidant properties, as well as phenolic acid content, were evaluated. The bioavailability of BC-FESs using mouse L929 fibroblasts as model cells was tested. Moreover, In Vitro penetration through the pigskin of the selected phenolic acids contained in FEE and their accumulation in the skin after topical application of BC-FEEs was examined. The BC-FEEs were characterized by antioxidant activity. The BC-5% FEE showed relatively low toxicity to healthy mouse fibroblasts. Gallic acid (GA), chlorogenic acid (ChA), 3,4-dihydroxybenzoic acid (3,4-DHB), 4-hydroxybenzoic acid (4-HB), 3-hydroxybenzoic acid (3-HB), and caffeic acid (CA) found in FEE were also identified in the membranes. After topical application of the membranes to the pigskin penetration of some phenolic acid and other antioxidants through the skin as well as their accumulation in the skin was observed. The bacterial cellulose membrane loaded by plant extract may be an interesting solution for topical antioxidant delivery to the skin.     

Study of the relaxation of the permittivity in doped and gamma-irradiated TGS single crystals

The change of the permittivity in gamma-irradiated and chromium and vanadgl doped TGS single crystals is investigated after switching of an applied d.c. electric field. Two types of the time dependence of the permittivity are observed. This behaviour may be correlated to real domain structure.     

Effect of ultraviolet irradiation on the surface potential of Fe3 admixtured TGS crystal

Measurements of the surface potential were carried out by electrostatic induction probe method. The influence of doping with Fe3+ cations on the surface potential of TGS crystal was tested. The behaviour of surface potential was studied for TGS with Fe3+ cations under influence of ultraviolet irradiation. The dependence of surface potential on irradiation time was found. After the ultraviolet irradiation of Fe3+ admixtured TGS slower changes of surface potential than for pure TGS crystal were observed.     

Equivalence between bias and external fields in latgs crystal using the scaled relation of dielectrical susceptibility

The dielectric susceptibility Ξ of a LATGS crystal was measured at different temperatures and applied external fields E_ext. The internal bias field B is obtained and the data are compared with those in pure TGS using the scaled relation of susceptibility. The equivalence between B and E_ext is discussed.     

Non-linear dielectric properties in paraelectric phase of γ-damaged TGS crystal

The non-linear dielectric properties in the paraelectric phase of γ-irradiated TGS crystal are studied. The temperature dependence of non-linearity coefficient B is found. It is claimed that the non-linearity depends on orientation of effective field with regard to bias field. It is also shown that the time dependence of ε at dc field as well as the observed hysteresis of ε(E) dependence can be explained assuming existence of the bias soft component.     

Well behaved temperature dependence of the ferroelectric coercive field near Tc in TGS

A new and simple method is introduced to make experimental observations of the coercive field of a ferroelectric which avoids the ambiguities associated with the amplitude dependence of this quantity. The temperature dependence of the coercive field of TGS in the vecinity of T_c has been measured and found to obey a law E_c = A(T_c - T)^s, with s = 1.45±0.10, in good agreement with the theoretical prediction s = 3/2.     

Finding the global minimum: a fuzzy end elimination implementation

The ‘fuzzy end elimination theorem’ (FEE) is a mathematicallyproven theorem that identifies rotameric states in proteinswhich are incompatible with the global minimum energy conformation.While implementing the FEE we noticed two different aspectsthat directly affected the final results at convergence. First,the identification of a single dead-ending rotameric state cantrigger a ‘domino effect’ that initiates the identificationof additional rotameric states which become dead-ending. A recursivecheck for deadending rotameric states is therefore necessaryevery time a dead-ending rotameric state is identified. It isshown that, if the recursive check is omitted, it is possibleto miss the identification of some dead-ending rotameric statescausing a premature termination of the elimination process.Second, we examined the effects of removing dead-ending rotamericstates from further considerations at different moments of time.Two different methods of rotameric state removal were examinedfor an order dependence. In one case, each rotamer found tobe incompatible with the global minimum energy conformationwas removed immediately following its identification. In theother, dead-ending rotamers were marked for deletion but retainedduring the search, so that they influenced the evaluation ofother rotameric states. When the search was completed, all markedrotamers were removed simultaneously. In addition, to expandfurther the usefulness of the FEE, a novel method is presentedthat allows for further reduction in the remaining set of conformationsat the FEE convergence. In this method, called a tree-basedsearch, each dead-ending pair of rotamers which does not leadto the direct removal of either rotameric state is used to reducesignificantly the number of remaining conformations. In thefuture this method can also be expanded to triplet and quadrupletsets of rotameric states. We tested our implementation of theFEE by exhaustively searching ten protein segments and foundthat the FEE identified the global minimum every time. For eachsegment, the global minimum was exhaustively searched in twodifferent environments: (i) the segments were extracted fromthe protein and exhaustively searched in the absence of thesurrounding residues; (ii) the segments were exhaustively searchedin the presence of the remaining residues fixed at crystal structureconformations. We also evaluated the performance of the methodfor accurately predicting side chain conformations. We examinedthe influence of factors such as type and accuracy of backbonetemplate used, and the restrictions imposed by the choice ofpotential function, parameterization and rotamer database. Conclusionsare drawn on these results and future prospects are given     

稀土和双有机取代基TGS晶体生长和性能研究

选择稀土离子Ce3＋、Nd3＋、Eu3＋作为掺杂阳离子,采用水溶液降温法生长了7种双有机取代基TGS晶体。研究了其晶胞参数、主要的热释电和铁电性能参数。发现这几种掺杂TGS晶体的品质因子有了提高。     

Pyroelectric properties of valine doped TGS single crystals

TGS was grown by a slow cooling technique adding several kinds of dopants (10 and 20 mole% alanine, 10% alanine + LiVO₃, 10% and 20% valine) to an aqueous solution. The temperature dependent pyroelectric coefficient, p and the spontaneous polarization, P_s, of doped-TGS crystals were measured to study the transition temperature, P_max and room temperature pyroelectric coefficient depending on the dopants and to calculate the figure of merit, (p/K), (K is a dielectric constant). Furthermore, several pieces were selected to investigate the positional inhomogeneities of the same sample. Moderate figure of merit (p/K) was obtained in valine doped TGS because of low temperature dielectric relaxation around -10°C, although valine doped TGS has a three times higher pyroelectric coefficient (p = 1.671μC/cm²K) at transition temperature (T_c) than that of alanine doped TGS.     

Chemosensory responses in two species of elephants to constituents of temporal gland secretion and musth urine

This report discusses three areas of investigation: (1) The chemical components in the temporal gland secretion (TGS) of Asian (Elephas maximus) and African (Loxodonta africana) elephants were characterized by radioimmunoassay (RIA) for testosterone (T) and dihydrotestosterone (DHT) levels and by on-column capillary column gas chromatographic analysis of volatiles. An inverse relationship between TGS testosterone levels and (E)-farnesol levels was observed. (2). African elephants responded preferentially toward a particular constituent of African elephant TGS. (3) Urine from Asian bull elephants in musth was partially fractionated by high-performance liquid chromatography. Specific chromatographic regions elicited dramatic avoidance responses from female African elephants. These results support the suggestion that the TGS plays multiple chemocommunicative roles.     

A method of experimental measures of switching current on ferroelectric samples

An experimental system, suitable for analysis of the switching current of ferroelectric materials has been developed. It can produce a great variety of excitation signals and includes an adquisition data system controlled by a microprocessor, that allows the processing of the signals and their display in a plotter or in a oscilloscope. This system is especially arranged for the study of the dependence of switching on field, delay time and temperature in TGS.     

Dielectric and pyroelectric properties of triglycine sulphate-polystyrene composites

A composite of Triglycine sulphate (TGS) and polystyrene has been fabricated by mixing different particle size TGS powders (75 μm to 400 μm) and polystyrene solution. The dielectric constant has been measured in the frequency range 0.1 to 100 KHz, and the pyroelectric current measurements were made by the Byer and Roundy direct method. Specific heat of the composite was determined by the differential them analysis (DTA) technique.

Particle size dependance of dielectric constant, pyroelectric coefficient and responsivity have been studied. Anomalies in ε' and P_y were observed even in the composite with the lowest particle size of TGS (75 μm). The surface effects have much greater influence on electrical properties but thermal properties are, not affected. This is indicated by a decrease in ε' and P^y with decreasing particle size of TGS, while specific heat of composite is almost independent of particle size.     

Electrogyration of pure and X-Irradiated TGS crystals

Dispersion of optical rotatory power δ, temperature dependence of δ and electrogyration of hysteresis loops of pure and X-irradiated TGS crystals have been measured, The relation between OA and P_s and the origin of OA in TGS crystal is discussed.     

A method for collection,long-term storage,and bioassay of labile volatile chemosignals

A procedure for headspace sampling and long-term storage of organic volatiles coupled with gas chromatographic-mass spectrometric (GC-MS) analysis was used to study the volatile chemosignals in a biological secretion prior to bioassay. The approach involved collecting the volatiles in evacuated canisters from an apparatus in which 1 ml of secretion was dispersed for headspace sampling. These canisters, stainless steel, 850 ml, and 100% internally electropolished, have been demonstrated to store volatile compounds, in chemically stable form, for several weeks. The GC-MS analyses provided the quantitation and identification of compounds from C₃ through C₁₄ at concentrations as low as 0.10 parts per billion volume. The approach was used to study chemosignals of musth temporal gland secretions (TGS) from a male Asian elephant (Elephas maximus). Fresh TGS material loses its biological activity within 1 hr. TGS material stored at –20°C usually looses its activity within 30 days. The usefulness of this method for long-term storage of the volatile chemosignals was demonstrated by the retention of biologically active TGS headspace compounds, as determined through bioassays, stored in these canisters for one year.