铬鞣的新视角

从碱式硫酸铬溶液的耐碱性能出发,逐步阐述了铬粉的种类与质量,碱化剂的种类与质量以及应用的方法对生产高质量蓝革的重要性。另外,简短回顾了鞣制技术对于蓝革质量的影响。     

A scheme for generating electricity using gravitational energy

A practical scheme for generating electricity using gravitational energy is presented. The scheme uses a set of massive underground spinning wheels, each wheel being fitted with a mechanism to receive and transmit gravitational torque pulses from a passing vehicle to keep the wheels in motion. Each wheel in combination with an appropriate gear system then acts as the prime mover of an alternator which produces the electricity. Design formulae relating to the power gain and the overall efficiency of the energy system are then developed. The numerical results presented in the paper indicate that a power gain of as high as 10 and an associated efficiency of conversion close to 92% can be easily achieved with a reasonable design of the system.     

Effect of Shallowness on Sediment Deposition in Recirculation Zones

Various hydrodynamic and sediment deposition experiments were conducted on a purpose-built, wide, shallow water table using a range of incoming flow and bed roughness conditions, including five flow rates, different inflow sediment concentrations, and different artificial roughness coefficients generated by four transverse string intervals. A recirculation zone was created behind a 0.5-m-wide backward-facing step on the left side of the table. Surface velocities, sediment concentrations, and processes and features of sediment deposition in recirculation zones were measured. Experimental results indicate that (1)?as the value of the shallow stability parameter increased from 0.033 to 0.47, the length of the recirculation zone decreased to less than half, but the corresponding area and volume of sediment deposition increased about four times, and (2)?it is the strength of the mixing layer rather than the size of the recirculation zone that dominates the process of sediment deposition as well as the final deposition feature.     

Nickeliferous pyrrhotite - “Waste or resource?”

Currently nickel producers are keeping a close eye on both the economic and production developments taking place at the Talvivaara open pit mines and their bio-heap-leach operations located in Finland. The concept of open pit mining combined with heap leaching is a popular concept in the copper industry and practiced on oxidised copper ore bodies with less than 1% Cu. In general, this process consumes large quantities of sulphuric acid when based on oxide mineralogy. Talvivaara is processing very low-grade, but complex Ni, Zn, Cu sulphide ore (0.27% Ni, 0.57% Zn and 0.14% Cu). Its full contained metal value at 70% base metal recovery is estimated at 40-50 USD/MT ore using long-term metal prices (all elements). Low-grade complex disseminated nickel sulphide ore bodies are fairly abundant worldwide, but in general not yet economically treatable through the conventional mine-mill-smelter route.In the Sudbury basin of Ontario there is a vast resource of ∼0.8% Ni-bearing pyrrhotite tailings, which has been disposed of separately in shallow lakes since the early 1990s in compliance with known environmental and sustainable development standards. The estimated full contained metal value at 70% nickel recovery from pyrrhotite is estimated at 90-100 USD/MT using the same long-term metal prices as for Talvivaara. Supply of sulphuric acid is abundant from nickel smelter operations in the basin. There are, in addition, many other low-grade ore bodies where nickel-bearing pyrrhotite, with or without pentlandite exsolution flames, is readily available. This commercial context raises the question whether Ni-bearing pyrrhotite can be considered a sustainable resource.In this paper some historical context behind pyrrhotite processing in the Sudbury area is provided. Flow sheet design considerations based on both technical and economic factors are reviewed with the objective of providing the nickel industry with tools for informed decision-making on the possibilities for exploitation of this low-grade nickel sulphide raw material.     

Low frequency dispersion in GaSe thin films

Frequency domain measurements on GaSe thin films have been carried out in the frequency range 10⁻² to 10⁴ Hz and temperature range 300 to 480 K. The measured samples with different contacts have shown low frequency dispersion (LFD) with activation energies 0.66±0.03 eV, 0.72±0.03 eV and 0.65±0.03 eV, respectively. Complex capacitance C(ω) behaviour of GaSe thin film with different contacts suggests possible contribution of diffused contact material.     

Sonar-based mobile robot navigation through supervised learning on a neural net

For mobile robot navigation in an unknown and changing environment, a reactive approach is both simple to implement and fast in response. A neural net can be trained to exhibit such a behaviour. The advantage is that, it relates the desired motion directly to the sensor inputs, obviating the need of modeling and planning. In this work, a feedforward neural net is trained to output reactive motion in response to ultrasonic range inputs, with data generated artificially on the computer screen. We develop input and output representations appropriate to this problem.A purely reactive robot, being totally insensitive to context, often gets trapped in oscillations in front of a wide object. To overcome this problem, we introduce a notion of memory into the net by including context units at the input layer. We describe the mode of training for such a net and present simulated runs of a point robot under the guidance of the trained net in various situations. We also train a neural net for the navigation of a mobile robot with a finite turning radius. The results of the numerous test runs of the mobile robot under the control of the trained neural net in simulation as well as in experiments carried out in the laboratory, are reported in this paper.     

Biological and chemical factors affecting the valuations of north-east indian plains teas: I.—Statistical association of liquor characteristics with cash valuations of black teas

An attempt has been made, by using the multiple regression technique, to determine whether the term ‘quality’ of the North-East Indian plains black teas has its own single characteristic as recognisable by tea- tasters or if it is the integration of some of the other important liquor characteristics, viz., colour, strength, brightness and briskness, and to determine the influence of those liquor characteristics including quality on the ‘cash valuations’ of black teas. The multiple regression analyses showed that in general, regardless of tasters and methods of manufacture, quality of North-East Indian plains black tea was found to depend mainly on briskness, quality being increased with an increase in briskness. Cash valuations, both of crushing, tearing and curling (C.T.C.) and orthodox manufactured teas, in general, depended mainly on quality and/or briskness, cash valuation being increased with increase in quality and/or briskness.     

Carbon nanotube arrays for optical design of amorphous silicon solar cells

Effective light trapping is essential for the conversion efficiency increase in thin film solar cells. Vertically aligned multiwalled carbon nanotubes (MWNTs) arrays with proper spacing form an ideal light trapping structure. In this work, we have demonstrated feasibility of the incorporation of MWNTs as back contact into amorphous silicon solar cells. Intrinsic amorphous silicon films were uniformly deposited onto vertically aligned MWNTs arrays. Scanning Electron Microscopy (SEM) was used to investigate the surface morphology of our films. The film surface area exposed to light was found to be increased dramatically due to the high-aspect ratio of MWNTs. Our findings open up a new way of managing light in thin film silicon solar cells by controlling the nano-geometry of MWNTs on substrates.     

Enhanced emission from single component organic core-shell nanoparticles

By one-step mixed-solvent mediated approach, we have prepared fluorescent organic core-shell nanoparticles with an oligomer (1) derived from the Schiff base condensation reaction of 2,6-diformyl-4-methylphenol and o-phenylenediamine at room temperature. The core and shell structures are generated by the same oligomer (1) featuring the aggregation structure in core different from that in shell. The radial packing factor distribution of oligomer cluster depending on the solvent interaction in the time of nucleation is mainly responsible for the single component core-shell formation. Different morphologies of the core-shell nanospheres (CSNS) and core-shell nanohemispheres (CSNHS) were generated simply by changing the concentration of 1 in chloroform-methanol mixed solvent (1:2). We observed that fluorescent emission from those core-shell nanoparticles is intense whereas as-synthesized oligomer (1) itself is non-fluorescent in dilute solution. The enhanced emission in the core-shell form with more than 50 times increase in fluorescent quantum yield vis-à-vis 1 is a remarkable feature of the study. As UV absorption spectra of nanoparticles are blue-shifted relative to their properties in solution, the observed strong emission in the solid state makes the oligomer an outstanding exception to a well-established rule based on the molecular exciton model. The core-shell nanoparticles have been characterized by FE-SEM, TEM, XRD, nanosecond (ns) time-resolved fluorescence dynamics, UV-Vis and fluorescence spectroscopy. The longer fluorescence lifetimes (tau) of core-shell nanoparticles (3.50 ns and 3.52 ns for CSNS and CSNHS respectively) than 1 as-synthesized (1.28 ns) implies that the formation of the nanoparticles restricts the rotation and vibration of the groups in the molecules. The factor that induces fluorescent enhancement of nanoparticles is mainly ascribed to the increase of radiative rate constant (k(r)) and simultaneous decrease of nonradiative rate constant (k(nr)).