Effectiveness of crossflow plate heat exchanger for indirect evaporative cooling: Efficacité des échangeurs thermiques à plaques, à courants croises pour refroidissement indirect évaporatif

A short-cut method for calculating the effectiveness of wet surface crossflow plate heat exchangers is developed. It introduces a correction for the effectiveness estimated according to the method of Maclaine-cross and Banks. For this purpose a new model with a water film that flows down, corresponding to the real conditions in these heat exchangers, is developed. The method of Maclaine-cross and Banks is improved by an approach to determine the mean water surface temperature and by derivation of an equation for calculating the ratio of total to sensible heat taking into account the barometric pressure. Performance predictions by this method for wet surface crossflow plate heat exchangers are found to agree with the finite difference solutions.     

Synthesis and structure of glasses in the system BaO-MnO-SiO2

Glasses corresponding in composition to BaMnSiO₄ and BaMnSi₂O₆ crystalline phases synthesized previously, have been obtained in the region with low SiO₂ content of the BaO-MnO-SiO₂ system. The glass structures were investigated by electron spin resonance, ultraviolet-visible and infrared spectroscopy, X-ray diffraction methods, etc. The trend to a complex ortho-silicate structure owing to the transformations into diortho-groups and silicate rings, has been established. The R ₁ (0.186–0.177 nm) maxima of the total pair correlation functions are related to the mean Si-O and Mn-O distances, while the R ₂ (0.283–0.278 nm) maxima refer to the Ba-O distance. Conclusions are drawn concerning the formation of Mn-O and Ba-O polyhedra. It is assumed that several kinds of structural polyhedra participate in the formation of the glass network.     

Charge Transfer Modulation in Vanadium-Doped WS2/Bi2O2Se Heterostructures

The field of photovoltaics is revolutionized in recent years by the development of two–dimensional (2D) type-II heterostructures. These heterostructures are made up of two different materials with different electronic properties, which allows for the capture of a broader spectrum of solar energy than traditional photovoltaic devices. In this study, the potential of vanadium (V)-doped WS₂ is investigated, hereafter labeled V-WS₂, in combination with air-stable Bi₂O₂Se for use in high-performance photovoltaic devices. Various techniques are used to confirm the charge transfer of these heterostructures, including photoluminescence (PL) and Raman spectroscopy, along with Kelvin probe force microscopy (KPFM). The results show that the PL is quenched by 40%, 95%, and 97% for WS₂/Bi₂O₂Se, 0.4 at.% V-WS₂/Bi₂O₂Se, and 2 at.% V-WS₂/Bi₂O₂Se, respectively, indicating a superior charge transfer in V-WS₂/Bi₂O₂Se compared to pristine WS₂/Bi₂O₂Se. The exciton binding energies for WS₂/Bi₂O₂Se, 0.4 at.% V-WS₂/Bi₂O₂Se and 2 at.% V-WS₂/Bi₂O₂Se heterostructures are estimated to be ≈130, 100, and 80 meV, respectively, which is much lower than that for monolayer WS₂. These findings confirm that by incorporating V-doped WS₂, charge transfer in WS₂/Bi₂O₂Se heterostructures can be tuned, providing a novel light-harvesting technique for the development of the next generation of photovoltaic devices based on V-doped transition metal dichalcogenides (TMDCs)/Bi₂O₂Se.     

Electrochemical method for quantitative determination of trace amounts of lead

An ultrasensitive chronoamperometric method for quantitative determination of trace amounts of lead (down to 20 ppb) in acidic solutions is proposed in this paper. The method is based on observations that a complete underpotentially deposited (UPD) lead layer inhibits the electroreduction of nitrate on a bare Cu(111) electrode. To asses the limits of the method, both the electroreduction of nitrate and UPD of lead monolayer on copper single (111) and polycrystalline electrodes in perchloric acidic solution are studied by means of cyclic voltammetry, chronoamperometry, and rotating disk electrode (RDE) experiments. It is found that an inexpensive polycrystalline copper electrode is sensitive enough for analytical detection of lead traces in electrolytes down to 1 x 10(-8) M. Analytical results obtained by the proposed method in 2 orders of magnitude concentration range are compared to atomic absorption spectroscopy measurements to evaluate and assess the sensitivity of the employed experimental protocol. The excellent match between both analytical approaches validates the applicability of the proposed method.     

An Investigation of the Capability Profile of the Three Dimensional Printing Process with an Emphasis on the Achievable Accuracy

A benchmark procedure has been designed to assess the dimensional as well as the geometric accuracy of currently one of the most widely used rapid prototyping processes - the Three Dimensional Printing. It tests not only linear accuracy but also precision, and repeatability of the process, as well as its ability to create manufacturing features such as fillets and draft angles. The presented research results reflect the necessity to adequately respond to engineering requirements for clearly meeting dimensional and geometric tolerances and root on several in-house case studies proving the comparison with established high-end RP processes.     

AlN nanoclusters formation by plasma ion immersion implantation

We report on simultaneous (Al + N) implantation of Al and N into layers of amorphous thermal silica (SiO₂) in an attempt to bond Al with N and form the binary compound AlN. As an implantation technique, plasma ion immersion implantation (PIII) is used. The energy and ion fluence were varied in order to obtain nanocluster containing films in the thickness range 10-50 nm. The elemental distribution profiles in the substrate were evaluated by means of elastic recoil detection analysis technique (ERDA). The nature of the chemical bonds was determined by X-ray photoelectron spectroscopy (XPS). The simultaneous implantation using rf plasma source for N ions and a cathodic arc to produce the Al ions provides good overlap of the elemental profiles and high retained doses of Al and N are achieved. The binding energies of the Al 2p and N 1s core electrons indicate that formation of near-stoichiometric aluminium nitride is achieved.     

Influence of plating parameters and solution chemistry on the voiding propensity at electroplated copper–solder interface

Interfacial voiding in solder joints formed with Sn–Ag–Cu solder alloys and electroplated Cu was examined as a function of the plating solution chemistry and parameters. Galvanostatic Cu plating of ~10 μm thick Cu films was performed in a commercially available plating solution, and in model generic plating solutions. Analysis of the current voltage behavior along with Secondary Ion Mass Spectrometry studies of organic impurity content of two plated and a wrought copper samples, yielded a conclusion that for certain chemistry solutions (e.g., H₂SO₄ + CuSO₄ + Cl^? + PEG) and current density ranges above 2.5 mA cm^?2, organic impurities were incorporated into the growing Cu. Solder joints were produced with a variety of electroplated Cu samples. These joints were, then, annealed at a temperature of 175 °C for 1 week, cross sectioned and examined. In general, it was observed that interfacial voiding in laboratory electroplated Cu layers was qualitatively similar to the unexplained voiding observed in some industrially plated Cu products. More specifically, it was found that the propensity for voiding could be correlated with specific electroplating parameters that in turn were associated with significant incorporation of organic impurities in the Cu deposit.     

3-D Silicon Hall sensor for use in magnetic-based navigation systems for endovascular interventions

This paper presents the design of a new 3-D Hall sensor compatible with standard silicon IC technology and optimization of its characteristics through originally realized amperometric scheme. This magnetic Hall effect sensor is intended to be fitted at the tip of a catheter for use in a magnetic-based navigation system for endovascular interventions. Unfortunately, at present the general feeling is that vector Hall sensors cannot be used for clinical trials, mainly because of their large size and low sensitivity. Proposed 3-D silicon Hall sensor has denied suspicions with its advantages: simultaneous on line 3-D measurement of the magnetic field components; high spatial resolution 150 μm × 150 μm × 100 μm; the lowest detected magnetic induction of the three output channels is about 15/20 μT; magnetosensitivities of the three channels at a supply current 10 mA reach 360 μA/T for B_x and B_y, 250 μA/T for B_z, respectively.