Laser milling of ceramic components Pham, D.T.; Dimov, S.S.; Petkov, P.V.
International journal of machine tools & manufacture,
03/2007, Letnik:
47, Številka:
3
Journal Article
Recenzirano
Conventional methods of producing ceramic components are based on sintering technology which requires expensive tooling making it uneconomic for small batch fabrication. Laser milling provides a new ...method of producing parts in a wide range of materials, including ceramics, directly from CAD data. This paper considers the technical capabilities of laser milling when applied to the machining of microcomponents from alumina and silicon nitride ceramics. The main parameters affecting the material removal characteristics of laser milling are reviewed. A new technique for machining alumina components is proposed emphasising the importance of correct set-up design in achieving a high level of accuracy. Process parameters influencing part quality are analysed and guidelines for machine set-ups are formulated. The paper concludes with an assessment of the accuracy of the laser milling process.
•Magnetically disordered phase is suppressed under pressure.•The Néel temperature increases substantially under pressure.•The mechanism of next nearest neighbor superexchange interactions of A-O-O-A ...type is proposed.
The crystal and magnetic structures of the frustrated Co3O4 spinel oxide have been studied by means of neutron diffraction at high pressures up to 8.7 GPa in the temperature range 5–300 K. At ambient pressure, a coexistence of the long range ordered antiferromagnetic (AFM) phase and short range disordered phase below TN = 33 K was observed. At pressures above 2 GPa, a suppression of the magnetically disordered phase and stabilization of the AFM phase, characterized by rapid increase of the Néel temperature in 1.5 times from 33 to 51 K with a pressure coefficient dTN/dP = 2.1 K/GPa occur. The observed phenomena are analyzed in terms of the competing nearest neighbor and next nearest neighbor magnetic interactions. In addition to the A-O-B-O-A nearest neighbor superexchange, an important role of the A-O-O-A next nearest neighbor superexchange interactions in magnetic behavior of Co3O4 is pointed out.
The paper present design of low-cost antenna array for RFID indentification in the frequency range 865 to 868 Mhz. The design antenna has enhanced coverage (pattern) and beam-steering capabilities. ...It can serve as a base element for more sophisticated RFID readers with direction finding capabilities and improved distance of tag reading.
Granular nanocrystalline Bi
2
(Se
1-x
Te
x
)
3
films were prepared from highly crystalline bulk alloys used as source materials by means of thermal evaporation under vacuum (2 × 10
−6
mbar). The ...nanofilms were deposited onto highly cleaned glass substrates of BK7 type. The structural characteristics, including surface morphology, roughness, and crystallite size, were studied by X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analysis. Perfect crystallinity and nanoscalability of the prepared samples were asserted. Transmittance and reflectance spectra of the prepared nanofilms were investigated over the wavelength range of 400-2,700 nm. In the visible light region, all of the films showed an opaque behavior; however, as the wavelength increased into the infrared region, a growing transparency was observed. Based on the measured transmission and reflection spectra, the coefficients of absorbance and extinction as well as the optical band gap were determined. The refractive index was deduced from the reflectance measurements using the determined extinction coefficient. Direct allowed band transitions were confirmed in all films with a band gap energy of 0.85-1.05 eV, depending on the Te content. The possibility of an indirect band gap in the lower photon energy region was discussed. The Seebeck coefficient and electrical conductivity were measured in the temperature range of 300-500 K. Very large values of the power factor of 80 and 131
were obtained for Be
2
Se
3
films at room temperature and 473 K, respectively; the latter is three times larger than best previously reported values for similar film systems.
A generalization of an earlier proposed method for analysis of Doppler-shift attenuation lifetime measurements, namely the Spectral difference method, is presented for the case of Recoil distance ...Doppler-shift or plunger experiments. Using the data at only one distance between the target and stopper, the lifetime is derived directly by fitting the time dependence of the population of the level of interest using the line shape of the depopulating transition and the difference of the spectra of the depopulating and feeding transitions. Practical application to real data proves the applicability of the new procedure by reproducing literature lifetime values.
Objective To assess parental attitudes regarding placebo use in pediatric randomized controlled trials and clinical care. Study design Parents with children under age 18 years living in the US ...completed and submitted an online survey between September and November 2014. Results Among all 1300 participants, 1000 (76.9%; 538 mothers and 462 fathers) met the study inclusion criteria. The majority of surveyed parents considered the use of placebos acceptable in some pediatric care situations (86%) and some pediatric trials (91.5%), whereas only 5.7% of parents found the use of placebos in children always unacceptable. The clinical use of placebo was considered acceptable by a majority of parents for only 7 (mostly psychological) of the 17 conditions presented. Respondents' judgment about acceptability was influenced by the doctors' opinions about the therapeutic benefits of placebo treatment, the conditions for pediatric placebo use, transparency, safety, and purity of placebos. Conclusion Most surveyed parents accepted the idea of using placebos in pediatric trials and within the clinic for some conditions without the practice of deception and with the creation of guidelines for ethical and safe use. This study suggests a need to reconsider pediatric trial design and clinical therapy in the light of generally positive parental support of appropriate placebo use.
Lifetime measurements of excited states in doubly-magic 56Ni have been performed exploiting the Doppler-shift attenuation method in order to determine reduced transition probabilities. For the 41+ ...and 61+ states, the deduced B(E2) values are compared with results from shell-model calculations employing the GXPF1A and the modern PFSDG-U interactions. In addition, valence ab-initio calculations were performed using a novel realistic Hamiltonian derived from chiral perturbation theory including three-body potential contributions and are confronted with the experimental findings. The new results show maximum E2 strength in comparison with known values along the N=28 chain of isotones. The results corroborate the high collectivity for the double shell closure at N=Z=28 which was anticipated from the large B(E2;21+→0g.s.+) value despite the considerable increase of its excitation energy as compared to neighboring semi-magic nuclei. Based on similarities in the shell structures of the self-conjugate doubly-magic nuclei 56Ni and 100Sn, the new values could be an indication for an expected comparable collective behavior of the 61+ state in 100Sn.
The aim of this paper is to describe in detail the
μ
-synthesis of a miniature helicopter integral attitude controller of high order and to present results from the hardware-in-the-loop simulation of ...this controller implementing Digital Signal Processor. The
μ
-controller designed allows to suppress efficiently wind disturbances in the presence of 25 % input multiplicative uncertainty. A simple position controller is added to ensure tracking of the desired trajectory in 3D space. The results from hardware-in-the-loop simulation are close to the results from double-precision simulation of helicopter control system in Simulink
®
. The software platform developed allows to implement easily different sensors, servoactuators and control laws and to investigate the closed-loop system behavior in presence of different disturbances and parameter variations.
Sb2Te3-containing alloys can be employed for many applications, including in solar cells, thermoelectric devices, and phase-change devices. For the first time in the literature, Nano-powder-based ...samples of Bi-doped Sb2Te3 were used as sources to prepare the corresponding films. Such films were expected to show numerous interesting features such as solid-state operation, special scalability, low maintenance, and a long operating lifetime. The crystal structure of the synthesized powders and nano-powder films is studied and investigated in the present manuscript by means of x-ray diffraction, scanning electron microscopy and atomic force microscopy analysis. Better adhesion to the glass substrates is revealed for the films prepared in our work. High absorption in the visible region is observed, confirming potential applications in the field of recording devices. Optical studies confirmed direct and allowed transitions in both films with energy band gaps of 0.78-0.83 eV. Refractive index (n), and dielectric constants ( r) and ( i) are calculated and studied as a function of the wavelength.
The objective of this study is to determine the impact of an original fitness model, based on circuit training on the level of physical quality muscle strength of female students of Trakia ...University. The testing was conducted in the academic year 2016/2017. A contingent of the study were 69 female students of secondary age 20,04 years from the first and second year of three faculties of Trakia University - Economics, Agricultural, and Veterinary Medicine. They were divided into two groups. In an experimental group of 36 female students circuit training twice a week for 30 weeks had been conducted. A control group of 33 female students, were trained according to an approved curriculum for the discipline "Physical Sports and Education". To achieve the objective, we used the following methods: testing, pedagogical experiments, analysis of variance, comparative analysis, and graphical analysis. Their results and analysis showed that the experiment was successful and the developed fitness program is effective. The author's fitness model based on circuit workouts improved the muscular strength of female students.
PDF
