Automatic structures for subsemigroups of Baumslag–Solitar semigroups

This paper studies automatic structures for subsemigroups of Baumslag–Solitar semigroups (that is, semigroups presented by 〈x,y∣(yx ^m ,x ⁿ y)〉 where $m,n \in\mathbb {N}$ ). A geometric argument (a rarity in the field of automatic semigroups) is used to show that if m>n, all of the finitely generated subsemigroups of this semigroup are (right-) automatic. If m<n, all of its finitely generated subsemigroups are left-automatic. If m=n, there exist finitely generated subsemigroups that are not automatic. An appendix discusses the implications of these results for the theory of Malcev presentations. (A Malcev presentation is a special type of presentation for semigroups embeddable into groups.)     

Inside the D-stable matrices

Let $\text{DS}{}_{\mathrm{n}}\text{(}\text{F}\text{)}$ denote the set of n×nD-stable matrices with entries from $\text{F}\text{?}\text{C}$. A characterization of the interior of $\text{DS}{}_{\mathrm{n}}\text{(}\text{F}\text{)}$ considered as subset of the topological space $\text{F}$ⁿ², is given for the cases $\text{F}\text{=}\text{R}\text{and}\text{C}$.     

Enhanced material classification using turbulence-degraded polarimetric imagery

An enhanced material-classification algorithm using turbulence-degraded polarimetric imagery is presented. The proposed technique improves upon an existing dielectric/metal material-classification algorithm by providing a more detailed object classification. This is accomplished by redesigning the degree-of-linear-polarization priors in the blind-deconvolution algorithm to include two subclasses of metals--an aluminum group classification (includes aluminum, copper, gold, and silver) and an iron group classification (includes iron, titanium, nickel, and chromium). This new classification provides functional information about the object that is not provided by existing dielectric/metal material classifiers. A discussion of the design of these new degree-of-linear-polarization priors is provided. Experimental results of two painted metal samples are also provided to verify the algorithm's accuracy.     

Cavitation clouds created by shock scattering from bubbles during histotripsy

Histotripsy is a therapy that focuses short-duration, high-amplitude pulses of ultrasound to incite a localized cavitation cloud that mechanically breaks down tissue. To investigate the mechanism of cloud formation, high-speed photography was used to observe clouds generated during single histotripsy pulses. Pulses of 5-20 cycles duration were applied to a transparent tissue phantom by a 1-MHz spherically focused transducer. Clouds initiated from single cavitation bubbles that formed during the initial cycles of the pulse, and grew along the acoustic axis opposite the propagation direction. Based on these observations, we hypothesized that clouds form as a result of large negative pressure generated by the backscattering of shockwaves from a single bubble. The positive-pressure phase of the wave inverts upon scattering and superimposes on the incident negative-pressure phase to create this negative pressure and cavitation. The process repeats with each cycle of the incident wave, and the bubble cloud elongates toward the transducer. Finite-amplitude propagation distorts the incident wave such that the peak-positive pressure is much greater than the peak-negative pressure, which exaggerates the effect. The hypothesis was tested with two modified incident waves that maintained negative pressure but reduced the positive pressure amplitude. These waves suppressed cloud formation which supported the hypothesis.     

确保802.11无线局域网设备的可重复性测试

生产线上的802.11无线局域网设备测试与大多数其他类型通信设备的测试过程非常类似。但针对工作于802.11a,b,g标准产品的物理层测试需要特别注意IEEE规范的许多细节,特别是用于测试的各种参数。为帮助把WLAN设备的特殊测试问题归类,需要回顾测试过程,综合考虑如何以可承受的费用和可接受的时间得到所需要的结果。这里的讨论把无线模块定义为具有一个RF接口和一个至主设备接口的模块,该主设备包含控制模块工作的驱动程序软件(见图1)。典型例子包括基于PCMCIA模块,mini-PCI卡,USB卡和开始出现的加密数字卡。虽然这些模块的元件部份可…     

Force Calibration in Lateral Force Microscopy

An analysis of the contact mechanics and the forces of interaction in lateral force microscopy measurements is presented. This analysis allows for a new method of interpretation of the frictional forces, the lateral contact stiffness, and the contact shear strength. The technique was developed for the interpretation of frictional data obtained with colloidal probes, although results are presented which illustrate its ability to interpret measurements recorded with both colloidal probes and standard atomic force microscopy tips. The technique is found to compensate for the variations in the contact geometry, giving repeatable results for probes of different sizes. A critical review of other techniques which have been employed to interpret the frictional force in lateral force microscopy is also presented. Copyright 2000 Academic Press.     

Isoquinolin-1(2H)-ones and 1,6-naphthyridin-5(6H)-ones by an N-acylation-SNAr sequence

A new synthesis of 2,3-dialkyl-4-carbomethoxyisoquinolin-1(2H)-ones and 6,7-dialkyl-8-carbomethoxy-1,6-naphthyridin-5(6H)-ones is reported. The process involves treatment of a β-enaminoester with 2-fluoro-5-nitrobenzoyl chloride, 2-fluorobenzoyl chloride or 2-chloronicotinoyl chloride followed by heating in the presence of base. The conversion, which proceeds by an N-acylation-S_NAr reaction sequence, affords 50–86% yields when R¹ is n-alkyl but ≤30% yields when R¹ is α-branched.     

Micro-FTIR study of soot chemical composition-evidence of aliphatic hydrocarbons on nascent soot surfaces

Previous studies suggest that soot formed in premixed flat flames can contain a substantial amount of aliphatic compounds. Presence of these compounds may affect the kinetics of soot mass growth and oxidation in a way that is currently not understood. Using an infrared spectrometer coupled to a microscope (micro-FTIR), we examined the composition of soot sampled from a set of ethylene-argon-oxygen flames recently characterized (A. D. Abid, et al. Combust. Flame, 2008, 154, 775-788), all with an equivalence ratio Φ=2.07 but varying in maximum flame temperatures. Soot was sampled at three distances above the burner surface using a probe sampling technique and deposited on silicon nitride thin film substrates using a cascade impactor. Spectra were taken and analyses performed for samples collected on the lowest five impactor stages with the cut-off sizes of D(50)=10, 18, 32, 56 and 100 nm. The micro-FTIR spectra revealed the presence of aliphatic C–H, aromatic C–H and various oxygenated functional groups, including carbonyl (C=O), C–O–C and C–OH groups. Spectral analyses were made to examine variations of these functional groups with flame temperature, sampling position and particle size. Results indicate that increases in flame temperature leads to higher contents of non-aromatic functionalities. Functional group concentrations were found to be ordered as follows: [C=O]<[C–O]<[aliphatic C–H]. Aliphatic C–H was found to exist in significant quantities, with very little oxygenated groups present. The ratio of these chemical functionalities to aromatic C–H remains constant for particle sizes spanning 10-100 nm. The results confirm a previous experimental finding: a significant amount of aliphatic compounds is present in nascent soot formed in the flames studied, especially towards larger distances above the burner surface.     

The quality improvement process in telecommunications

Describes the quality improvement process recommended by Bellcore, and discusses the methodology developed for its implementation. The process is based on five principles: quality is conformance to valid requirements; the provider is responsible for quality and must demonstrate conformance; the way to achieve quality is prevention rather than inspection; the performance standard is defect-free work; and a major measurement of quality improvement is a reduction in the cost of quality. Steps for implementing quality are outlined. The cost of quality and its analysis are discussed. The application of the basic principles to the operation of network elements, the systems that provide services, the logistic systems, and administrative or white collar processes is examined, and the role of quality improvement is discussed for each of them