获得新生的维氏电桥振荡器

1940年,William Hewlett和DavidPackard两人将他们在车库中制作的一种产品投放市场,这种产品就是维氏电桥(Wien-Bridge)振荡器。它由一个单极点高通滤波器与一个单极点低通滤波串联而成。为了保持增益恒定不变,该振荡器电路采用一只白炽灯作指示灯来提供AGC(自动增益控制)。正如所有的白炽灯那样,这种指示灯具有非线性的电阻值。当你给这一振荡器电路通电时,冷白炽灯的电阻很小,从而产生很高的增益。随着增益的增大,温度不断升高的白炽灯的电阻也随之增大。因此,白炽灯具有AGC功能。这种振荡器电路一直使用了60多年,现在仍然在使用中。维氏电桥振荡器存在的唯一问题就是,增益小于1时,它不工作。我在一家电话公司供职时,     

High optical power electroabsorption waveguide modulator

A sampled grating distributed Bragg reflector-laser integrated with a waveguide Franz-Keldysh modulator is investigated for high optical power applications. The EAM modulation efficiency is demonstrated to asymptotically approach a limit determined by the internal differential photodetector efficiency. Linear photocurrent and 1 dB small signal AC compression point both exceed 70 mA, indicating high saturation power.     

Polymer pendant ligand chemistry, 4. Recovery of precious metal ions from strongly acidic solution with a polymer-supported o-phenylenediamine hydrochloride ligand

We report on the synthesis and reactivity of a polymer-supported o-phenylenediamine hydrochloride ligand, PS-PDHC, using macroporous 6% crosslinked polystyrene-divinylbenzene beads. The PS-PDHC ligand was found to be highly selective to AuCl₄⁻ ions in strongly acidic solutions in the presence of other precious metal ions, PdCl₄²⁻, PtCl₄²⁻, RhCl₆³⁻, and RuCl₅²⁻ (selectivity values: 2.5, Au/Pd; 7.5, Au/Pt; 7, Au/Rh; 2.2, Au/Ru) as well as other transition metal ions, Fe ³⁺, Cr³⁺, CU²⁺, Nit+, and Mn²⁺. The sorption capacity, selectivity, kinetics of removal and recovery, and solution isotherms have been determined for AuCl₄⁻ ions in competition with the above-mentioned metal ions. The relative ease of formation of the anionic complex in 0.5 M HCI, AuCl₄⁻ was thought to be the primary reason for its selective ability to bind to the PS-PDHC ligand by an anion-exchange mechanism. Therefore, the effect of the HCI concentration on the kinetics of AuCl₄⁻ ion removal from solution was also investigated to clearly show that raising the pH from 0 to 5 caused a dramatic decrease in rate. The AuCl₄⁻ ion can be recovered quantitatively from the PS-PDHC beads using a 5% thiourea solution in 0.1 M HCl, allowing the polymer-supported ligand to be reused.     

Preoperative anxiety and fear: a comparison of assessments by patients and anesthesia and surgery residents

We sought to compare self-assessment of preoperative anxiety levels and selection of worst fears by surgical patients with the assessments made by the anesthesia and surgery residents providing intraoperative care for those patients. One hundred inpatients at a Veterans Affairs hospital (Group 1) and 45 patients at a University hospital (Group 2) were asked to complete a brief questionnaire; the residents were asked to complete the same questionnaire. Group 1 results showed that median patient visual analog scale (VAS) scores were lower for anxiety about anesthesia compared to surgery (16 vs 22, P < or = 0.05). Anesthesia resident VAS scores were higher than patient or surgery resident scores. Neither type of resident was able to predict their individual patient's VAS score (Kendall's tau). The fear chosen with the greatest incidence by Group 1 patients and residents was "whether surgery would work". A significant number of residents (34%, anesthesia or surgery, P < or = 0.05) matched their patient's fear choice. Residents commonly chose fears related to their specialty (e.g., anesthesia residents chose anesthesia-related fears more often than surgery residents, 50% vs 28%, P < or = 0.001). In Group 2, residents demonstrated an improved ability to predict patient scores. For instance, both surgery and anesthesia residents were able to predict individual University patient VAS scores (P < or = 0.01). The fear chosen with the greatest frequency by Group 2 patients was "pain after the operation". Sixty percent of anesthesia residents matched their patients' fear choice (P < or = 0.001). This study indicates a variable ability of anesthesia and surgery residents to predict patient anxiety and fear which may be due, in part, to difficulty in understanding a Veterans Affairs hospital patient population.     

IEEE Standards for Communications and Networking [Guest Editorial]

This month's feature topic continues the theme of IEEE Standards for Communications and Networking with four additional articles.     

Lumen pressure within obliquely insonated absorbent solid cylindrical shells with application to Doppler flow phantoms

Flow phantoms used in medical ultrasound usually employ a plastic tube as a blood vessel mimic. These tubes often have acoustic properties differing significantly from the tissue and blood-mimicking media, which results in distortion of the acoustic pressure field within the tubes and, hence, of the Doppler flow spectra. Previous analyses of this problem have used some form of the infinite plate transmission coefficient, although at least one ray-based analysis has considered a cylindrical interface but with zero wall thickness. In this paper, we compare these approximate pressure fields with the exact solution for oblique incidence on a viscoelastic cylindrical shell at 5 MHz to find for which materials the plate approximation is valid. The shell has water both inside and outside, but it can be modified to use a different fluid inside and also to include absorption in either fluid. We find the plate approximation is reasonable for soft tubes such as the copolymer Cflex (Cole-Palmer, Niles, IL) but much less so for hard tubes such as polymethylmethacrylate (PMMA)     

The semantics of augmented constraint diagrams

Constraint diagrams are a diagrammatic notation which may be used to express logical constraints. They generalize Venn diagrams and Euler circles, and include syntax for quantification and navigation of relations. The notation was designed to complement the Unified Modelling Language in the development of software systems.Since symbols representing quantification in a diagrammatic language can be naturally ordered in multiple ways, some constraint diagrams have more than one intuitive meaning in first-order predicate logic. Any equally expressive notation which is based on Euler diagrams and conveys logical statements using explicit quantification will have to address this problem.We explicitly augment constraint diagrams with reading trees, which provides a partial ordering for the quantifiers (determining their scope as well as their relative ordering). Alternative approaches using spatial arrangements of components, or alphabetical ordering of symbols, for example, can be seen as implicit representations of a reading tree.Whether the reading tree accompanies the diagram explicitly (optimizing expressiveness) or implicitly (simplifying diagram syntax), we show how to construct unambiguous semantics for the augmented constraint diagram.