Capacitance multiplier and filter synthesizing network

A circuit using a differential amplifier multiplies the capacitance of a discrete interating capacitor by (r sub 1 + R sub 2)/R sub 2, where R sub 1 and R sub 2 are values of discrete resistor coupling an input signal e sub 1 of the amplifier inputs. The output e sub 0 of the amplifier is fed back and added to the signal coupled by the resistor R sub 2 to the amplifier through a resistor of value R sub 1. A discrete resistor R sub x may be connected in series for a lag filter, and a discrete resistor may be connected in series with the capacitor for a lead-lag filter. Voltage dividing resistors R sub a and R sub b may be included in the feedback circuit of the amplifier output e sub o to independently adjust the circuit gain e sub i/e sub o

Phase-lock loop frequency control and the dropout problem

Technique automatically sets the frequency of narrow band phase-lock loops within automatic lock-in-range. It presets a phase-lock loop to a desired center frequency with a closed loop electronic frequency discriminator and holds the phase-lock loop to that center frequency until lock is achieved

Improved capacitance multiplier circuit

Circuit multiplies capacitance without increasing overall circuit gain. In addition, circuit may be designed to include lag or lead/lag transfer function and independent gain adjustment

Increasing Study Abroad Participation Among Historically Excluded Students

Higher education has yet to address the deeper causes of inequities in student participation rates in study abroad programs across student demographics. Factors contributing to inequities include disparities in access to social and cultural capital and neglect of identity-related experiences of racially minoritized and first-generation, historically excluded students. This qualitative study examined faculty and staff experiences in the development of study abroad programs and explored their considerations for the needs of historically excluded students. A consensus among interview participants indicated a significant role for intentionality throughout the processes of program development, recruitment outreach, and preparation of students for the study abroad experience

The role of intermolecular coupling in the photophysics of disordered organic semiconductors: Aggregate emission in regioregular polythiophene

We address the role of excitonic coulping on the nature of photoexcitations in the conjugated polymer regioregular poly(3-hexylthiophene). By means of temperature-dependent absorption and photoluminescence spectroscopy, we show that optical emission is overwhelmingly dominated by weakly coupled H-aggregates. The relative absorbance of the 0-0 and 0-1 vibronic peaks provides a powerfully simple means to extract the magnitude of the intermolecular coupling energy, approximately 5 and 30 meV for films spun from isodurene and chloroform solutions respectively.Comment: 10 pages, 4 figures, published in Phys. Rev. Let

Using an Ultrasonic Instrument to Size Extravascular Bubbles

In an ongoing development project, microscopic bubbles in extravascular tissue in a human body will be detected by use of an enhanced version of the apparatus described in Ultrasonic Bubble- Sizing Instrument (MSC-22980), NASA Tech Briefs, Vol. 24, No. 10 (October 2000), page 62. To recapitulate: The physical basis of the instrument is the use of ultrasound to excite and measure the resonant behavior (oscillatory expansion and contraction) of bubbles. The resonant behavior is a function of the bubble diameter; the instrument exploits the diameter dependence of the resonance frequency and the general nonlinearity of the ultrasonic response of bubbles to detect bubbles and potentially measure their diameters. In the cited prior article, the application given most prominent mention was the measurement of gaseous emboli (essentially, gas bubbles in blood vessels) that cause decompression sickness and complications associated with cardiopulmonary surgery. According to the present proposal, the instrument capabilities would be extended to measure extravascular bubbles with diameters in the approximate range of 1 to 30 m. The proposed use of the instrument could contribute further to the understanding and prevention of decompression sickness: There is evidence that suggests that prebreathing oxygen greatly reduces the risk of decompression sickness by reducing the number of microscopic extravascular bubbles. By using the ultrasonic bubble-sizing instrument to detect and/or measure the sizes of such bubbles, it might be possible to predict the risk of decompression sickness. The instrument also has potential as a tool to guide the oxygen-prebreathing schedules of astronauts; high-altitude aviators; individuals who undertake high-altitude, low-opening (HALO) parachute jumps; and others at risk of decompression sickness. For example, an individual at serious risk of decompression sickness because of high concentrations of extravascular microscopic bubbles could be given a warning to continue to prebreathe oxygen until it was safe to decompress

Compressible flow structures interaction with a two-dimensional ejector: a cold-flow study

An experimental study has been conducted to examine the interaction of compressible flow structures such as shocks and vortices with a two-dimensional ejector geometry using a shock-tube facility. Three diaphragm pressure ratios ofP4 =P1 = 4, 8, and 12 have been employed, whereP4 is the driver gas pressure andP1 is the pressure within the driven compartment of the shock tube. These lead to incident shock Mach numbers of Ms = 1:34, 1.54, and 1.66, respectively. The length of the driver section of the shock tube was 700 mm. Air was used for both the driver and driven gases. High-speed shadowgraphy was employed to visualize the induced flowfield. Pressure measurements were taken at different locations along the test section to study theflow quantitatively. The induced flow is unsteady and dependent on the degree of compressibility of the initial shock wave generated by the rupture of the diaphragm