Geothermal reservoir engineering research

The Stanford University research program on the study of stimulation and reservoir engineering of geothermal resources commenced as an interdisciplinary program in September, 1972. The broad objectives of this program have been: (1) the development of experimental and computational data to evaluate the optimum performance of fracture-stimulated geothermal reservoirs; (2) the development of a geothermal reservoir model to evaluate important thermophysical, hydrodynamic, and chemical parameters based on fluid-energy-volume balances as part of standard reservoir engineering practice; and (3) the construction of a laboratory model of an explosion-produced chimney to obtain experimental data on the processes of in-place boiling, moving flash fronts, and two-phase flow in porous and fractured hydrothermal reservoirs

Decomposition of NO studied by infrared emission and CO laser absorption

A diagnostic technique for monitoring the concentration of NO using absorption of CO laser radiation was developed and applied in a study of the decomposition kinetics of NO. Simultaneous measurements of infrared emission by NO at 5.3 microns were also made to validate the laser absorption technique. The data were obtained behind incident shocks in NO-N2O-Ar (or Kr) mixtures, with temperatures in the range 2400-4100 K. Rate constants for dominant reactions were inferred from comparisons with computer simulations of the reactive flow

A detector for continuous measurement of ultra-cold atoms in real time

We present the first detector capable of recording high-bandwidth real time atom number density measurements of a Bose Einstein condensate. Based on a two-color Mach-Zehnder interferometer, our detector has a response time that is six orders of magnitude faster than current detectors based on CCD cameras while still operating at the shot-noise limit. With this minimally destructive system it may be possible to implement feedback to stabilize a Bose-Einstein condensate or an atom laser.Comment: 3 pages, 3 figures, submitted to optics letter

VARIABLY CURING RESINS FOR MOUNTING METALLOGRAPHIC SAMPLES

In the past, heat-and-pressure-curing resins have been used almost exclusively as mounting materials for metallographic samples. Now, however, certain polyester resins, which are curable at room temperature, are equally as good for this purpose, and with their versatility they adapt readily to a variety of mounting conditions. A study of the epoxies and polyesters was made to determine which type of resin would satisfy the desirable properties of a metallographic mount. Four polyester resins were selected and investigated intensively to ascertain the variables associated with their curing processes. The results are compared with the standard thermosetting mounting material, Bakelite. (auth

The NASA/GSFC hydrogen maser program: A review of recent data

Data is presented on the phase and frequency stability, over time periods extending to one week, of the new NR field operable hydrogen masers developed by the Applied Physics Laboratory (APL) and the older NX and NP field operable hydrogen masers developed by Goddard Space Flight Center and maintained and upgraded by Bendix Field Engineering Corporation (BFEC). Data is presented on the NR masers in the laboratory showing frequency stabilities well into the 10 to the -15th power range and phase stabilities well into the 100 ps range for periods of up to one day. Data is presented on upgraded NP masers in the laboratory showing that the frequency stability has been improved substantially to virtually the NR level. VLBI data is presented on the phase difference between NX-2 at Owens Valley, California and NR-2 at Fort Davis, Texas for a one week period showing, after removal of a constant frequency drift, a 350 ps RMS phase stability

The influence of cell phone users' relationship intentions on expectations and perceptions of service recovery

With the first-time cell phone user market quickly shrinking, it is becoming increasingly important for South African cell phone network providers to retain customers by building long-term relationships with them and consistently offering quality service. Despite cell phone network providers' best intentions, service failures do occur. Not all customers want to build relationships with cell phone network providers, and therefore it is important to consider the influence of customers' relationship intentions within a service failure and recovery setting. The purpose of the study was to determine the influence of relationship intention on expectations and perceptions of two service recovery scenarios within the cell phone industry. Non-probability convenience sampling was used to collect data from 605 cell phone users residing in Gauteng. Results indicate that as respondents' relationship intentions increase, so do their expectations that their cell phone network providers should take service recovery action. It was also found that respondents with high and moderate relationship intentions perceived service recovery strategies of their cell phone network providers including an acknowledgement, apology, explanation and rectification of the problem more favourable, compared to a service recovery strategy only rectifying the problem, than those respondents with low relationship intentions

Young adults’ relationship intentions towards their cell phone network operators

Marketers use relationship marketing to establish mutually beneficial long-term relationships with their customers as a means to retain them in the competitive market environment. Relationship marketing should not be used to target every customer as not all customers want to build long-term relationships with organisations. In order to identify the most profitable customers for relationship marketing, organisations should consider their customers’ relationship intentions to form long-term relationships with them. The primary objective of this study was to determine young adults’ (aged 18 to 25) relationship intentions towards the South African cell phone network operators they use, namely Vodacom, MTN or Cell C. Five constructs (involvement, expectations, forgiveness, feedback and fear of relationship loss) were used to measure relationship intention. Data was collected from 315 respondents at a tertiary education institution in South Africa by means of a non-probability convenience sample. Findings indicate that a relatively high percentage of respondents have a high relationship intention towards their cell phone network operator and that respondents with high relationship intentions are more Involved with and Fear losing their relationship with their cell phone network operator than respondents with low relationship intention

Transcutaneous electrical nerve stimulation in the treatment of myofascial pain dysfunction

PKThe effect of transcutaneous electrical nerve stimulation (TENS) plus conservative therapy (ibuprofen, bite plate, self-physiotherapy) on myofascial pain dysfunction (MPD) was determined. A single-blind trial as done in 10 patients with MPD with subthreshold TENS (frequency 35 Hz, pulse width 100 milliseconds, modulation 50%) compared with sham TENS at 8 visits over 14 weeks. Pain was assessed on a visual analogue scale before and after TENS at each visit and the data were analysed with the analysis of variance (ANOVA) for repeated measures. A highly significant effect was seen for time (F = 4.80, P = 0.0003) but not for TENS. Subthreshold TENS did not increase the symptom relief produced by conservative treatment with the protocol used

The Evolutionary Status of Isolated Dwarf Irregular Galaxies II. Star Formation Histories and Gas Depletion

The results of UBV and H alpha imaging of a large sample of isolated dwarf irregular galaxies are interpreted in the context of composite stellar population models. The observed optical colors are best fit by composite stellar populations which have had approximately constant star formation rates for at least 10 Gyr. The galaxies span a range of central surface brightness, from 20.5 to 25.0 mag arcsec^{-2}; there is no correlation between surface brightness and star formation history. Although the current star formation rates are low, it is possible to reproduce the observed luminosities without a major starburst episode. The derived gas depletion timescales are long, typically ~20 Gyr. These results indicate that dwarf irregular galaxies will be able to continue with their slow, but constant, star formation activity for at least another Hubble time. The sample of isolated dIs is compared to a sample of star bursting dwarf galaxies taken from the literature. The star bursting dwarf galaxies have many similar properties; the main difference between these two types of gas-rich dwarf galaxies is that the current star formation is concentrated in the center of the star bursting systems while it is much more distributed in the quiescent dIs. This results in pronounced color gradients for the starbursting dwarf galaxies, while the majority of the quiescent dwarf irregular galaxies have minor or non-existent color gradients. Thus, the combination of low current star formation rates, blue colors, and the lack of significant color gradients indicates that star formation percolates slowly across the disk of normal dwarf galaxies in a quasi-continuous manner.Comment: 16 pages, uses emulateapj, to appear in The Astronomical Journal (April 2001

Naturally Rehearsing Passwords

We introduce quantitative usability and security models to guide the design of password management schemes --- systematic strategies to help users create and remember multiple passwords. In the same way that security proofs in cryptography are based on complexity-theoretic assumptions (e.g., hardness of factoring and discrete logarithm), we quantify usability by introducing usability assumptions. In particular, password management relies on assumptions about human memory, e.g., that a user who follows a particular rehearsal schedule will successfully maintain the corresponding memory. These assumptions are informed by research in cognitive science and validated through empirical studies. Given rehearsal requirements and a user's visitation schedule for each account, we use the total number of extra rehearsals that the user would have to do to remember all of his passwords as a measure of the usability of the password scheme. Our usability model leads us to a key observation: password reuse benefits users not only by reducing the number of passwords that the user has to memorize, but more importantly by increasing the natural rehearsal rate for each password. We also present a security model which accounts for the complexity of password management with multiple accounts and associated threats, including online, offline, and plaintext password leak attacks. Observing that current password management schemes are either insecure or unusable, we present Shared Cues--- a new scheme in which the underlying secret is strategically shared across accounts to ensure that most rehearsal requirements are satisfied naturally while simultaneously providing strong security. The construction uses the Chinese Remainder Theorem to achieve these competing goals