Coherent communication link using diode-pumped lasers

Work toward developing a diffraction limited, single frequency, modulated transmitter suitable for coherent optical communication or direct detection communication is discussed. Diode pumped, monolithic Nd:YAG nonplanar ring oscillators were used as the carrier beam. An external modulation technique which can handle high optical powers, has moderate modulation voltage, and which can reach modulation rates of 1 GHz was invented. Semiconductor laser pumped solid-state lasers which have high output power (0.5 Watt) and which oscillate at a single frequency, in a diffraction limited beam, at the wavelength of 1.06 microns were built. A technique for phase modulating the laser output by 180 degrees with a 40-volt peak to peak driving voltage is demonstrated. This technique can be adapted for amplitude modulation of 100 percent with the same voltage. This technique makes use of a resonant bulk modulator, so it does not have the power handling limitations of guided wave modulators

Preprocessing versus search processing for constraint satisfaction problems

A perennial problem in hybrid backtrack CSP search is how much local consistency processing should be done to achieve the best efficiency. This can be divided into two separate questions: (1) how much work should be done before the actual search begins, i.e. during preprocessing? and (2) how much of the same processing should be interleaved with search? At present there are two leading approaches to establishing stronger consistencies than the basic arc consistency maintenance that is done in most solvers. On the one hand there are various kinds singleton arc consistency that can be used; on the other there are several variants of restricted path consistency. To date these have not been compared directly. The present work attempts to do this for a variety of problems, and in so doing, it also provides an empirical evaluation of the preprocessing versus search processing issue. Comparisons are made using the domain/degree and domain/weighted degree variable ordering heuristics. In general, it appears that preprocessing with higher levels of consistency followed by hybrid-AC processing (i.e. MAC) gives the best results, especially when the weighted degree heuristic is used. For problems with n-ary constraints, this difference seems to be even more pronounced. In some cases, higher levels of consistency maintenance established during preprocessing leads to performance gains over MAC of several orders of magnitude

Conditional lexicographic orders in constraint satisfaction problems

The lexicographically-ordered CSP ("lexicographic CSP" or "LO-CSP" for short) combines a simple representation of preferences with the feasibility constraints of ordinary CSPs. Preferences are defined by a total ordering across all assignments, such that a change in assignment to a given variable is more important than any change in assignment to any less important variable. In this paper, we show how this representation can be extended to handle conditional preferences in two ways. In the first, for each conditional preference relation, the parents have higher priority than the children in the original lexicographic ordering. In the second, the relation between parents and children need not correspond to the importance ordering of variables. In this case, by obviating the "overwhelming advantage" effect with respect to the original variables and values, the representational capacity is significantly enhanced. For problems of the first type, any of the algorithms originally devised for ordinary LO-CSPs can also be used when some of the domain orderings are dependent on assignments to "parent" variables. For problems of the second type, algorithms based on lexical orders can be used if the representation is augmented by variables and constraints that link preference orders to assignments. In addition, the branch-and-bound algorithm originally devised for ordinary LO-CSPs can be extended to handle CSPs with conditional domain orderings

Prototype laser-diode-pumped solid state laser transmitters

Monolithic, diode-pumped Nd:YAG ring lasers can provide diffraction-limited, single-frequency, narrow-linewidth, tunable output which is adequate for use as a local oscillator in a coherent communication system. A laser was built which had a linewidth of about 2 kHz, a power of 5 milliwatts, and which was tunable over a range of 30 MHz in a few microseconds. This laser was phase-locked to a second, similar laser. This demonstrates that the powerful technique of heterodyne detection is possible with a diode-pumped laser used as the local oscillator. Laser diode pumping of monolithic Nd:YAG rings can lead to output powers of hundreds of milliwatts from a single laser. A laser was built with a single-mode output of 310 mW. Several lasers can be chained together to sum their power, while maintaining diffraction-limited, single frequency operation. This technique was demonstrated with two lasers, with a total output of 340 mW, and is expected to be practical for up to about ten lasers. Thus with lasers of 310 mW, output of up to 3 W is possible. The chaining technique, if properly engineered, results in redundancy. The technique of resonant external modulation and doubling is designed to efficiently convert the continuous wave, infrared output of our lasers into low duty-cycle pulsed green output. This technique was verified through both computer modeling and experimentation. Further work would be necessary to develop a deliverable system using this technique

Generalizing inconsistency learning for constraint satisfaction

Constraint satisfaction problems, where values are sought for problem variables subject to restrictions on which combinations of values are acceptable, have many applications in artificial intelligence. Conventional learning methods acquire individual tuples of inconsistent values. These learning experiences can be generalized. We propose a model of generalized learning, based on inconsistency preserving mappings, which is sufficiently focused so as to be computationally cost effective. Rather than recording an individual inconsistency that led to a failure, and looking for that specific inconsistency to recur, we observe the context of a failure, and then look for a related context in which to apply our experience opportunistically. As a result we leverage our learning power. This model is implemented, extended and evaluated using two simple but important classes of constraint problems

Is Attendance Really Declining at Games?: An Analysis of Walk-ins Versus Web Counts

Objectives: The purpose is to see if there is a relationship between declining walk-in visitor counts and increased library web access. The overall objective is to evaluate library services and find better and more efficient ways to meet the needs of walk-in and virtual patrons. Methods: Compile past five years of walk-in visitor statistics from the library. Retrieve past five years of website statistics from Google Analytics. These two sets of data will be compared and analyzed for any correlation. We hypothesize the data will show a steady decrease in walk-in visitors along with a continued increase in website visitors. We hope to find a period during the past five years where the two values intersect. If a clear relation exists, we will identify possible factors that can be attributed to these changes. Results: The combination of online “visits” combined with walkin visits gives an entirely different picture of the use of libraries by patrons. Conclusion: Librarians should not be wedded to success markers of past eras. By updating measures of recording “attendance,” a more truthful picture emerges about the true popularity of libraries. This type of data is essential, since libraries are under more pressure to justify their existence

Making a Difference through Fundraising

Objectives: The US healthcare system will have to exist on reduced funding in the future, creating a need for new funding sources for health science libraries to survive. The purpose of this study is to investigate funraising in academic allopathic medical libraries. Methods: A cross-sectional methodology was implemented. An electronic survey was utilized to ask fifteen fundraising questions to participants. The questions consisted of: current status of library fundraising, perceptions of the central development office, utilizing fundraising positions inside the library, types of fundraising activities used, most successul fundraising positions inside the library, five year fundraising income, fundraising advertising, utilization of funds, challenges and motivations to fundraising, and donor recognition. These questions were loaded onto checkbox survey software for distribution. The survey was distributed to five members of a blinded focus group for testing. Potential academic medical library groups were identifitied that have academic medical libraries with diverse sizes and budgets. The decision to use CONBLS consortium was decided based on these factors. Results: An email letter containing a survey link and cover letter was sent to all 21 CONBLS members. Usable responses wree received from 15 institutions, or 71.4% of the libraries. Descriptive statistics were used to analyze the responses to specific questions. Conclusions: Academic medical libraries in the Southeast region are highly interested in fundraising, but less than half of the libraries consider themselves active fundraisers. Many challenges associated with establishing an active fundraising program exist. Similar fundraising challenges exist in general academic libraries and medical library professionals should reference this literature. In order to improve these statistics, educating directors on fundraising at group levels as CONBLS, SCMLA, and ALADN would help encourage discussion and promote larger fundraising efforts. Establishing key relationships on campus is important for academic medical libraries to establish a continuous cycle of fundraising

A Mixed-Methods Analysis of a Library-Based Hand-Held Intervention with Rural Clinicians

Background: The East Tennessee State University Quillen College of Medicine Library has participated for several years in projects to provide rural clinicians with health information resources. Objectives: To determine whether a strategy of hand‐held devices with a best‐evidence point‐of‐care disease tool and a drug database paired with access to a medical library for full‐text articles and training to use the tools would be an affordable way to meet the information needs of rural underserved clinicians. Methods: This study is a mixed‐methods methodology. The first project was evaluated using a randomised controlled trial (RCT) methodology. The second was evaluated qualitatively using interviews and focus groups. Results: The quantitative findings discovered that clinicians equipped with a hand‐held device with evidence‐based software more frequently found answers to clinical questions, found answers more quickly, were more satisfied with information they found and use expensive resources such as continuing medical education, online databases and textbooks less than the group that did not have access to online technology. Qualitative results supported the quantitative findings. Conclusion: Librarians can implement a three‐pronged strategy of the secondary literature via a hand‐held, the primary literature via Loansome Doc and quality training to meet basic information needs of rural clinicians

Partial (neighbourhood) singleton arc consistency for constraint satisfaction problems

Algorithms based on singleton arc consistency (SAC) show considerable promise for improving backtrack search algorithms for constraint satisfaction problems (CSPs). The drawback is that even the most efficient of them is still comparatively expensive. Even when limited to preprocessing, they give overall improvement only when problems are quite difficult to solve with more typical procedures such as maintained arc consistency (MAC). The present work examines a form of partial SAC and neighbourhood SAC (NSAC) in which a subset of the variables in a CSP are chosen to be made SAC-consistent or neighbourhood-SAC-consistent. These consistencies are well-characterized in that algorithms have unique fixpoints and there are well-defined dominance relations. Heuristic strategies for choosing an effective subset of variables are described and tested, in particular a strategy of choosing by constraint weight after random probing. Experimental results justify the claim that these methods can be nearly as effective as full (N)SAC in terms of values discarded while significantly reducing the effort required