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The acoustic bubble is an example of a highly nonlinear system which is the building block of several applications and phenomena ranging from underwater acoustics to sonochemistry and medicine. Nonlinear behavior of bubbles, and most importantly 1/2 order subharmonics (SH), are used to increase the contrast to tissue ratio (CTR) in diagnostic ultrasound (US) and to monitor bubble mediated therapeutic US. It is shown experimentally and numerically that when bubbles are sonicated with their SH resonance frequency (fsh=2fr where fr is the linear resonance frequency), SHs are generated at the lowest excitation pressure. SHs then increase rapidly with pressure increase and reach an upper limit of the achievable SH signal strength. Numerous studies have investigated the pressure threshold of SH oscillations; however, conditions to enhance the saturation level of SHs has not been investigated. In this paper nonlinear dynamics of bubbles excited by frequencies in the range of fr

Period doubling route to chaos is one of the well-known characteristics of nonlinear oscillators. A bubble is a highly nonlinear oscillator that exists in various phenomena and applications ranging from material science and underwater acoustics to medical ultrasound. The occurrence of period doubling (PD) in the oscillations of the bubbles is concomitant with the generation of 1/2 order subharmonics (SHs). SH oscillations are used to monitor the bubble activity and are employed as a measure of stable cavitation. As bubbles are intravascular contrast agents, SH oscillations are used in diagnostic ultrasound to increase the contrast of the blood vessels to the tissue. Despite the importance of PD in a bubble oscillator, the dynamical behavior of the bubble during stable SH and ultra-harmonic (UH) oscillations have not thoroughly studied yet. In this work, through applying a comprehensive bifurcation method, we study the nonlinear radial oscillations of the bubble oscillator as a function of ultrasound driving pressure. The frequency of the driving force is chosen as the linear resonance frequency (fr) and linear SH resonance frequency (fsh=2fr) of the bubble. Results show that, when the bubble is sonicated with 2fr, PD doubling occurrence is more likely to result in non-destructive oscillations. The evolution of the bubble stable P2 dynamics forms the shape of a bow-tie for bubbles with an initial diameter of 740nm and above. When f=2fr, the phase portrait of the P2 attractor is distinctly different from a P2 attractor when f=fr, and SH component of the backscattered pressure is maximum. When sonicated by 2fr, due to lower oscillation amplitude and gentler bubble collapse, the bubble can sustain stable P2 oscillations for a longer duration and over a broader range of applied acoustic pressure.

This report addresses the Virginia Community College System's (VCCS) core performance standards and measures for the years 2001-2002. There are four core indicators through which the VCCS is assessed. They are the following: (1) student attainment including academic and technical skills; (2) completion/graduation rate using first time, full-time freshmen; (3) placement and persistence rates which track students' employment rates and further study done in the future; and (4) equity: program enrollment and completion including a focus on "under-represented" programs. An exact definition is given for each of preceding indicators in the report as it is used in the document. These Perkins performance measure definitions were finalized with the Virginia and federal departments of education in the fall 2000. The report finds that for the 2001-02 cycle, the VCCS exceeded performance targets for 4 of the 7 broadly defined measure. There were increases for nontraditional students in nontraditional programs. The report displays the federally approved VCCS or system-level targets for the 2001-02 reporting cycle as well as college performance data for college and Workforce Development Services staff planning and evaluation activities. (MZ)

The 1990s saw a significant increase in the amount of technology used in the classroom and an increased need for individuals with high-tech skills. However, while this mass technology was being integrated, the human skills of instruction and advisement were being lost. Technology seemed to be negatively influencing the learning process. As a result, colleges have had to address the question of whether or not technology and academic procedures are providing an adequate learning environment. Technology should be used as a complementary part of the educational experience. At Patrick Henry Community College (Virginia), workshops and seminars in the fields of technology and interpersonal relations were scheduled to address this issue. After attending these workshops, faculty have found it easier to confer with one another and plan for better levels of service to customers; faculty are much more able to assist students with problems and questions; and students leave at graduation with credentials, certifications, and a greater knowledge of skills. Students are the direct beneficiaries of these workshops. Employers also benefit by receiving graduates with good interpersonal, problem-solving, and communication skills. (CJW)

This report documents the employment status of Virginia Community College System (VCCS) students. In fall 1996, all 24 colleges involved in the study had at least a 50% working student population, and nearly 41% of all VCCS students were working full-time and also taking classes. A profile of business and industry showed that community colleges serve employees from all segments of the Virginia economy, with retail trade being a major employer for younger students. In addition, VCCS students are employed at the majority of Virginia's information and high-technology firms. Major groups in the services sector, the largest employer of VCCS students, include health, business, education, and engineering-management. The study found that 1) though males and females have the same rates of employment, males are more likely to work full-time; 2) if they are working, white, black, and Hispanic students are most likely to have full-time jobs; 3) new students are less likely to be working than returning students; 4) most VCCS students attend class part-time and work full-time, with the percentage of full-time employees increasing with age up to the 60-and-over category; and 5) the 18-21 age group has the highest percentage of working students. (YKH)

The Virginia Community College System (VCCS) conducted a study of city and county population penetration rates, or the percentages of residents served by VCCS colleges. Using total in-state enrollment for fall 1997, the study found that the percentage of Virginia's population served by the VCCS increased to 1.82%, returning the system to the 1995-96 participation level. In the data tables provided, fall headcount is limited to college service region enrollments. Total population is based on projections developed by the State Data Center, Virginia Employment Commission (June 1993). The within-region penetration rate for the VCCS is 1.67%, up from 1.61% in 1996.. These rates are higher for colleges in the southwestern part of the state, the highest being 3.5% for Southwest Virginia Community College. Virginia's penetration rate nearly equals the national rate of 2.0%. Data tables of penetration rates are provided for the following VCCS colleges: Blue Ridge, Central Virginia, D.S. Lancaster, Danville, Eastern Shore, Germanna, J.S. Reynolds, John Tyler, Lord Fairfax, Mountain Empire, New River, Northern Virginia, Patrick Henry, Paul D. Camp, Piedmont VA, Rappahannock, Southside WV, Southwest VA, Thomas Nelson, Tidewater, Virginia Highlands, Virginia Western, and Wytheville. (YKH)

This paper explains the similarities and differences between electronic mail and computer conferencing, and identifies the features one should look for in a modern conferencing system. It also clarifies some related terminology. Advantages of computer conferencing are first outlined, including: time- and space- independence; text-based medium; permanent recording; document transfer; decreased turnaround time; access to online resources; an egalitarian context; improved access; overcoming social isolation and increasing emotional involvement; potential for improved participation; opportunity for increased interaction; enabling cooperative and collaborative group work; and enabling knowledge-building. Disadvantages of computer conferencing include the cost of technology; learning curve; technical difficulties; frustrations with group work; information overload; time spent online; and possible low levels of interaction. The following desirable features in computer conferencing software are then described: user-friendliness; cross-platform compatibility; basic word processing capabilities; client-server design; document transfer; conversation threading; ease of administration; digesting; affordability; high quality documentation; off-line work; multimedia capability; address book; batch processing; forms creation and integration; transparent integration with the Internet and World Wide Web; and chat. (Contains 14 references.) (AEF)

Computer conferencing (CC) is rapidly becoming a viable and useful adjunct to many distance education delivery systems. This paper deals with the general questions of what might constitute exemplary practice in using CC for teaching and learning, as well as features to look for when selecting a CC system. The "Do's" include: test the technology thoroughly; provide high quality instructional materials and documentation; provide high quality technical support; build CC skills gradually; provide study guides; make CC integral and relevant; plan for information management; plan for group development; keep discussions focused; specify expectations; use a variety of pedagogical techniques; and create discussion summaries. In a CC environment, there are also practices to avoid. These"don'ts" include: using computer mediated communication as an add-on; monopolizing and/or sermonizing; allowing any individuals to dominate; permitting inappropriate exchanges; including "fluff" in the course; and underestimating the work involved. (Contains 15 references.) (AEF)

This report describes graduation rates for the Virginia Community College System (VCCS) in 1994-95 using three different measures: cohort analysis, time to graduation, and a ratio of curriculum students to awards. The first section compares the use of two cohort analyses to determine graduation rates for students who entered in fall 1990. In the first method, the standard method used by the VCCS, career studies certificates are not included in the cohort, while in the second method, based on Student-Right-to-Know (SRK) regulations, career studies certificates are included but certificates earned after 2 years are not. This section indicates that using the "standard" cohort analysis, 18.2% of a cohort of 6,499 fall 1990 students graduated, while according to the SRK method 17.9% of a cohort of 6,594 students graduated. The second section examines completion rates in terms of the number of years and terms 1994-95 graduates took to complete a degree. This section indicates that 25% took 3 years to finish a two-year award, while the average median number of terms taken was 8 and the average median number of years was 4. The third section presents a simpler method of calculating a 1994-95 graduation rate, forming a ratio of the number of awards granted to the number of curriculum-placed students enrolled within the same year. Using this method, 14% of the curriculum-placed students in 1994-95 received awards. (TGI)

This article discusses psychophysical aspects of color perception and critically examines the advice on color use in screen design found in non-empirical literature. There are four main characteristics of color: hue, brightness, saturation, and contrast. In multimedia screen design, color can be used to link logically-related data; differentiate between required and optional data; highlight student errors; separate screen areas such as prompts, commands, or input/output fields; emphasize key points; and communicate overall structure. The following guidelines are identified and then categorized in terms of consistency, color choice, and coding and cueing with color: use color conservatively; limit the palette per screen; design for monochrome displays, and then add color; increase color with user experience; use colors selectively to manipulate attention; color material is generally processed faster than the same material in black-and-white; use color in formatting and graphic displays; electronically generated colors take on different properties in relation to each other; wavelength affects color differentiation; and changes in brightness may cause changes in hue for all colors except blue, green, and yellow. Aesthetically pleasing screens can employ scientifically derived principles of instructional design. One way to approach the convergence of science and opinion is through the four critical aspects of connoisseurship: (1) ability to make fine discriminations; (2) development of a hierarchical system of concepts for making judgements; (3) development of principles to describe the structure of relationships among concepts; and (4) development of strategies to focus on salient aspects of the item being judged. (Contains 66 references.) (AEF)

This paper summarizes the results of an analysis of literature on color use in screen design. Fundamental problems with the information base are identified as follows: (1) advise becomes obsolete as newer equipment becomes available; (2) the nature of the task used in the research is not sufficiently similar to tasks performed during teaching and learning; (3) generalizations are either apocryphal in origin or based on empirical results from different display media and transferred to video display terminals automatically; and (4) distinctions are not made with respect to intended uses of the screen display. Instructional designers must ascertain the currency of the equipment used before accepting research generalizations as guides; researchers and authors of literature reviews should indicate which generalizations might no longer be valid. A careful task analysis is necessary in order to maintain a high degree of similarity between the research tasks and actual teaching and learning strategies. Differences in display medium and textual presentation should be noted. There is a need for research on color use in the screen design for instruction. Three tables provide a classification of articles according to information type, tasks used in research, and a summary of empirical research studies is provided in three tables. (Contains 65 references.) (Author/AEF)

The Higher Order Techno Thinking (HOTT) Program was developed by a group of graduate students, who were experienced teachers, at the University of New Mexico. The objective was to develop an environment in which independent research, curriculum integration, multicultural awareness, and technology application could be integrated into a general or alternative learning environment. About 30 elementary and middle school students from varied educational settings, including one that combines home and classroom schooling, participated in the HOTT program. Each received instruction in using telecommunications technology. Each student then assumed the role of an individual from another culture, accessing information about the chosen character through information provided by " Mr. Data," a graduate student. Mr. Data answered questions individually and communicated with the students in ways that increased their enthusiasm and interest. The information allowed students to role-play and interact electronically. Student reactions were positive and teachers agreed that the program had promoted its objectives and allowed students to experience the power of high technology communication. HOTT taught that the computer is a tool and not merely a toy. (SLD)

Providing historical data on enrollment in the Virginia Community College System, this two-part report describes trends in enrollments and in minority student enrollment over the past decade. An introductory section reviews external factors influencing enrollment in Virginia, including revenue reductions, tuition increases, and the increasing student supply. Next, enrollment trends are described, including changes in the relationship of headcount to full-time equivalent students (FTES), course-taking patterns, student characteristics, first-time and returning student enrollments, and comparative tuition levels. This section indicates that 7 years of growth in FTES peaked in 1992-93, with 1993-94 FTES expected to decline; that the growth was due to increased enrollments in credit courses rather than increased numbers of students; and that from 1988 to 1993 enrollment in transfer programs increased from under 27,000 to 37,000. In part two, minority student enrollment is described for 1989-93, focusing on differences in enrollment by gender, student major, persistence and graduation, and financial aid eligibility for white, black, and other non-white groups. This section indicates that in fall 1989 white students accounted for 81% of enrollments, black students for 12%, and other groups for 7%, while in fall 1993, whites accounted for 76%, blacks for 15%, and other groups for 9%. Data tables by college are appended. (BCY)

In Fall 1994, the Virginia Community College System conducted two analyses of space utilization to compare actual facilities utilization in system colleges with state standards for space planning. The first study focused on the utilization of classrooms and class laboratories over the past 4 years, determining the percentages of the standard-use levels that spaces were actually in use. Results from this study included the following: (1) for classrooms, 4 of the system's 23 colleges exceeded the state standard for space utilization in 1994, with Mountain Empire College showing a rate of 117.4% of the standard; (2) for regular labs, 13 colleges exceeded the standard, while for heavy labs 5 colleges did so; (3) from 1992 to 1994, classroom utilization decreased for 11 colleges and increased for 6; (4) from 1992 to 1994, rates for heavy labs declined for 15 colleges and increased for 6; and (5) overall, station use remained steady or decreased slightly compared to 1992. The second study performed a similar analysis of use levels, but included classroom use for non-credit, continuing education courses to determine differences in utilization rates for the colleges. This study revealed that, in general, classroom-use rates improved for about two-thirds of the colleges, with six of these moving above the standard when the additional use was counted. As expected, however, neither heavy nor regular laboratory-use rates increased significantly. (Data tables are included.) (BCY)

To determine employment outcomes for graduates of the 1993-93 academic year, the Virginia Community College System (VCCS) undertook a study of outcomes by examining state unemployment insurance wage records. The analysis determined that for all 23 colleges in the system, 63.6% of graduates were employed by a Virginia business or industry at the end of 1993. Other findings included the following: (1) 43.8% of VCCS graduates were employed in service industries, 20.7% in retail trade, 12.6% in manufacturing, 6.4% in public administration, and 5.2% in finance, insurance, and real estate; (2) colleges with the highest percentages of employed graduates were Blue Ridge at 77.66%, J. Sargeant Reynolds at 74.71% Central Virginia at 74.68%, and Wytheville at 73.42%; (3) colleges with the lowest percentages of employed graduates were Mountain Empire at 54.37%, Northern Virginia at 53.74%, and Eastern Shore at 52.94%; (4) a further analysis of employees by type of employer revealed that 19.4% of the graduates employed in the service industries were employed in health services, the largest percentage; (5) VCCS program clusters employing the largest number of graduates were business at 1,513, public service at 1,427, and health at 1,215; and (6) the highest median salaries went to graduates from the health ($26,948), engineering and industrial ($23,396), and public services ($19,792) divisions. (KP)