Broadband Amplification of Low-Terahertz Signals Using Axis-Encircling Electrons in a Helically Corrugated Interaction Region.

Experimental results are presented of a broadband, high power, gyrotron traveling wave amplifier (gyro-TWA) operating in the (75-110)-GHz frequency band and based on a helically corrugated interaction region. The second harmonic cyclotron mode of a 55-keV, 1.5-A, axis-encircling electron beam is used to resonantly interact with a traveling TE_{21}-like eigenwave achieving broadband amplification. The gyro-TWA demonstrates a 3-dB gain bandwidth of at least 5.5 GHz in the experimental measurement with 9 GHz predicted for a wideband drive source with a measured unsaturated output power of 3.4 kW and gain of 36-38 dB. The approach may allow a gyro-TWA to operate at 1 THz.

Experimental Demonstration of a Resonator-Induced Phase Gate in a Multiqubit Circuit-QED System.

The resonator-induced phase (RIP) gate is an all-microwave multiqubit entangling gate that allows a high degree of flexibility in qubit frequencies, making it attractive for quantum operations in large-scale architectures. We experimentally realize the RIP gate with four superconducting qubits in a three-dimensional circuit-QED architecture, demonstrating high-fidelity controlled-z (cz) gates between all possible pairs of qubits from two different 4-qubit devices in pair subspaces. These qubits are arranged within a wide range of frequency detunings, up to as large as 1.8 GHz. We further show a dynamical multiqubit refocusing scheme in order to isolate out 2-qubit interactions, and combine them to generate a 4-qubit Greenberger-Horne-Zeilinger state.

Generation of electromagnetic fields of extremely high intensity by coherent summation of Cherenkov superradiance pulses.

We demonstrate both theoretically and experimentally the possibility of correlating the phase of a Cherenkov superradiance (SR) pulse to the sharp edge of a current pulse, when spontaneous emission of the electron bunch edge serves as the seed for SR processes. By division of the driving voltage pulse across several parallel channels equipped with independent cathodes we can synchronize several SR sources to arrange a two-dimensional array. In the experiments carried out, coherent summation of radiation from four independent 8-mm wavelength band SR generators with peak power 600 MW results in the interference maximum of the directional diagram with an intensity that is equivalent to radiation from a single source with a power of 10 GW.

High power wideband gyrotron backward wave oscillator operating towards the terahertz region.

Experimental results are presented of the first successful gyrotron backward wave oscillator (gyro-BWO) with continuous frequency tuning near the low-terahertz region. A helically corrugated interaction region was used to allow efficient interaction over a wide frequency band at the second harmonic of the electron cyclotron frequency without parasitic output. The gyro-BWO generated a maximum output power of 12 kW when driven by a 40 kV, 1.5 A, annular-shaped large-orbit electron beam and achieved a frequency tuning band of 88-102.5 GHz by adjusting the cavity magnetic field. The performance of the gyro-BWO is consistent with 3D particle-in-cell numerical simulations.

Experimental and theoretical studies of a coaxial free-electron maser based on two-dimensional distributed feedback.

The first operation of a coaxial free-electron maser (FEM) based on two-dimensional (2D) distributed feedback has been recently observed. Analytical and numerical modeling, as well as measurements, of microwave radiation generated by a FEM with a cavity defined by coaxial structures with a 2D periodic perturbation on the inner surfaces of the outer conductor were carried out. The two-mirror cavity was formed with two 2D periodic structures separated by a central smooth section of coaxial waveguide. The FEM was driven by a large diameter (7 cm), high-current (500 A), annular electron beam with electron energy of 475 keV. Studies of the FEM operation have been conducted. It has been demonstrated that by tuning the amplitude of the undulator or guide magnetic field, modes associated with the different band gaps of the 2D structures were excited. The Ka-band FEM generated 15 MW of radiation with a 6% conversion efficiency, in good agreement with theory.

Experimental study of coaxial free-electron maser based on two-dimensional distributed feedback.

The first experimental study of a coaxial free-electron maser (FEM) based on two-dimensional (2D) distributed feedback is presented. A new type of cavity formed with coaxial 2D surface photonic band gap structures was used. The FEM was driven by a large diameter (7 cm), high-current (500 A), annular electron beam of energy 475 keV. By tuning the amplitude of the undulator or guide magnetic field, modes associated with the different band gaps of the 2D structures were excited. The -band coaxial FEM generated 15 MW of radiation with a 6% conversion efficiency, in excellent agreement with theory.

Dispersion of helically corrugated waveguides: analytical, numerical, and experimental study.

Helically corrugated waveguides have recently been studied for use in various applications such as interaction regions in gyrotron traveling-wave tubes and gyrotron backward-wave oscillators and as a dispersive medium for passive microwave pulse compression. The paper presents a summary of various methods that can be used for analysis of the wave dispersion of such waveguides. The results obtained from an analytical approach, simulations with the three-dimensional numerical code MAGIC, and cold microwave measurements are analyzed and compared.

Compression of frequency-modulated pulses using helically corrugated waveguides and its potential for generating multigigawatt rf radiation.

A new method to generate ultrahigh-power microwave pulses compatible with mildly relativistic electron sources is proposed. This method involves a novel microwave compressor in the form of a metal helically corrugated waveguide, which can enhance the power of frequency-modulated nanosecond pulses up to the multigigawatt level. The results of the proof-of-principle experiments at kilowatt power levels are in good agreement with theory.

Experimental studies of the influence of distributed power losses on the transparency of two-dimensional surface photonic band-gap structures.

Two-dimensional (2D) surface photonic band-gap (SPBG) structures have been suggested to realize 2D distributed feedback. The 2D SPBG structures can be obtained by providing 2D periodic perturbations of the waveguide surface. Such a structure can be used in a wide variety of applications including microwave electronics and integrated optics. The theoretically predicted effect of the transparency of the 2D SPBG structure when distributed Ohmic losses inside the structure are relatively high in comparison with the wave coupling coefficient has been observed in a series of experiments. The results obtained are in good agreement with theoretical predictions.

Social support and psychological functioning among high-risk mothers: the impact of the Baby Love Maternal Outreach Worker Program.

This study compared two groups of high-risk Medicaid-eligible mothers, 221 who participated in a maternal home visitation program and 198 who did not, to determine whether program participation was associated with improvements in the mothers' psychological functioning 1 year after delivery, and whether these improvements were associated with the type and intensity of support provided by home visitors. The results suggest that, compared to nonparticipants, participants provided with more intensive home visitor support had significantly higher self-esteem (p = 0.039) and were less depressed (p = 0.015). Participants with less intensive home visitor support, however, did not differ significantly from nonparticipants in their self-esteem or depression levels. No significant differences were observed in the perceived stress levels of participants as compared with nonparticipants, regardless of the intensity of home visitor support. Mothers who had support from the baby's father, however, had significantly lower perceived stress levels than mothers with no support from the baby's father (p = 0.046). Moreover, the type of support provided by home visitors (emotional, instrumental, informational) did not appear to be related to the mothers' psychological functioning. This study suggests that the intensity of support is an important component of maternal home visitation programs that aim to improve women's psychological functioning.

Factors predicting completion of a home visitation program by high-risk pregnant women: the North Carolina Maternal Outreach Worker Program.

OBJECTIVES: This study sought to identify characteristics of high-risk pregnant women that predicted long-term participation in a home visitation program. METHODS: Data regarding sociodemographic characteristics, perceived needs, psychological functioning, substance use, and informal social support were collected prospectively from 152 short-term and 221 long-term program participants. RESULTS: In comparison with short-term participants, long-term participants were more likely to have been African American, married, nonsmokers, and enrolled in the program during their second trimester of pregnancy, and they were more likely to have had emotional and instrumental support needs. CONCLUSIONS: Women with greater social support needs and healthier behaviors were more receptive to long-term home visitation than other women.

Theory and design of a free-electron maser with two-dimensional feedback driven by a sheet electron beam.

The use of two-dimensional Bragg resonators of planar geometry, realizing two-dimensional (2D) distributed feedback, is considered as a method of producing spatially coherent radiation from a large sheet electron beam. The spectrum of eigenmodes is found for a 2D Bragg resonator when the sides of the resonator are open and also when they are closed. The higher selectivity of the open resonator in comparison with the closed one is shown. A time-domain analysis of the excitation of an open 2D Bragg resonator by a sheet electron beam demonstrates that a single-mode steady-state oscillation regime may be obtained for a sheet electron beam of width 100-1000 wavelengths. Nevertheless, for a free-electron maser (FEM) with a closed 2D Bragg resonator, a steady-state regime can also be realized if the beam width does not exceed 50-100 wavelengths. The parameters for a FEM with a 2D planar Bragg resonator driven by a sheet electron beam based on the U-2 accelerator (INP RAS, Novosibirsk) are estimated and the project is described.

Generation of powerful subnanosecond microwave pulses by intense electron bunches moving in a periodic backward wave structure in the superradiative regime.

Experimental results of the observation of coherent stimulated radiation from subnanosecond electron bunches moving through a periodic waveguide and interacting with a backward propagating wave are presented. The subnanosecond microwave pulses in Ka and W bands were generated with repetition frequencies of up to 25 Hz. The mechanism of microwave pulse generation was associated with self-bunching, and the mutual influence of different parts of the electron pulse due to slippage of the wave with respect to the electrons; this can be interpreted as superradiance. The illumination of a panel of neon bulbs resulted in a finely structured pattern corresponding to the excitation of the TM01 mode. Observation of rf breakdown of ambient air, as well as direct measurements by hot-carrier germanium detectors, leads to an estimate of the absolute peak power as high as 60 MW for the 300-ps pulses at 38 GHz. These results are compared with numerical simulations. The initial observation of 75-GHz, 10-15-MW radiation pulses with a duration of less than 150 ps is also reported.

State health department and university evaluation of North Carolina's Maternal Outreach Worker Program.

INTRODUCTION: The Maternal Outreach Worker (MOW) Program is a social support intervention using lay helpers to provide support, health education, and outreach to Medicaid eligible women at risk for poor pregnancy and parenting outcomes. State Health Department and University collaborators designed a two-pronged evaluation comprised of programwide and interview study components to assess the impact of the program on pregnancy outcomes, health behaviors, and infant health status. METHODS: Programwide evaluation data are based on 1992-1995 N.C. birth files for the original 24 participating counties and include 1,726 MOW participant births and 12,988 comparison births whose records were linked to birth files and met the study criteria. For the interview study 373 MOW participants and 332 comparison women were personally interviewed three times: during pregnancy, one month postpartum, and one year after delivery. RESULTS: Risk factors associated with poor pregnancy and parenting outcomes were greater among MOW participants than comparisons in both the programwide and intensive study components. Caucasian MOW participants had slightly higher rates of adequate prenatal care. African Americans were found to have less adequate prenatal care. Fewer than expected LBW and VLBW births were observed for African-American MOW participants. MOW Program participation did not affect the utilization of health and social services for infants. African Americans, regardless of whether they received MOW services, fared better than Caucasians in terms of having their pregnancy needs fulfilled. CONCLUSIONS: Findings show the need to further explore appropriate measures of maternity support program outcomes and indicate inconsistent program benefit among subpopulations.

Health outcomes of children receiving EPSDT checkups: a pilot study.

This pilot study used medical records to examine the health outcomes of children receiving care in Medicaid's Early and Periodic Screening, Diagnosis and Treatment (EPSDT) program. Medical records from 76 children seen for EPSDT visits during a 6-month period were reviewed to assess whether health problems were identified and whether treatment, follow-up, or referral care was provided. Health problems were identified for 43% of the children; 22% received treatment, and 18% were referred for specialty care. Checkups uncovered fewer problems than would be expected in a poor, largely minority population. Almost one third of the children referred for specialty care apparently did not receive such care. The study verified the need for further research and provides direction for future study.

Comprehensiveness of well child checkups for children receiving Medicaid: a pilot study.

Early and Periodic Screening, Diagnosis, and Treatment (EPSDT) is a Medicaid program designed to provide comprehensive well child care for children from low-income families. Each EPSDT checkup should include a physical examination; medical history; assessment of development, nutrition, and immunizations; assessment of hearing, vision, and dental status; and anticipatory guidance. This pilot study of the medical records of 76 children receiving EPSDT checkups in six rural counties in North Carolina provided a preliminary assessment of whether EPSDT checkups included the required components. The study showed that health care providers frequently did not provide adequate documentation of the care provided at the checkup, and it raised questions as to whether children received the required components of the EPSDT checkup.

Demographic and health characteristics of participants and nonparticipants in a work site health-promotion program.

Work site health-promotion programs represent an increasingly common attempt by industry to improve the health of employees. The potential impact of programs is limited by nonparticipation, especially among demographic subgroups and those who could most benefit from health behavior change. The present study prospectively examined the relationship of personnel data and self-reported health habits and health status to participation in the health-promotion program at a research and development work site. Thirty-four percent of the 505 employees enrolled in the health-promotion program. White employees were 2.47 times as likely to participate as nonwhites (95% confidence interval, 1.59, 3.83). Those with health maintenance organization health insurance were 1.43 times as likely to participate as were employees with fee-for-service insurance (1.11, 1.84). There was no difference between participants and nonparticipants in self-reported health status, and only slightly more positive health habits were noted among participants. Seatbelt use was 1.65 times more common among participants (1.10, 2.49). The study results are reassuring that such programs do not enroll only the very healthy or those with healthy habits. However, the diminished enrollment of nonwhite employees supports concern that health-related programs may not equally reach all segments of the work force.

Psychosocial predictors of participation in a work site health-promotion program.

An understanding of psychosocial factors associated with participation in health promotion programs could lead to targetted interventions to increase enrollment. This study used questionnaires to measure employees' perception of program efficacy, health attitudes, beliefs, social support, and stress prior to the introduction of a comprehensive health promotion program at a research and development work site. The association of these factors with enrollment in the program was then prospectively determined. In addition, open-ended questionnaires were used retrospectively to determine additional factors associated with participation. Of the above factors, only program efficacy was significantly associated with participation in the entire sample. Perceived social support was associated with participation among non-white employees. In open-ended questionnaires, a desire for health information, a desire for help with behavior change, and concern about health status were the most commonly given reasons for participating. The study findings imply that environmental factors operating during the enrollment period at the work site may be more powerful than preexisting attitudes and beliefs in determining participation.

Infant mortality: a practical approach to the analysis of the leading causes of death and risk factors.

The analysis of infant mortality data provides an opportunity for developing preventive strategies to improve this indicator of a population's health. All infant deaths in North Carolina during a 5-year period (1980 through 1984) were analyzed using the International Classification of Diseases, 9th revision (ICD-9), and a system for linked birth and death records that allows the analysis of birth certificate information on deaths. Causes of death were aggregated based on common etiology such as prematurity or obstetric-related conditions rather than the more traditional organ system taxonomy of the ICD-9 codes. Analyses were carried out separately for very low birth weight (less than or equal to 1500 g), moderately low birth weight (1501 through 2500 g), and normal birth weight (greater than 2500 g) babies. Maternal characteristics identified from the birth certificate were also compared with the different causes of death. Prematurity-related conditions accounted for 37.5% of all deaths, ranking far above the 17.4% for congenital anomalies and 12.9% for sudden infant death syndrome. For normal birth weight babies, sudden infant death syndrome ranked first, followed by congenital anomalies and nonperinatal infections. For the moderately low birth weight babies, congenital anomalies ranked first, with sudden infant death syndrome second and prematurity-related conditions third. For the very low birth weight babies, prematurity-related conditions accounted for nearly 70% of the deaths, with obstetric conditions and congenital anomalies ranking second and third, respectively. Maternal risk factors identified an overrepresentation of nonwhite, unmarried, and young teenage mothers and mothers with less than adequate prenatal care.(ABSTRACT TRUNCATED AT 250 WORDS)