Search PubMed⌕ Search

Biomedical subjects

C Urbina

Publications and source records attributed to C Urbina.

At least 19 recordsLinked to original sources
PubMed2002

Rabi oscillations in a large Josephson-junction qubit.

We have designed and operated a circuit based on a large-area current-biased Josephson junction whose two lowest energy quantum levels are used to implement a solid-state qubit. The circuit allows measurement of the qubit states with a fidelity of 85% while providing sufficient decoupling from external sources of relaxation and decoherence to allow coherent manipulation of the qubit state, as demonstrated by the observation of Rabi oscillations. This qubit circuit is the basis of a scalable quantum computer.

Journal Article↗
PubMed2002

Manipulating the quantum state of an electrical circuit.

We have designed and operated a superconducting tunnel junction circuit that behaves as a two-level atom: the "quantronium." An arbitrary evolution of its quantum state can be programmed with a series of microwave pulses, and a projective measurement of the state can be performed by a pulsed readout subcircuit. The measured quality factor of quantum coherence Qphi approximately 25,000 is sufficiently high that a solid-state quantum processor based on this type of circuit can be envisioned.

Journal Article↗
PubMed2001

Direct link between Coulomb blockade and shot noise in a quantum-coherent structure.

We analyze the current-voltage characteristic of a quantum conduction channel coupled to an electromagnetic environment with arbitrary frequency-dependent impedance. In the weak blockade regime the correction to the Ohmic behavior is directly related to the channel current fluctuations, vanishing at perfect transmission in the same way as shot noise. This relation can be generalized to describe the environmental Coulomb blockade in a generic mesoscopic conductor coupled to an external impedance, as the response of the latter to the current fluctuations in the former.

Journal Article↗
PubMed2001

Multiple-charge-quanta shot noise in superconducting atomic contacts.

We have measured shot noise in aluminum atomic point contacts containing a small number of conduction channels of known transmissions. In the normal state, we find that the noise power is reduced from its Poissonian value and reaches the partition limit, as calculated from the transmissions. In the superconducting state, the noise reveals the large effective charge associated with each elementary transfer process, in excellent agreement with the predictions of the quantum theory of multiple Andreev reflections.

Journal Article↗
PubMed2001

Multiple Andreev reflections revealed by the energy distribution of quasiparticles.

We have performed the tunnel spectroscopy of the energy distribution function of quasiparticles in 5-microm-long silver wires connected to superconducting reservoirs biased at different potentials. The distribution function f(E) presents several steps, which are manifestations of multiple Andreev reflections at the NS interfaces. The rounding of the steps is well explained by electron-electron interactions.

Journal Article↗
PubMed2001

Proximity effect and multiple Andreev reflections in gold atomic contacts.

We investigate the electronic transport properties of gold point contacts with superconducting aluminum leads. The modifications induced by the proximity effect in the quasiparticle density of states at the contact region are measured by tunnel spectroscopy. The theory of transport through multiple Andreev reflections is extended to incorporate these effects and used to determine the number and transmission coefficients of the conduction channels in the contact regime. We find that the smallest contacts, formed by one gold atom between the electrodes, contribute one single channel to the transport with variable transmission T between 0.1 and 1.

Journal Article↗
PubMed2000

Supercurrent in atomic point contacts and andreev states

We have measured the supercurrent in aluminum atomic point contacts containing a small number of well characterized conduction channels. For most contacts, the measured supercurrent is adequately described by the opposite contributions of two thermally populated Andreev bound states per conduction channel. However, for contacts containing an almost perfectly transmitted channel 0.9</=tau</=1 the measured supercurrent is higher than expected, a fact that we attribute to nonadiabatic transitions between bound states.

Journal Article↗
PubMed1999

Interdisciplinary ambulatory education and service in primary care at the University of New Mexico.

To compete and survive in a managed care market, academic health centers must develop integrated delivery systems in general and an integrated primary care system in particular. However, the departmental-based structure at most academic health centers is ill-suited to this purpose. Service and education are usually segregated by department, and the professional activities of primary care faculty in different departments are fragmented, leaving them weakened as a political force within the institution. The University of New Mexico established a model of integrated primary care education and service by creating three interdisciplinary primary care clinics staffed by primary care residents and faculty. The clinics attracted a substantial portion of each department's faculty and residents. The clinics united primary care providers from different departments as a stronger, more unified voice in negotiating with the hospital and in fostering needed changes for primary care in the institution. Interdisciplinary teams require considerable time and labor both in planning (because of joint decision making) and in operation. Better staff structures and staff development must be learned through trial and error because there are not established benchmarks for interdisciplinary teams. Governance presents problems, primarily because loyalties to departments may supersede those to the clinic practice, and sometimes the departments' teaching priorities are challenged by clinic directors' need to ensure filling their interdisciplinary staff needs. These obstacles to collaboration can be addressed creatively, and ultimately the comprehensiveness and quality of care convinces providers and the institution.

Academic Medical Centers↗
PubMed1998

Synthesis and Characterization of Molybdenum Based Colloidal Particles.

The synthesis and characterization of molybdenum colloidal particles were evaluated using thermal and sonochemical methods and starting from different metal precursors, Mo(CO)6 and (NH4)2MoS4. The products were characterized by elemental analysis, spectroscopic (UV, FTIR), and surface analysis (XPS) techniques, as well as by transmission electron microscopy (TEM) for determining the particle sizes. Using Mo(CO)6 as metal source, particle sizes with an average diameter of 1.5 nm can be obtained using tert-amyl alcohol as solvent and tetrahydrothiophene as sulfurating ligand. The characterization of these particles showed that they are composed of molybdenum oxide MoO3. Using (NH4)2MoS4 as metal precursor, particles with average diameters of 4.7 and 2.5 nm were synthesized using thermal and sonochemical methods, respectively. The characterization of these particles showed them to be composed of molybdenum sulfide, MoS2. The sonochemical method proved to be the fastest and most convenient synthetic pathway of obtaining small colloidal particles at low temperatures and with control of the average size. Copyright 1998 Academic Press.

Journal Article↗
PubMed1996

Fostering the health of communities: a unifying mission for the University of New Mexico Health Sciences Center.

Fostering the health of communities can serve as a unifying mission of the academic health center (AHC), which can set the AHC apart from other health providers in the community. To achieve this mission, the University of New Mexico's AHC is increasingly focusing education, research, and service upon the identified health and service needs of communities in its state. Since major health problems in our society have social, behavioral, and economic roots, New Mexico's AHC has tapped into the broad expertise of its different components as well as that of its state and community partners to adequately address health problems in the community. Its hospitals offer financing and management resources, its colleges offer innovative approaches to community-based education, and the state department of health offers expertise in health policy development. To adequately respond to the complexity of community health needs, the different colleges and departments at New Mexico's AHC are increasingly merging into integrated governance units. Measures of community outreach success include evidence of strengthened community development, increased health care access, and improved indices of community health. New Mexico's AHC formed an interdisciplinary rural outreach task force, which has demonstrated its ability to form partnerships with state and local agencies and to mobilize institutional resources in education, research, and service from the AHC's different departments, colleges, and hospitals to respond promptly to unique community health needs. Evidence shows that such an integrated, coordinated AHC intervention can generate strong and lasting AHC-community alliances, improve the quality and economic viability of community health systems, and enhance the financial resources of the AHC.

Academic Medical Centers↗
PubMed1994

Innovative generalist programs: academic health care centers respond to the shortage of generalist physicians.

Academic health care centers increasingly are exploring innovative ways to increase the supply of generalist physicians. The authors review successful innovations at representative academic health centers in the areas of recruitment and admissions, undergraduate medical education, residency training, and practice support. Lessons learned focus on those areas that have demonstrated improvements in the number and quality of physicians trained in family practice, general pediatrics, and general internal medicine. Successful recruitment of generalism-oriented applicants requires identification and tracking of rural, minority, and other special groups of students at the high school and college levels. Academic health care centers that provide early, sustained, community-based, ambulatory experiences for medical students and residents encourage trainees to maintain and choose generalist careers. Finally, academic health care centers that link with community providers and with state government encourage the retention of generalist physicians through continuing education and teaching networks.

Academic Medical Centers↗
PubMed1990

Comparison of reactogenicity and antigenicity of M37 rotavirus vaccine and rhesus-rotavirus-based quadrivalent vaccine.

90 Venezuelan infants aged 10-20 weeks were randomly allocated to four groups which received one of the following: the M37 vaccine (1 x 10(4) pfu [plaque-forming units]); quadrivalent rotavirus vaccine (1 x 10(4) pfu each of serotype 3 rhesus rotavirus [RRV] and human rotavirus-RRV reassortants of serotypes 1, 2, and 4); balanced quadrivalent vaccine consisting of 1 x 10(4) pfu of serotype 1 and 3 components but 5 x 10(4) pfu of serotype 2 and 4 components; or placebo. The frequencies of transient febrile responses in these four groups were 20%, 27%, 30%, and 9%. 50% of 22 infants tested who received M37 vaccine showed a serum rotavirus IgA antibody response, compared with 74% of the 23 quadrivalent and 86% of the 22 balanced-quadrivalent recipients. 64% of the M37 recipients showed a neutralising antibody response to M37; 27% showed such responses to human serotype 1 Wa strain and 27% to serotype 4 neonatal strain ST3. 17-39% of the quadrivalent recipients and 27-41% of the balanced-quadrivalent recipients showed neutralising antibody responses to serotypes 1-4. 70-73% of the quadrivalent and balanced quadrivalent groups also showed neutralising antibody responses to RRV.

Antibodies, Viral↗