Biomedical subjects

P Delsing

Publications and source records attributed to P Delsing.

At least 19 recordsLinked to original sources

PubMed2005

Observation of quantum capacitance in the Cooper-pair transistor.

We have fabricated a Cooper-pair transistor (CPT) with parameters such that for appropriate voltage biases, it behaves essentially like a single Cooper-pair box (SCB). The effective capacitance of a SCB can be defined as the derivative of the induced charge with respect to gate voltage and has two parts, the geometric capacitance, C(geom), and the quantum capacitance C(Q). The latter is due to the level anticrossing caused by the Josephson coupling and is dual to the Josephson inductance. It depends parametrically on the gate voltage and its magnitude may be substantially larger than C(geom). We have detected C(Q) in our CPT, by measuring the in phase and quadrature rf signal reflected from a resonant circuit in which the CPT is embedded. C(Q) can be used as the basis of a charge qubit readout by placing a Cooper-pair box in such a resonant circuit.

Journal Article↗

PubMed2005

Collapse of thermal activation in moderately damped Josephson junctions.

We study switching current statistics in moderately damped Nb-InAs-Nb and intrinsic Bi2Sr2CaCu2O8+delta) Josephson junctions. A paradoxical collapse of thermal activation with increasing temperature is reported and explained by the interplay of two conflicting consequences of thermal fluctuations, which can both assist in premature escape and help in retrapping back into the stationary state. We analyze the influence of dissipation on the thermal escape by tuning damping with a gate voltage, magnetic field, temperature, and an in situ capacitor.

Journal Article↗

PubMed2005

Macroscopic quantum tunneling in d-wave YBa2Cu3O7-delta Josephson junctions.

The escape rate from the zero voltage state in a superconducting Josephson junction (JJ) is determined by the temperature, but it saturates at low temperature due to macroscopic quantum tunneling (MQT). Complications due to d-wave symmetry in a high temperature superconductor, like low energy quasiparticles and an unconventional current-phase relation, may influence the escape rate. We report, for the first time to our knowledge, the observation of MQT in a YBa(2)Cu(3)O(7-delta) grain boundary biepitaxial JJ. This proves that dissipation can be significantly reduced by a proper junction configuration, which is of significance for quantum coherence.

Journal Article↗

PubMed2003

Quantum charge fluctuations and the polarizability of the single-electron box.

We measure the average charge on the island of a single-electron box, with an accuracy of two thousandths of an electron. Thermal fluctuations alone cannot account for the dependence of the average charge on temperature, on external potential, or on the quasiparticle density of states in the metal from which the box is formed. In contrast, we find excellent agreement between these measurements and a theory that treats the quantum fluctuations of charge perturbatively.

Journal Article↗

PubMed2003

Measurement of the excited-state lifetime of a microelectronic circuit.

We demonstrate that a continuously measured microelectronic circuit, the Cooper-pair box measured by a radio-frequency single-electron transistor, approximates a quantum two-level system. We extract the Hamiltonian of the circuit through resonant spectroscopy and measure the excited-state lifetime. The lifetime is more than 10(5) times longer than the inverse transition frequency of the two-level system, even though the measurement is active. This lifetime is also comparable to an estimate of the known upper limit, set by spontaneous emission, for this circuit.

Journal Article↗

PubMed2001

Radio-frequency single-electron transistor as readout device for qubits: charge sensitivity and backaction.

We study the radio-frequency single-electron transistor (rf-SET) as a readout device for charge qubits. We measure the charge sensitivity of an rf-SET to be 6.3microe/sqrt[Hz] and evaluate the backaction of the rf-SET on a single Cooper-pair box. This allows us to compare the needed measurement time with the mixing time of the qubit imposed by the measurement. We find that the mixing time can be substantially longer than the measurement time, which would allow readout of the state of the qubit in a single shot measurement.

Journal Article↗

PubMed2001

Experimental evidence of one-dimensional plasma modes in superconducting thin wires.

We have studied niobium superconducting thin wires deposited onto a SrTiO3 substrate. By measuring the reflection coefficient of the wires, resonances are observed in the superconducting state in the 130 MHz to 4 GHz range. They are interpreted as standing wave resonances of one-dimensional plasma modes propagating along the superconducting wire. The experimental dispersion law, omega versus q, presents a linear dependence over the entire wave vector range. The modes are softened as the temperature increases close the superconducting transition temperature. Very good agreement is obtained between our data and the predicted dispersion relation of one-dimensional plasma modes.

Journal Article↗

PubMed2001

Preferences for treatment during a first psychotic episode.

Psychiatric services providing care for patients and their families confronted with a first psychotic episode need to be sensitive towards patients' and families' preferences. Ten patients, ten family members and ten professional caregivers composed a list of 42 preferences in the treatment for a first psychotic episode. In total 99 patients, 100 family members and 263 professional caregivers evaluated these preferences, thus producing an order of priorities. There appears to be considerable agreement among the groups of respondents regarding their top ten priorities, especially concerning information on diagnosis and medication. However, we found important differences between groups of respondents. The results suggest that in psychiatric services great attention should be given to psycho-education and early outpatient intervention.

Adult↗

PubMed2000

Current mirror effect and correlated cooper-pair transport in coupled arrays of small Josephson junctions.

We have measured the transport properties of capacitively coupled one-dimensional arrays of small aluminum Josephson junctions. Under suitable biasing conditions, the samples act as current mirrors; the currents in the two arrays couple to each other and become equally large. The coupling is found both for currents flowing in the same direction and in opposite directions. We have also measured the time dependent fluctuations of the currents in the two arrays, and we find a strong correlation or anticorrelation of the fluctuations depending on the relative direction of the two currents.

Journal Article↗

PubMed2000

Evidence for coexistence of the superconducting gap and the pseudogap in Bi-2212 from intrinsic tunneling spectroscopy.

We present intrinsic tunneling spectroscopy measurements on small Bi2Sr2CaCu2O8+x mesas. The tunnel conductance curves show both sharp peaks at the superconducting gap voltage and broad humps representing the c-axis pseudogap. The superconducting gap vanishes at Tc, while the pseudogap exists both above and below Tc. Our observation implies that the superconducting and pseudogaps represent different coexisting phenomena.

Journal Article↗

PubMed2000

Morphological changes following experimental intraventricular haemorrhage and intraventricular fibrinolytic treatment with recombinant tissue plasminogen activator.

Intraventricular haemorrhage (IVH) occurs in up to 50% of patients with primary intracerebral haemorrhage and aneurysmal subarachnoid haemorrhage. It is a significant and independent contributor to mortality and morbidity in these intracranial haemorrhages. Using a model of isolated IVH, we assessed the morphological changes induced by intraventricular bleeding and investigated the effects of intraventricular fibrinolytic treatment following IVH. IVH was induced in 32 pigs by intraventricular infusion of 10 ml autologous blood along with thrombin. The treatment group received an intraventricular injection of 1.5 mg (1 mg/ml) tissue plasminogen activator (tPA) following the injection of blood. The placebo group received the same volume of normal saline. Morphological examinations of the brains were carried out 7 days and 6 weeks following IVH. The ventricles were incompletely filled with blood and significantly enlarged in the placebo group 7 days after the IVH. In contrast, no residual intraventricular clots were visible in the animals treated with tPA, and the diameters of the lateral ventricles had returned to normal within 7 days. Marked losses of the ependymal covering of the ventricular walls were found in the placebo-treated animals, while the ependymal layer was largely intact in the animals treated with tPA. No haemorrhages induced by tPA were observed. The results indicate that intraventricularly administered tPA significantly enhances the lysis of intraventricular blood clots, accelerates the resolution of acute posthaemorrhagic hydrocephalus, and preserves the integrity of the ependymal layer.

Animals↗

PubMed1998

The radio-frequency single-electron transistor (RF-SET): A fast and ultrasensitive electrometer

A new type of electrometer is described that uses a single-electron transistor (SET) and that allows large operating speeds and extremely high charge sensitivity. The SET readout was accomplished by measuring the damping of a 1.7-gigahertz resonant circuit in which the device is embedded, and in some ways is the electrostatic "dual" of the well-known radio-frequency superconducting quantum interference device. The device is more than two orders of magnitude faster than previous single-electron devices, with a constant gain from dc to greater than 100 megahertz. For a still-unoptimized device, a charge sensitivity of 1.2 x 10(-5) e/hertz was obtained at a frequency of 1.1 megahertz, which is about an order of magnitude better than a typical, 1/f-noise-limited SET, and corresponds to an energy sensitivity (in joules per hertz) of about 41 Planck's over 2pi.

Journal Article↗

PubMed1997

Ventricular dilatation in experimental intraventricular hemorrhage in pigs. Characterization of cerebrospinal fluid dynamics and the effects of fibrinolytic treatment.

BACKGROUND AND PURPOSE: Hemorrhagic ventricular dilatation (HVD) is a prominent feature of human intraventricular hemorrhage (IVH) and a strong indicator for poor outcome. We developed an IVH model to define the mechanisms responsible for HVD and to test the efficacy of intraventricular administration of tissue plasminogen activator (TPA) in the treatment of HVD. METHODS: Isolated IVH was produced in pigs by injecting 10 mL of blood simultaneously with thrombin into the right lateral ventricle. The treatment group received 1.5 mg of TPA after induction of IVH. Intraventricular blood volume and the volume of the lateral ventricles were assessed by CT after 90 minutes, 7 days, and 42 days. Intracranial pressure, the pressure-volume index, and the resistance to outflow of cerebrospinal fluid (R(out)) were measured 30 minutes and 7 days after IVH. RESULTS: After IVH, the volume of the lateral ventricles increased from 1.98 +/- 0.69 to 6.43 +/- 1.23 mL (P < .001). There was a linear relationship between ventricular and clot volume (P = .014). Initially, R(out) increased from 24.34 +/- 7.13 to 63.56 +/- 64.91 mm Hg/mL per minute (P < .001). After 7 days, restoration of normal cerebrospinal fluid circulation occurred, but the ventricles were still significantly enlarged (5.24 +/- 1.76 mL, P < .001) and filled with blood. Within 6 weeks, ventricular volume had returned to normal values, paralleled by complete clot resolution. Intraventricular administration of TPA significantly accelerated clot clearance and restoration of normal ventricle volume. CONCLUSIONS: These results suggest that intraventricular bleeding may cause impairment of cerebrospinal fluid circulation but that the mass effect of clots distending the ventricle walls is the most important mechanism responsible for HVD. This model closely imitates several prominent features of human IVH and may therefore be a useful tool for preclinical assessment of the efficacy and safety of treatment with TPA.

Animals↗

PubMed1996