Nanomechanical Pyrolytic Carbon Resonators: Novel Fabrication Method and Characterization of Mechanical Properties

Micro- and nanomechanical string resonators, which essentially are highly stressed bridges, are of particular interest for micro- and nanomechanical sensing because they exhibit resonant behavior with exceptionally high quality factors. Here, we fabricated and characterized nanomechanical pyrolytic carbon resonators (strings and cantilevers) obtained through pyrolysis of photoresist precursors. The developed fabrication process consists of only three processing steps: photolithography, dry etching and pyrolysis. Two different fabrication strategies with two different photoresists, namely SU-8 2005 (negative) and AZ 5214e (positive), were compared. The resonant behavior of the pyrolytic resonators was characterized at room temperature and in high vacuum using a laser Doppler vibrometer. The experimental data was used to estimate the Young’s modulus of pyrolytic carbon and the tensile stress in the string resonators. The Young’s moduli were calculated to be 74 ± 8 GPa with SU-8 and 115 ± 8 GPa with AZ 5214e as the precursor. The tensile stress in the string resonators was 33 ± 7 MPa with AZ 5214e as the precursor. The string resonators displayed maximal quality factor values of up to 3000 for 525-µm-long structures

Field-induced breakdown of the quantum Hall effect

A numerical analysis is made of the breakdown of the quantum Hall effect caused by the Hall electric field in competition with disorder. It turns out that in the regime of dense impurities, in particular, the number of localized states decreases exponentially with the Hall field, with its dependence on the magnetic and electric field summarized in a simple scaling law. The physical picture underlying the scaling law is clarified. This intra-subband process, the competition of the Hall field with disorder, leads to critical breakdown fields of magnitude of a few hundred V/cm, consistent with observations, and accounts for their magnetic-field dependence \propto B^{3/2} observed experimentally. Some testable consequences of the scaling law are discussed.Comment: 7 pages, Revtex, 3 figures, to appear in Phys. Rev.

Electronic Processes at the Breakdown of the Quantum Hall Effect

Microscopic processes giving the energy gain and loss of a two-dimensional electron system in long-range potential fluctuations are studied theoretically at the breakdown of the quantum Hall effect in the case of even-integer filling factors. The Coulomb scattering within a broadened Landau level is proposed to give the gain, while the phonon scattering to give the loss. The energy balance equation shows that the electron temperature T_e and the diagonal conductivity sigma_{xx} exhibit a bistability above the lower critical electric field E_{c1}. Calculated values of E_{c1} as well as T_e and sigma_{xx} at E_{c1} are in agreement with the observed values in their orders of magnitude.Comment: 4 pages, 2 Postscript figures, submitted to the Journal of the Physical Society of Japa

Associations between adherence, depressive symptoms and health-related quality of life in young adults with cystic fibrosis

BACKGROUND: Cystic fibrosis (CF) is a life shortening disease, however prognosis has improved and the adult population is growing. Most adults with cystic fibrosis live independent lives and balance the demands of work and family life with a significant treatment burden. The aim of this study was to examine the relationships among treatment adherence, symptoms of depression and health-related quality of life (HRQoL) in a population of young adults with CF. METHODS: We administered three standardized questionnaires to 67 patients with CF aged 18–30 years; Morisky Medication Adherence Scale, Major Depression Inventory, and Cystic Fibrosis Questionnaire-Revised. RESULTS: There was a response rate of 77 % and a majority of the young adults (84 %) were employed or in an education program. Most participants (74 %) reported low adherence to medications. One third (32.8 %) of the participants reported symptoms of depression. HRQoL scores were especially low on Vitality and Treatment Burden, and symptoms of depression were associated with low HRQoL scores (p < 0.01) with medium to large deficits across on all HRQoL domains (Cohen’s d 0.60–1.72) except for the domain treatment burden. High depression symptom scores were associated with low adherence (r = −0.412, p < 0.001). CONCLUSIONS: Despite improved physical health, many patients with CF report poor adherence, as well as impaired mental wellbeing and HRQoL. Thus, more attention to mental health issues is needed

Postoperative serum CA19-9, YKL-40, CRP and IL-6 in combination with CEA as prognostic markers for recurrence and survival in colorectal cancer

Background In colorectal cancer (CRC) patients, guidelines only recommend measurement of preoperative carcinoembryonic antigen (CEA), although postoperative CEA may be more informative. However, the sensitivity of both preoperative and postoperative CEA in identifying relapse is limited. We studied whether CA19-9, YKL-40, C-reactive protein (CRP) and interleukin (IL)-6 add prognostic information combined with postoperative CEA. Material and methods This post-hoc analysis included 147 radically resected stage II (n = 38), III (n = 91) and IV (n = 18) CRC patients treated with adjuvant 5-fluorouracil (5-FU)-based therapy in the phase III LIPSYT study (ISRCTN98405441). We collected postoperative blood samples a median of 48 days after surgery. We analysed relapses, sensitivity, positive predictive value (PPV) and disease-free (DFS) and overall survival (OS) by bootstrap, Kaplan-Meier and adjusted Cox-models in the elevated vs. normal biomarker groups. Results Elevated postoperative CEA associated with impaired DFS (HR 7.23; CI(95%)3.85-13.58), impaired OS (HR 7.16; CI(95%)3.76-13.63), and more relapses (HR 7.9; CI(95%)3.4-18.2); but sensitivity for CEA in finding relapses was only 31% (CI(95%)21-48%). Normal CEA combined with an elevated YKL-40 or elevated CRP showed more relapses (HR for YKL-40 2.13 [CI(95%)1.10-4.13], HR for CRP 3.14 [CI(95%)1.21-8.16]), impaired DFS (HR 2.18 [CI(95%)1.12-4.24] or 3.23 [CI(95%)1.34-7.82]), and impaired OS (2.33 [CI(95%)1.24-4.40] or 2.68 [CI(95%)1.12-6.44]). Elevated CEA combined with a concomitantly elevated CA19-9, YKL-40, CRP or IL-6 showed a respective PPV of 100, 90, 100, and 100%. Conclusion In radically operated stage II to IV CRC patients who received adjuvant 5-FU-based chemotherapy, a postoperatively elevated CEA alone or in combination with CA19-9, YKL-40, CRP, or IL-6, or a normal CEA combined with an elevated YKL-40 or with an elevated CRP, may indicate patients at high risk of relapse.Peer reviewe

A study of 15N14N isotopic exchange over cobalt molybdenum nitrides

The 14N/15N isotopic exchange pathways over Co3Mo3N, a material of interest as an ammonia synthesis catalyst and for the development of nitrogen transfer reactions, have been investigated. Both the homomolecular and heterolytic exchange processes have been studied, and it has been shown that lattice nitrogen species are exchangeable. The exchange behavior was found to be a strong function of pretreatment with ca. 25% of lattice N atoms being exchanged after 40 min at 600 °C after N2 pretreatment at 700 °C compared to only 6% following similar Ar pretreatment. This observation, for which the potential contribution of adsorbed N species can be discounted, is significant in terms of the application of this material. In the case of the Co6Mo6N phase, regeneration to Co3Mo3N under 15N2 at 600 °C occurs concurrently with 14N15N formation. These observations demonstrate the reactivity of nitrogen in the Co–Mo–N system to be a strong function of pretreatment and worthy of further consideration

Hydrodynamic Equation for the Breakdown of the Quantum Hall Effect in a Uniform Current

The hydrodynamic equation for the spatial and temporal evolution of the electron temperature T_e in the breakdown of the quantum Hall effect at even-integer filling factors in a uniform current density j is derived from the Boltzmann-type equation, which takes into account electron-electron and electron-phonon scatterings. The derived equation has a drift term, which is proportional to j and to the first spatial derivative of T_e. Applied to the spatial evolution of T_e in a sample with an abrupt change of the width along the current direction, the equation gives a distinct dependence on the current direction as well as a critical relaxation, in agreement with the recent experiments.Comment: 4 pages, 1 Postscript figure, corrected equations, to be published in J. Phys. Soc. Jpn. 70 (2001) No.