1,455 research outputs found
Sub-50 nm period patterns with EUV interference lithography
No full textWe have used transmission diffraction gratings in an interferometric setup to pattern one- and two dimensional periodic patterns with periods near 50 nm. The diffraction gratings were written with e-beam lithography. The exposures were made at 13.4 nm wavelength with undulator radiation, which provides spatially coherent radiation. This technique offered a multiplication of pattern frequency by a factor of 2 and root2 in the one- and two-dimensional cases, respectively. Interference lithography with gratings offers a number of advantages, including achromaticity and insensitivity to misalignment. The demonstrated structures include line/space patterns with 45 nm period and a square array of holes with 56 nm period. (C) 2003 Elsevier Science B.V. All rights reserved.The authors thank B. Haas and S. Stutz for help with preparation of the diffraction grating masks
Directed self-assembly of block copolymer blends into nonregular device-oriented structures
No full textEpitaxial self-assembly of block copolymers on lithographically defined nanopatterned substrates
No full textParallel processes for patterning densely packed nanometre- scale structures are critical for many diverse areas of nanotechnology. ;Thin films of diblock copolymers(1-11) can self-assemble into ordered periodic structures at the molecular scale (similar to5 to 50 nm), and have been used as templates to fabricate quantum dots(1,2), nanowires(3-5), magnetic storage media(6), nanopores(7) and silicon capacitors(8). Unfortunately, perfect periodic domain ordering can only be achieved over micrometre-scale areas at best(12,13) and defects exist at the edges of grain boundaries. These limitations preclude the use of block-copolymer lithography for many advanced applications(14). Graphoepitaxy(12,15), in-plane electric fields(3,16), temperature gradients(17), and directional solidification(14,18) have also been demonstrated to induce orientation or long-range order with varying degrees of success. Here we demonstrate the integration of thin films of block copolymer with advanced lithographic techniques to induce epitaxial self-assembly of domains. The resulting patterns are defect-free, are oriented and registered with the underlying substrate and can be created over arbitrarily large areas. These structures are determined by the size and quality of the lithographically defined surface pattern rather than by the inherent limitations of the self-assembly process. Our results illustrate how hybrid strategies to nanofabrication allow for molecular level control in existing manufacturing processes.We thank F. Cerrina, E. W. Edwards and S. Xiao for discussions, and
V. Golovkina and J. Wallace for assistance with the EUV-IL system. This work was supported by
the Semiconductor Research Corporation, the National Science Foundation through the
Materials Research Science and Engineering Center, and the Camille Dreyfus Teacher-Scholar
Award. S.K. acknowledges a research fellowship from the Post-Doctoral Fellowship Program of
the Korea Science and Engineering Foundation. Facilities and staff of the CNTech were supported
by DARPA and the Intel Corporation, and the Synchrotron Radiation Center is supported by the
National Science Foundation
Contextual metrical invisibility
No full textIn some languages, certain vowels are invisible to syllable-sensitive processes, but only in certain contexts. This paper argues that metrically invisible vowels are undominated by a syllable node in prosodic structure. Considering mainly Mohawk and Passamaquoddy, the behavior of these "weak vowels" is derived from pressure to avoid using weak vowels as syllable nuclei, countered by pressure to realize underlying segments in well-formed syllables. Because not only epenthetic vowels can be weak vowels, their unsuitability as syllable nuclei is derived representationally, through amount of underlying prosodic structure. Existing analyses of the data are critiqued, and the theoretical implications and potential extensions are discussed.The definitive version of this paper was published in PF: Papers at the Interface (1997) and is available at http://mitwpl.mit.edu/catalog/mwpl30/Hagstrom, P. (1997). Contextual metrical invisibility. In B. Bruening, Y. Kang, & M. McGinnis (Eds.) PF: Papers at the interface (pp. 113-181). Cambridge, MA: Department of Linguistics and Philosophy, Massachusetts Institute of Technology
The portraits of the female author: the case of Ángela Figuera Aymerich
No full textEste artículo se enmarca en el Programa Severo Ochoa (referencia PA-17-PF-BP16126) de Ayudas predoctorales para la investigación y la docencia del Gobierno del Principado de Asturias
The prosodic structure of Serbo-Croatian function words: An argument for tied constraints
No full textThe question of the proper treatment of clitics has received considerable attention in literature on the syntax-morphology and morphology-phonology interfaces. Selkirk (1996) proposes an elegant theory of the prosodification of clitic function words crosslinguistically, demonstrating that variation in the behavior of function words both within a language (English) and across dialects of a language (Serbo-Croatian) follows straightforwardly from re-rankings of universal constraints in an Optimality Theory. In this paper I argue that, in addition to strict re-rankings of constraints, tied constraints are also needed within such a system, in order to capture the Serbo-Croatian facts. I discuss three empirical shortcomings of Selkirk¹s analysis, all involving optionality, and show how they can be remedied by appealing to a particular notion of what it means for constraints to be tied in rank. To the extent that Selkirk¹s basic insights are correct, this supports the conclusion that tied constraints play an important role in OT accounts of the ways in which dependent and independent morphemes are combined into larger prosodic units. It adds to the growing evidence for "crucial nonranking", whereby separate tableaux are computed for each ordering of the relevant constraints and the output of each is a valid possibility in the language.The definitive version of this paper was published in MITWPL 30: PF: Papers at the Interface (1997) and is available at http://mitwpl.mit.edu/catalog/mwpl30/Schütze, C.T. (1997). The Prosodic Structure of Serbo-Croatian Function Words: An Argument for Tied Constraints. In B. Bruening, Y. Kang, & M. McGinnis (Eds.) PF: Papers at the Interface. Cambridge, MA : MIT Dept. of Linguistics
Stochastic Nodal Analysis: EnKF and PF applied to petroleum production systems
No full textA petroleum production system is generally modelled based on the concept of nodal analysis, where the entire system is broken down into discrete elements such as near-well bore, tubing, surface choke and flow line. Operating flow rates and pressures can be estimated with a nodal analysis procedure by calculation of the intersection of performance curves. Input parameters in nodal analysis of production systems are considered deterministic, however, some of these parameters are better represented as distributions. In this report, the ensemble-based data assimilation methods “ensemble Kalman filter” (EnKF) and “particle filter” (PF) are applied to steady-state models of a production system for tuning of uncertain model parameters during the test separator phase. The performance of the EnKF and the PF is tested with the use of twin experiments. The calibrated model parameters of the choke, tubing and the near-well bore elements with EnKF and PF can be used to create an ensemble of performance curves leading to an ensemble of operating flow rates and pressures. The foreseen next step is to use the posterior distributions of model parameters as inputs for soft sensing of flow rates during semi-steady-state production for a single phase oil reservoir, where the oil rate and reservoir pressure are considered as unknown parameters. In the twin experiments as used in this thesis, a total number of three steady-state pressure drop measurements was used to estimate a total of six independent parameters which constitutes an ill-posed problem, resulting in non-unique parameter estimates. It is recommended to alleviate this issue by either reducing the number of parameters or by using multiple separator tests at different flow rates.Petroleum Engineering and Geo-science
PI3K/mTOR Dual Inhibitor PF-04691502 Is a Schedule-Dependent Radiosensitizer for Gastroenteropancreatic Neuroendocrine Tumors
No full textPatients with advanced-stage gastroenteropancreatic neuroendocrine tumors (GEP-NETs) have a poor overall prognosis despite chemotherapy and radiotherapy (e.g., peptide receptor radionuclide therapy (PRRT)). Better treatment options are needed to improve disease regression and patient survival. The purpose of this study was to examine a new treatment strategy by combining PI3K/mTOR dual inhibition and radiotherapy. First, we assessed the efficacy of two PI3K/mTOR dual inhibitors, PF-04691502 and PKI-402, to inhibit pAkt and increase apoptosis in NET cell lines (BON and QGP-1) and patient-derived tumor spheroids as single agents or combined with radiotherapy (XRT). Treatment with PF-04691502 decreased pAkt (Ser473) expression for up to 72 h compared with the control; in contrast, decreased pAkt expression was noted for less than 24 h with PKI-402. Simultaneous treatment with PF-04691502 and XRT did not induce apoptosis in NET cells; however, the addition of PF-04691502 48 h after XRT significantly increased apoptosis compared to PF-04691502 or XRT treatment alone. Our results demonstrate that schedule-dependent administration of a PI3K/mTOR inhibitor, combined with XRT, can enhance cytotoxicity by promoting the radiosensitivity of NET cells. Moreover, our findings suggest that radiotherapy, in combination with timed PI3K/mTOR inhibition, may be a promising therapeutic regimen for patients with GEP-NET
LASER SPECTROSCOPY OF THE STATE
No full text A.E. Douglas, M. Frackoviak, Can. J. Phys. 40, 832 (1962)Author Institution: Department of Chemistry, Kansas State UniversitySpectra of the PF bands were recorded using laser excitation spectroscopy. The PF molecules in the ground electronic state were produced by passing a mixture through a microwave discharge in a flow reactor at room temperature. The obtained spectroscopic constants are consistent with the earlier results of Douglas and for . The strong dependence of the lambda doubling in the state on the vibrational quantum number and irregular spacing of the vibrational energies indicate interactions with the and another state. The dipole function of the A-X transition was calculated from the radiative lifetimes and dispersed fluorescence spectra
Cyanophage Pf-WMP4, a T7-like phage infecting the freshwater cyanobacterium Phormidium foveolarum: Complete genome sequence and DNA translocation
No full textAbstractWe report the complete 40,938-bp genome sequence of a cyanophage, Pf-WMP4, which infects the freshwater cyanobacterium Phormidium foveolarum Gom. Nine of the forty-five potential open reading frames in the Pf-WMP4 genome share similarities with the genes found in T7-like phages. Using in vitro transcription, we found that seven promoters at the leftmost end of the genome can be recognized by the host RNA polymerase. By blocking transcriptional and translational inhibitors, we found that Pf-WMP4 DNA translocation, with an average translocation rate of 19.8±2.7 bp s−1 at 28 °C, requires both host transcription and protein synthesis of an unknown factor. Therefore the mechanism of cyanophage Pf-WMP4 DNA injection may be driven both by a T7-like internalization mechanism as well as an additional unknown mechanism requiring de novo protein synthesis. Our analysis of the Pf-WMP4 genome sheds new light on the translocation strategies and evolutionary traces of phages belonging to the T7 supergroup
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