1,029 research outputs found
Electric field distortions in structures of the twist bend nematic (NTB) phase of a bent-core liquid crystal
Dielectric spectroscopy of a twist bend nematic phase of an achiral bent core
liquid crystalline compound under DC bias is used to investigate its response
to electric field. Two collective relaxation processes are revealed, these are
assigned to distortions of helicoidal structure by the external bias field.
Frequency of the mode depends primarily on the helicoidal angle and has
anomalous, softening- like behaviour at the nematic to the twist bend nematic
transition. A coupling of dielectric anisotropy with electric field gives rise
to a new equilibrium periodic structure in the time scale involved. The modulus
of the wave vector gradually vanishes on increasing the bias field (except for
the initial behaviour, which is just the opposite). Transition from the twist
bend to the splay bend structure is clearly observed by a sudden drop in the
frequency of this mode, which decreases almost linearly with increasing field.
Results agree with predictions from current models for the periodically
distorted a twist bend nematic phase.Comment: 14 PAGES, 7 FIGURES, submitted to Physical Review Letter
The equivalence of four extensions of context-free grammars
There is currently considerable interest among computational linguists in grammatical formalisms with highly restricted generative power. This paper concerns the relationship between the class of string languages generated by several such formalisms, namely, combinatory categorial grammars, head grammars, linear indexed grammars, and tree adjoining grammars. Each of these formalisms is known to generate a larger class of languages than context-free grammars. The four formalisms under consideration were developed independently and appear superficially to be quite different from one another. The result presented in this paper is that all four of the formalisms under consideration generate exactly the same class of string languages
Caring for the collective: biopower and agential subjectification in wildlife conservation
types: ArticleCopyright © 2014 PionPost Print. Srinivasan, K. 2014. The definitive, peer-reviewed and edited version of this article is published in Environment and Planning D: Society and Space, Vol. 32, Issue 3, pp. 501 – 517 DOI:10.1068/d13101pThis paper explores turtle conservation in Odisha, India, to map the complicated ways in which animal well-being is pursued in the contemporary world. Using insights from Foucault’s work on biopolitics, it offers an account of conservation as population politics, questioning the entanglement of harm and care that infuses this space of more-than-human social change. In doing this, the paper elaborates the concept of agential subjectification in order to track the mechanisms that underlie the asymmetric circulation of biopower in human–animal interactions and to develop Foucauldian scholarship for the examination of present-day manifestations of the ‘will to improve’.RGS‑IBGCulture and Animals Foundatio
Linear iterated pushdowns
This paper discusses variants of nondeterministic one-way S-automata and context-free S-grammars where S is a storage type. The framework that these systems provide can be used to give alternative formulations of embedded pushdown automata and linear indexed grammars. The embedded pushdown automata is obtained by means of a linear version of a class of storage types called iterated pushdowns. Linear indexed grammar is obtained by using the pushdown storage type and restricting the way in which the grammar uses its storage
Shelter from the storm? Use and misuse of coastal vegetation bioshields for managing natural disasters
Vegetated coastal ecosystems are known to provide myriad ecosystem services to billions of people globally. However, in the aftermath of a series of recent natural disasters, including the Indian Ocean Tsunami, Hurricane Katrina and Cyclone Nargis, coastal vegetation has been singularly promoted as a protection measure against large storm surges and tsunami. In this paper, we review the use of coastal vegetation as a "bioshield" against these extreme events. Our objective is to investigate the long-term consequences of rapid plantation of bioshields on local biodiversity and human capital. We begin with an overview of the scientific literature, in particular focusing on studies published since the Indian Ocean Tsunami in 2004 and discuss the science of wave attenuation by vegetation. We then explore case studies from the Indian subcontinent and evaluate the detrimental impacts bioshield plantations can have upon native ecosystems. We draw a clear distinction between coastal restoration and the introduction of exotic species in inappropriate locations in the name of coastal protection. We conclude by placing existing bioshield policies into a larger socio-political context and outline a new direction for coastal vegetation policy and research
Trapping dust particles in the outer regions of protoplanetary disks
In order to explain grain growth to mm sized particles and their retention in
outer regions of protoplanetary disks, as it is observed at sub-mm and mm
wavelengths, we investigate if strong inhomogeneities in the gas density
profiles can slow down excessive radial drift and can help dust particles to
grow. We use coagulation/fragmentation and disk-structure models, to simulate
the evolution of dust in a bumpy surface density profile which we mimic with a
sinusoidal disturbance. For different values of the amplitude and length scale
of the bumps, we investigate the ability of this model to produce and retain
large particles on million years time scales. In addition, we introduced a
comparison between the pressure inhomogeneities considered in this work and the
pressure profiles that come from magnetorotational instability. Using the
Common Astronomy Software Applications ALMA simulator, we study if there are
observational signatures of these pressure inhomogeneities that can be seen
with ALMA. We present the favorable conditions to trap dust particles and the
corresponding calculations predicting the spectral slope in the mm-wavelength
range, to compare with current observations. Finally we present simulated
images using different antenna configurations of ALMA at different frequencies,
to show that the ring structures will be detectable at the distances of the
Taurus Auriga or Ophiucus star forming regions.Comment: Pages 15, Figures 14. Accepted for publication in Astronomy and
Astrophysic
Dose-finding study of a 90-day contraceptive vaginal ring releasing estradiol and segesterone acetate.
ObjectiveTo evaluate serum estradiol (E2) concentrations during use of 90-day contraceptive vaginal rings releasing E2 75, 100, or 200 mcg/day and segesterone acetate (SA) 200 mcg/day to identify a dose that avoids hypoestrogenism.Study designWe conducted a multicenter dose-finding study in healthy, reproductive-aged women with regular cycles with sequential enrollment to increasing E2 dose groups. We evaluated serum E2 concentrations twice weekly for the primary outcome of median E2 concentrations throughout initial 30-day use (target ≥40 pg/mL). In an optional 2-cycle extension substudy, we randomized participants to 2- or 4-day ring-free intervals per 30-day cycle to evaluate bleeding and spotting based on daily diary information.ResultsSixty-five participants enrolled in E2 75 (n = 22), 100 (n = 21), and 200 (n = 22) mcg/day groups; 35 participated in the substudy. Median serum E2 concentrations in 75 and 100 mcg/day groups were <40 pg/mL. In the 200 mcg/day group, median E2 concentrations peaked on days 4-5 of CVR use at 194 pg/mL (range 114-312 pg/mL) and remained >40 pg/mL throughout 30 days; E2 concentrations were 37 pg/mL (range 28-62 pg/mL) on days 88-90 (n = 11). Among the E2 200 mcg/day substudy participants, all had withdrawal bleeding following ring removal. The 2-day ring-free interval group reported zero median unscheduled bleeding and two (range 0-16) and three (range 0-19) unscheduled spotting days in extension cycles 1 and 2, respectively. The 4-day ring-free interval group reported zero median unscheduled bleeding or spotting days.ConclusionsEstradiol concentrations with rings releasing E2 200 mcg/day and SA 200 mcg/day avoid hypoestrogenism over 30-day use.ImplicationsA 90-day contraceptive vaginal ring releasing estradiol 200 mcg/day and segesterone acetate 200 mcg/day achieves estradiol concentrations that should avoid hypoestrogenism and effectively suppresses ovulation
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