5,830 research outputs found
Photonic band mixing in linear chains of optically coupled micro-spheres
The paper deals with optical excitations arising in a one-dimensional chain
of identical spheres due optical coupling of whispering gallery modes (WGM).
The band structure of these excitations depends significantly on the
inter-mixing between WGMs characterized by different values of angular quantum
number, . We develop a general theory of the photonic band structure of
these excitations taking these effects into account and applied it to several
cases of recent experimental interest. In the case of bands originating from
WQMs with the angular quantum number of the same parity, the calculated
dispersion laws are in good qualitative agreement with recent experiment
results. Bands resulting from hybridization of excitations resulting from
whispering gallery modes with different parity of exhibits anomalous
dispersion properties characterized by a gap in the allowed values of
\emph{wave numbers} and divergence of group velocity.Comment: RevTex, 28 pages, 7 Figure
Capacity of a bosonic memory channel with Gauss-Markov noise
We address the classical capacity of a quantum bosonic memory channel with
additive noise, subject to an input energy constraint. The memory is modeled by
correlated noise emerging from a Gauss-Markov process. Under reasonable
assumptions, we show that the optimal modulation results from a "quantum
water-filling" solution above a certain input energy threshold, similar to the
optimal modulation for parallel classical Gaussian channels. We also derive
analytically the optimal multimode input state above this threshold, which
enables us to compute the capacity of this memory channel in the limit of an
infinite number of modes. The method can also be applied to a more general
noise environment which is constructed by a stationary Gauss process. The
extension of our results to the case of broadband bosonic channels with colored
Gaussian noise should also be straightforward.Comment: 11 pages, 4 figures, final corrections mad
Probing highly obscured, self-absorbed galaxy nuclei with vibrationally excited HCN
We present high resolution (0."4) IRAM PdBI and ALMA mm and submm
observations of the (ultra) luminous infrared galaxies ((U)LIRGs)
IRAS17208-0014, Arp220, IC860 and Zw049.057 that reveal intense line emission
from vibrationally excited (=1) J=3-2 and 4-3 HCN. The emission is
emerging from buried, compact (r<17-70 pc) nuclei that have very high implied
mid-infrared surface brightness L kpc.
These nuclei are likely powered by accreting supermassive black holes (SMBHs)
and/or hot (>200 K) extreme starbursts. Vibrational, =1, lines of HCN
are excited by intense 14 micron mid-infrared emission and are excellent probes
of the dynamics, masses, and physical conditions of (U)LIRG nuclei when H
column densities exceed cm. It is clear that these lines open
up a new interesting avenue to gain access to the most obscured AGNs and
starbursts. Vibrationally excited HCN acts as a proxy for the absorbed
mid-infrared emission from the embedded nuclei, which allows for reconstruction
of the intrinsic, hotter dust SED. In contrast, we show strong evidence that
the ground vibrational state (=0), J=3-2 and 4-3 rotational lines of HCN
and HCO fail to probe the highly enshrouded, compact nuclear regions owing
to strong self- and continuum absorption. The HCN and HCO line profiles are
double-peaked because of the absorption and show evidence of non-circular
motions - possibly in the form of in- or outflows. Detections of vibrationally
excited HCN in external galaxies are so far limited to ULIRGs and early-type
spiral LIRGs, and we discuss possible causes for this. We tentatively suggest
that the peak of vibrationally excited HCN emission is connected to a rapid
stage of nuclear growth, before the phase of strong feedback.Comment: 13 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
Domestication as innovation : the entanglement of techniques, technology and chance in the domestication of cereal crops
The origins of agriculture involved pathways of domestication in which human behaviours and plant genetic adaptations were entangled. These changes resulted in consequences that were unintended at the start of the process. This paper highlights some of the key innovations in human behaviours, such as soil preparation, harvesting and threshing, and how these were coupled with genetic ‘innovations’ within plant populations. We identify a number of ‘traps’ for early cultivators, including the needs for extra labour expenditure on crop-processing and soil fertility maintenance, but also linked gains in terms of potential crop yields. Compilations of quantitative data across a few different crops for the traits of nonshattering and seed size are discussed in terms of the apparently slow process of domestication, and parallels and differences between different regional pathways are identified. We highlight the need to bridge the gap between a Neolithic archaeobotanical focus on domestication and a focus of later periods on crop-processing activities and labour organization. In addition, archaeobotanical data provide a basis for rethinking previous assumptions about how plant genetic data should be related to the origins of agriculture and we contrast two alternative hypotheses: gradual evolution with low selection pressure versus metastable equilibrium that prolonged the persistence of ‘semi-domesticated’ populations. Our revised understanding of the innovations involved in plant domestication highlight the need for new approaches to collecting, modelling and integrating genetic data and archaeobotanical evidence
Sherds as archaeobotanical assemblages: Gua Sireh reconsidered
The earliest claim for domesticated rice in Island Southeast Asia (4960–3565 cal BP) derives from a single grain embedded in a ceramic sherd from Gua Sireh Cave, Borneo. In a first assessment of spikelet-base assemblages within pottery sherds using quantitative microCT analysis, the authors found no additional rice remains within this sherd to support the early date of rice farming; analysis of a more recent Gua Sireh sherd (1990–830 cal BP), however, indicates that 70 per cent of spikelet bases are from domesticated rice. This technique offers a high degree of contextual and temporal resolution for approaching organic-tempered ceramics as well-preserved archaeobotanical assemblages
Law, Liberty and the Rule of Law (in a Constitutional Democracy)
In the hunt for a better--and more substantial--awareness of the “law,” The author intends to analyze the different notions related to the “rule of law” and to criticize the conceptions that equate it either to the sum of “law” and “rule” or to the formal assertion that “law rules,” regardless of its relationship to certain principles, including both “negative” and “positive” liberties. Instead, he pretends to scrutinize the principles of the “rule of law,” in general, and in a “constitutional democracy,” in particular, to conclude that the tendency to reduce the “democratic principle” to the “majority rule” (or “majority principle”), i.e. to whatever pleases the majority, as part of the “positive liberty,” is contrary both to the “negative liberty” and to the “rule of law” itself
The discomforting rise of ' public geographies': a 'public' conversation.
In this innovative and provocative intervention, the authors explore the burgeoning ‘public turn’ visible across the social sciences to espouse the need to radically challenge and reshape dominant and orthodox visions of ‘the academy’, academic life, and the role and purpose of the academic
Knowledge politics and new converging technologies: a social epistemological perspective
The “new converging technologies” refers to the prospect of advancing the human condition by the integrated study and application of nanotechnology, biotechnology, information technology and the cognitive sciences - or “NBIC”. In recent years, it has loomed large, albeit with somewhat different emphases, in national science policy agendas throughout the world. This article considers the political and intellectual sources - both historical and contemporary - of the converging technologies agenda. Underlying it is a fluid conception of humanity that is captured by the ethically challenging notion of “enhancing evolution”
- …