139 research outputs found
Radiative capture of polarized neutrons by polarized protons
A model-independent irreducible tensor approach to p(n,gamma)d is presented
and an explicit form for the spin-structure of the matrix for the reaction is
obtained in terms of the Pauli spin-matrices for the neutron and the proton.
Expressing the multipole amplitudes in terms of the triplet --> triplet and
singlet --> triplet transitions, we point out how the initial singlet and
triplet contributions to the differential cross section can be determined
empirically.Comment: Revised version; typeset using RevTeX4; 6 pages, no figure
Phase ambiguity of the threshold amplitude in pp -> pp\pi^0
Measurements of spin observables in pp -> {\vec p}{\vec p}\pi^0 are suggested
to remove the phase ambiguity of the threshold amplitude. The suggested
measurements complement the IUCF data on {\vec p}{\vec p} -> pp\pi^0 to
completely determine all the twelve partial wave amplitudes, taken into
consideration by Mayer et.al. [15] and Deepak, Haidenbauer and Hanhart [20].Comment: 4 pages, 1 table
Classical light analogue of the nonlocal Aharonov-Bohm effect
We demonstrate the existence of a non-local geometric phase in the
intensity-intensity correlations of classical incoherent light, that is not
seen in the lower order correlations. This two-photon Pancharatnam phase was
observed and modulated in a Mach-Zehnder interferometer. Using acousto-optic
interaction, independent phase noise was introduced to light in the two arms of
the interferometer to create two independent incoherent classical sources from
laser light. The experiment is the classical optical analogue of the
multi-particle Aharonov-Bohm effect. As the trajectory of light over the
Poincare sphere introduces a phase shift observable only in the
intensity-intensity correlation, it provides a means of deflecting the
two-photon wavefront, while having no effect on single photons.Comment: To appear in Europhys. Let
Light scattering from a magnetically tunable dense random medium with weak dissipation : ferrofluid
We present a semi-phenomenological treatment of light transmission through
and its reflection from a ferrofluid, which we regard as a magnetically tunable
system of dense random dielectric scatterers with weak dissipation. Partial
spatial ordering is introduced by the application of a transverse magnetic
field that superimposes a periodic modulation on the dielectric randomess. This
introduces Bragg scattering which effectively enhances the scattering due to
disorder alone, and thus reduces the elastic mean free path towards Anderson
localization. Our theoretical treatment, based on invariant imbedding, gives a
simultaneous decrease of transmission and reflection without change of incident
linear polarisation as the spatial order is tuned magnetically to the Bragg
condition, namely the light wave vector being equal to half the Bragg vector
(Q). Our experimental observations are in qualitative agreement with these
results. We have also given expressions for the transit (sojourn) time of light
and for the light energy stored in the random medium under steady illumination.
The ferrofluid thus provides an interesting physical realization of effectively
a "Lossy Anderson-Bragg" (LAB) cavity with which to study the effect of the
interplay of spatial disorder, partial order and weak dissipation on light
transport. Given the current interest in propagation, optical limiting and
storage of light in ferrofluids, the present work seems topical
Do Language Embeddings Capture Scales?
Pretrained Language Models (LMs) have been shown to possess significant
linguistic, common sense, and factual knowledge. One form of knowledge that has
not been studied yet in this context is information about the scalar magnitudes
of objects. We show that pretrained language models capture a significant
amount of this information but are short of the capability required for general
common-sense reasoning. We identify contextual information in pre-training and
numeracy as two key factors affecting their performance and show that a simple
method of canonicalizing numbers can have a significant effect on the results.Comment: Accepted at EMNLP Findings 2020 and EMNLP BlackboxNLP workshop 2020;
8 pages, 2 figures; Minor changes to the acknowledgment sectio
LAMBADA: Backward Chaining for Automated Reasoning in Natural Language
Remarkable progress has been made on automated reasoning with knowledge
specified as unstructured, natural text, by using the power of large language
models (LMs) coupled with methods such as Chain-of-Thought prompting and
Selection-Inference. These techniques search for proofs in the forward
direction from axioms to the conclusion, which suffers from a combinatorial
explosion of the search space, and thus high failure rates for problems
requiring longer chains of reasoning. The classical automated reasoning
literature has shown that reasoning in the backward direction (i.e. from the
intended conclusion to the set of axioms that support it) is significantly more
efficient at proof-finding problems. We import this intuition into the LM
setting and develop a Backward Chaining algorithm, which we call LAMBADA, that
decomposes reasoning into four sub-modules, each of which can be simply
implemented by few-shot prompted LM inference. We show that LAMBADA achieves
massive accuracy boosts over state-of-the-art forward reasoning methods on two
challenging logical reasoning datasets, particularly when deep and accurate
proof chains are required.Comment: 16 page
An unusual presentation of carcinoma stomach
Symptomatic gastric malignancy usually presents with symptoms which mimic peptic ulcer disease.Usual presenting features include weight loss and abdominal pain. Other symptoms include nausea, vomiting, dysphagia, melena and early satiety. Gastric malignancy presenting with hemetemesis, macular skin lesions of DIC and low backache due to bone metastasis from the primary is rare. Also bone metastasis in gastric cancer in the absence of hepatic metastasis is also rare.Pan African Medical Journal 2013; 14: 8
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