9,326 research outputs found
The sinews of war: ancient catapults
Although they were probably already used in ancient Mesopotamia, catapults became increasingly common in the Mediterranean area from the 4th century B.C. Their design was improved over time through a combination of trial-and-error and geometrical procedures. By the 1st century A.D., it was possible to compile accurate tables of specifications for catapults of different size, and to build engines capable of hurling heavy projectiles at a distance of more than a hundred meters. In her essay, Cuomo asks who the men behind these machines were. What motivated the ancient military engineers, and how did they relate to their artifacts? And who did they work for? The author shows that ancient catapults provide unique insights into the interface of science and war, theory and practice, politics and knowledge
Technology and culture in Greek and Roman antiquity
The technological achievements of the Greeks and Romans continue to fascinate and excite admiration. But what was the place of technology in their cultures? Through five case-studies, this book sets ancient technical knowledge in its political, social and intellectual context. It explores the definition of the techne of medicine in classical Athens, the development of new military technology in Hellenistic times, the self-image of technicians through funerary art in the early Roman Empire, the resolution of boundary disputes in the early second century AD, and the status of architecture and architects in late antiquity. Deploying a wide range of evidence, it reconstructs a dialectic picture of ancient technology, where several ancient points of view are described and analyzed, and their interaction examined. Dr Cuomo argues for the centrality of technology to the ancient world-picture, and for its extraordinarily rich political, social, economic and religious significance.
âą Offers five in-depth, varied case-studies, each with a slightly different methodological focus âą Covers a broad period from classical Athens to late antiquity and a wide range of disciplines âą Only book of its kind to make extensive use of non-textual material and of the newest historiographical approaches from both classics and the history of science and technology
Contents
Introduction; 1. The definition of techne in classical Athens; 2. The Hellenistic military revolution; 3. Death and the craftsman; 4. Boundary disputes in the Roman Empire; 5. Architects of late antiquity; Epilogue
Migraine and motion sickness: what is the link?
The brainstem is a structurally complex region, containing numerous ascending and descending fibres that converge on centres that regulate bodily functions essential to life. Afferent input from the cranial tissues and the special senses is processed, in part, in brainstem nuclei. In addition, brainstem centres modulate the flow of pain messages and other forms of sensory information to higher regions of the brain, and influence the general excitability of these cortical regions. Thus, disruptions in brainstem processing might evoke a complex range of unpleasant symptoms, vegetative changes and neurovascular disturbances and that, together, form attacks of migraine. Migraine is linked with various co-morbid conditions, the most prominent being motion sickness. Symptoms such as nausea, dizziness and headache are common to motion sickness and migraine; moreover, migraine sufferers have a heightened vulnerability to motion sickness. As both maladies involve reflexes that relay in the brainstem, symptoms may share the same neural circuitry. In consequence, subclinical interictal persistence of disturbances in these brainstem pathways could not only increase vulnerability to recurrent attacks of migraine but also increase susceptibility to motion sickness. Mechanisms that mediate symptoms of motion sickness and migraine are explored in this paper. The physiology of motion sickness and migraine is discussed, and neurotransmitters that may be involved in the manifestation of symptoms are reviewed. Recent findings have shed light on the relationship between migraine and motion sickness, and provide insights into the generation of migraine attacks
Towards a Distributed Quantum Computing Ecosystem
The Quantum Internet, by enabling quantum communications among remote quantum
nodes, is a network capable of supporting functionalities with no direct
counterpart in the classical world. Indeed, with the network and communications
functionalities provided by the Quantum Internet, remote quantum devices can
communicate and cooperate for solving challenging computational tasks by
adopting a distributed computing approach. The aim of this paper is to provide
the reader with an overview about the main challenges and open problems arising
with the design of a Distributed Quantum Computing ecosystem. For this, we
provide a survey, following a bottom-up approach, from a communications
engineering perspective. We start by introducing the Quantum Internet as the
fundamental underlying infrastructure of the Distributed Quantum Computing
ecosystem. Then we go further, by elaborating on a high-level system
abstraction of the Distributed Quantum Computing ecosystem. Such an abstraction
is described through a set of logical layers. Thereby, we clarify dependencies
among the aforementioned layers and, at the same time, a road-map emerges
General Bootstrap Equations in 4D CFTs
We provide a framework for generic 4D conformal bootstrap computations. It is
based on the unification of two independent approaches, the covariant
(embedding) formalism and the non-covariant (conformal frame) formalism. We
construct their main ingredients (tensor structures and differential operators)
and establish a precise connection between them. We supplement the discussion
by additional details like classification of tensor structures of n-point
functions, normalization of 2-point functions and seed conformal blocks,
Casimir differential operators and treatment of conserved operators and
permutation symmetries. Finally, we implement our framework in a Mathematica
package and make it freely available.Comment: 57 page
An error estimate of Gaussian Recursive Filter in 3Dvar problem
Computational kernel of the three-dimensional variational data assimilation
(3D-Var) problem is a linear system, generally solved by means of an iterative
method. The most costly part of each iterative step is a matrix-vector product
with a very large covariance matrix having Gaussian correlation structure. This
operation may be interpreted as a Gaussian convolution, that is a very
expensive numerical kernel. Recursive Filters (RFs) are a well known way to
approximate the Gaussian convolution and are intensively applied in the
meteorology, in the oceanography and in forecast models. In this paper, we deal
with an oceanographic 3D-Var data assimilation scheme, named OceanVar, where
the linear system is solved by using the Conjugate Gradient (GC) method by
replacing, at each step, the Gaussian convolution with RFs. Here we give
theoretical issues on the discrete convolution approximation with a first order
(1st-RF) and a third order (3rd-RF) recursive filters. Numerical experiments
confirm given error bounds and show the benefits, in terms of accuracy and
performance, of the 3-rd RF.Comment: 9 page
Computation of the inverse Laplace Transform based on a Collocation method which uses only real values
We develop a numerical algorithm for inverting a Laplace transform (LT), based on Laguerre polynomial series expansion of the
inverse function under the assumption that the LT is known on the real axis only. The method belongs to the class of Collocation
methods (C-methods), and is applicable when the LT function is regular at infinity. Difficulties associated with these problems are due
to their intrinsic ill-posedness. The main contribution of this paper is to provide computable estimates of truncation, discretization,
conditioning and roundoff errors introduced by numerical computations. Moreover, we introduce the pseudoaccuracy which will be
used by the numerical algorithm in order to provide uniform scaled accuracy of the computed approximation for any x with respect
to ex . These estimates are then employed to dynamically truncate the series expansion. In other words, the number of the terms of
the series acts like the regularization parameter which provides the trade-off between errors.
With the aim to validate the reliability and usability of the algorithm experiments were carried out on several test functions
Sph propagation modelling of an earthflow from southern italy
Natural slopes in clayey soils are often affected by failures which may cause the onset of landslides of the flow type travelling large distances and damaging buildings and major infrastructures. Particularly, the so-called earthflows pose challenging tasks for the individuation and forecasting of the remobilized masses; as a consequence, the mathematical modelling of the propagation stage allows enhancing the understanding of earthflows in order to obtain reliable assessments of run-out distances and displaced soil volumes. This paper deals with the reactivations of Montaguto earthflow (Southern Italy) occurred from 1998 to 2009 that are simulated, through the depth-integrated âGeoFlow-SPHâ model, thanks to the availability of a detailed data-set. The achieved results provide a satisfactory agreement with the in-situ information and outline how a change of the rheology of the mobilized masses can affect the whole phenomenon
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