Modeling the mobility of living organisms in heterogeneous landscapes: Does memory improve foraging success?

Thanks to recent technological advances, it is now possible to track with an unprecedented precision and for long periods of time the movement patterns of many living organisms in their habitat. The increasing amount of data available on single trajectories offers the possibility of understanding how animals move and of testing basic movement models. Random walks have long represented the main description for micro-organisms and have also been useful to understand the foraging behaviour of large animals. Nevertheless, most vertebrates, in particular humans and other primates, rely on sophisticated cognitive tools such as spatial maps, episodic memory and travel cost discounting. These properties call for other modeling approaches of mobility patterns. We propose a foraging framework where a learning mobile agent uses a combination of memory-based and random steps. We investigate how advantageous it is to use memory for exploiting resources in heterogeneous and changing environments. An adequate balance of determinism and random exploration is found to maximize the foraging efficiency and to generate trajectories with an intricate spatio-temporal order. Based on this approach, we propose some tools for analysing the non-random nature of mobility patterns in general.Comment: 14 pages, 4 figures, improved discussio

Detection of quantum light in the presence of noise

Detection of quantum light in the presence of dark counts and background radiation noise is considered. The corresponding positive operator-valued measure is obtained and photocounts statistics of quantum light in the presence of noise is studied.Comment: 4 pages, 1 figure; misprints correcte

Introducing Christianity into Christendom: investigating the affinity between Søren Kierkegaard and the early thought of Karl Barth

The Swiss theologian Karl Barth’s (1886-1968) relation to the Danish thinker Søren Kierkegaard (1813-1855) is one which has been touched upon repeatedly with regard to influence and parallels. It is an issue that has produced diverse conclusions ranging from that of T. F. Torrance, who believed Barth to have been influenced by Kierkegaard to an extent even unknown to himself, to the likes of Bruce McCormack who views the affinity as exaggerated. However, this intriguing relationship refuses a conclusive position regarding the extent to which Barth had been influenced by Kierkegaard; any attempt that seeks to resolve this question disregards both the complexity of Barth’s thought and the sheer range of thinkers who had contributed to his theological development. Moreover, Barth’s own comments on the influence of Kierkegaard on his development complicate the investigation into the relationship between the two. Whereas in 1922 Barth admits a dependence on Kierkegaard in the second edition of The Epistle to the Romans, by 1963 he has assumed a more cautious relation to Kierkegaard

Use of ultrasound densitometry for the assess of structural and functional disorders of bone tissue and prediction of fractures risk

To determine the dependence of lumbar spine compression degree on BMD state and the patients’ age. The relationship of BMD state, the patients’ age and the degree of compression of the vertebrae were studied. Correlation and regression analysis of the relationship between SOS index, score of compression and patients' age have been examined. Results. The data obtained allowed us to develop a mathematical model for predicting BMD reduction and the severity of vertebral compression fractures. Conclusions. Ultrasonic indexes of bone mineral density may be used not only for its screening assessment in general population of different ages, but also in assessing the degree of structural and functional changes of BT, predicting the severity of low-energy osteoporosis fractures. It will help to assign treatment in preclinical stage, and carry out prevention of compression fractures

Deconvolution problems in x-ray absorption fine structure

A Bayesian method application to the deconvolution of EXAFS spectra is considered. It is shown that for purposes of EXAFS spectroscopy, from the infinitely large number of Bayesian solutions it is possible to determine an optimal range of solutions, any one from which is appropriate. Since this removes the requirement for the uniqueness of solution, it becomes possible to exclude the instrumental broadening and the lifetime broadening from EXAFS spectra. In addition, we propose several approaches to the determination of optimal Bayesian regularization parameter. The Bayesian deconvolution is compared with the deconvolution which uses the Fourier transform and optimal Wiener filtering. It is shown that XPS spectra could be in principle used for extraction of a one-electron absorptance. The amplitude correction factors obtained after deconvolution are considered and discussed.Comment: 6 two-column pages, 5 eps figures; submitted to J. Phys.: Appl. Phy

Spontaneous symmetry breaking in amnestically induced persistence

We investigate a recently proposed non-Markovian random walk model characterized by loss of memories of the recent past and amnestically induced persistence. We report numerical and analytical results showing the complete phase diagram, consisting of 4 phases, for this system: (i) classical nonpersistence, (ii) classical persistence (iii) log-periodic nonpersistence and (iv) log-periodic persistence driven by negative feedback. The first two phases possess continuous scale invariance symmetry, however log-periodicity breaks this symmetry. Instead, log-periodic motion satisfies discrete scale invariance symmetry, with complex rather than real fractal dimensions. We find for log-periodic persistence evidence not only of statistical but also of geometric self-similarity.Comment: 4 pages, 2 color fig

Seshat: The Global History Databank

The vast amount of knowledge about past human societies has not been systematically organized and, therefore, remains inaccessible for empirically testing theories about cultural evolution and historical dynamics. For example, what evolutionary mechanisms were involved in the transition from the small-scale, uncentralized societies, in which humans lived 10,000 years ago, to the large-scale societies with an extensive division of labor, great differentials in wealth and power, and elaborate governance structures of today? Why do modern states sometimes fail to meet the basic needs of their populations? Why do economies decline, or fail to grow? In this article, we describe the structure and uses of a massive databank of historical and archaeological information, Seshat: The Global History Databank. The data that we are currently entering in Seshat will allow us and others to test theories explaining how modern societies evolved from ancestral ones, and why modern societies vary so much in their capacity to satisfy their members’ basic human needsPeer reviewedFinal Published versio

Biomechanical characteristics of different fixing methods of fractures of the talus

Досліджено характеристики жорсткості та надійність фіксації переломів стандартними та зустрічно-компресуючими гвинтами, що фіксують переломи тіла та шийки таранної кістки у реальних, включаючи циклічні, режимах дії зовнішніх навантажень. При передачі стискаючого зусилля на відламок тип фіксуючих гвинтів суттєво впливає на деформації системи остеосинтезу при всіх рівнях навантаження; залишкові деформації (взаємний зсув відламків) систем з зустрічно-компресуючими гвинтами суттєво менше залишкових деформацій систем з стандартними гвинтами. Застосування нових типів гвинтів суттєво підвищує стабільність фіксації та в цілому збільшує механічну надійність фіксації переломів таранної кістки.Purpose. Subject matter of the present paper is to investigate the characteristics of hardness and fixation of fractures with standard and self-tightening screws, fixing the oblique talus fracture in real regimes of external load including the cyclic ones. Design/methodology/approach. During the experiment the specimen of limbs without pathology of the bone tissue had been used. Fixation of the bone fragments (osteosynthesis) had been performed by the means of standard and self-tightening screws. Tests were conducted by transferring the load on fixed distal fragment fracture of the talus in the craneal direction. Downloads modes: one static and impact more cyclically variable loads that simulate human weight. Findings. During the transmission of the compressing force onto the fragment, the type of the fixing screw greatly influences the deformation of the osteosynthetic systems at all levels of load; permanent residual deformations (mutual shift of fragments) of the systems with self-tightening screws are much more lower if compared to the ones of the systems, employing the standard ones. Employment of the new type of screws significantly increases the fixation stability and generally increases the mechanical durability of the fixation of the oblique fracture of the talus fracture. Originality/value. Results are important for medicine and can improve treatment.В статье исследованы характеристики жесткости и надежность фиксации переломов стандартными и самокомпрессирующимися винтами, которые фиксируют перелом тела и шейки таранной кости в реальных, включая циклические, режимах действия внешних загрузок. При передачи сжимающего усилия на отломок тип фиксирующих винтов существенно влияет на деформации системы остеосинтеза при всех уровнях нагрузок; остаточные деформации (взаимный сдвиг отломков) систем с самокомпрессирующими винтами существенно меньше остаточных деформаций систем со стандартными винтами. Использование новых типов винтов существенно повышает стабильность фиксации и в целом увеличивает механическую надежность фиксации переломов таранной кости

A next-generation inverse-geometry spallation-driven ultracold neutron source

The physics model of a next-generation spallation-driven high-current ultracold neutron (UCN) source capable of delivering an extracted UCN rate of around an-order-of-magnitude higher than the strongest proposed sources, and around three-orders-of-magnitude higher than existing sources, is presented. This UCN-current-optimized source would dramatically improve cutting-edge UCN measurements that are currently statistically limited. A novel "Inverse Geometry" design is used with 40 L of superfluid $^4$He (He-II), which acts as a converter of cold neutrons (CNs) to UCNs, cooled with state-of-the-art sub-cooled cryogenic technology to $\sim$1.6 K. Our design is optimized for a 100 W maximum heat load constraint on the He-II and its vessel. In our geometry, the spallation target is wrapped symmetrically around the UCN converter to permit raster scanning the proton beam over a relatively large volume of tungsten spallation target to reduce the demand on the cooling requirements, which makes it reasonable to assume that water edge-cooling only is sufficient. Our design is refined in several steps to reach $P_{UCN}=2.1\times10^9\,/$s under our other restriction of 1 MW maximum available proton beam power. We then study effects of the He-II scattering kernel as well as reductions in $P_{UCN}$ due to pressurization to reach $P_{UCN}=1.8\times10^9\,/$s. Finally, we provide a design for the UCN extraction system that takes into account the required He-II heat transport properties and implementation of a He-II containment foil that allows UCN transmission. We estimate a total useful UCN current from our source of $R_{use}=5\times10^8\,/$s from a 18 cm diameter guide 5 m from the source. Under a conservative "no return" approximation, this rate can produce an extracted density of $>1\times10^4\,/$cm$^3$ in $<$1000~L external experimental volumes with a $^{58}$Ni (335 neV) cut-off potential.Comment: Submitted to Journal of Applied Physic

Amnestically induced persistence in random walks

We study how the Hurst exponent $\alpha$ depends on the fraction $f$ of the total time $t$ remembered by non-Markovian random walkers that recall only the distant past. We find that otherwise nonpersistent random walkers switch to persistent behavior when inflicted with significant memory loss. Such memory losses induce the probability density function of the walker's position to undergo a transition from Gaussian to non-Gaussian. We interpret these findings of persistence in terms of a breakdown of self-regulation mechanisms and discuss their possible relevance to some of the burdensome behavioral and psychological symptoms of Alzheimer's disease and other dementias.Comment: 4 pages, 3 figs, subm. to Phys. Rev. Let