Sensitivity of Nonrenormalizable Trajectories to the Bare Scale

Working in scalar field theory, we consider RG trajectories which correspond to nonrenormalizable theories, in the Wilsonian sense. An interesting question to ask of such trajectories is, given some fixed starting point in parameter space, how the effective action at the effective scale, Lambda, changes as the bare scale (and hence the duration of the flow down to Lambda) is changed. When the effective action satisfies Polchinski's version of the Exact Renormalization Group equation, we prove, directly from the path integral, that the dependence of the effective action on the bare scale, keeping the interaction part of the bare action fixed, is given by an equation of the same form as the Polchinski equation but with a kernel of the opposite sign. We then investigate whether similar equations exist for various generalizations of the Polchinski equation. Using nonperturbative, diagrammatic arguments we find that an action can always be constructed which satisfies the Polchinski-like equation under variation of the bare scale. For the family of flow equations in which the field is renormalized, but the blocking functional is the simplest allowed, this action is essentially identified with the effective action at Lambda = 0. This does not seem to hold for more elaborate generalizations.Comment: v1: 23 pages, 5 figures, v2: intro extended, refs added, published in jphy

Excitation of the molecular gas in the nuclear region of M82

We present high-resolution HIFI spectroscopy of the nucleus of the archetypical starburst galaxy M 82. Six ^(12)CO lines, 2 ^(13)CO lines and 4 fine-structure lines have been detected. Besides showing the effects of the overall velocity structure of the nuclear region, the line profiles also indicate the presence of multiple components with different optical depths, temperatures, and densities in the observing beam. The data have been interpreted using a grid of PDR models. It is found that the majority of the molecular gas is in low density (n = 10^(3.5) cm^(-3)) clouds, with column densities of N_H = 10^(21.5) cm^(-2) and a relatively low UV radiation field (G_0 = 10^2). The remaining gas is predominantly found in clouds with higher densities (n = 10^5 cm^(-3)) and radiation fields (G_0 = 10^(2.75)), but somewhat lower column densities (N_H = 10^(21.2) cm^(-2)). The highest J CO lines are dominated by a small (1% relative surface filling) component, with an even higher density (n = 10^6 cm^(-3)) and UV field (G_0 = 10^(3.25)). These results show the strength of multi-component modelling for interpretating the integrated properties of galaxies

Caloric vestibular stimulation in aphasic syndrome

Caloric vestibular stimulation (CVS) is commonly used to diagnose brainstem disorder but its therapeutic application is much less established. Based on the finding that CVS increases blood flow to brain structures associated with language and communication, we assessed whether the procedure has potential to relieve symptoms of post-stroke aphasia. Three participants, each presenting with chronic, unilateral lesions to the left hemisphere, were administered daily CVS for 4 consecutive weeks. Relative to their pre-treatment baseline scores, two of the three participants showed significant improvement on both picture and responsive naming at immediate and one-week follow-up. One of these participants also showed improved sentence repetition, and another showed improved auditory word discrimination. No adverse reactions were reported. These data provide the first, albeit tentative, evidence that CVS may relieve expressive and receptive symptoms of aphasia. A larger, sham-controlled study is now needed to further assess efficacy

Low-energy properties of two-dimensional quantum triangular antiferromagnets: Non-perturbative renormalization group approach

We explore low temperature properties of quantum triangular Heisenberg antiferromagnets in two dimension in the vicinity of the quantum phase transition at zero temperature. Using the effective field theory described by the $SO(3)\times SO(2)/SO(2)$ matrix Ginzburg-Landau-Wilson model and the non-perturbative renormalization group method, we clarify how quantum and thermal fluctuations affect long-wavelength behaviors in the parameter region where the systems exhibit a fluctuation-driven first order transition to a long-range ordered state. We show that at finite temperatures the crossover from a quantum $\phi^6$ theory to a renormalized two-dimensional classical nonlinear sigma model region appears, and in this crossover region, massless fluctuation modes with linear dispersion a la spin waves govern low-energy physics. Our results are in good agreement with the recent experimental observations for the two-dimensional triangular Heisenberg spin system, NiGa$_2$S$_4$.Comment: 14 pages,7 figures, version accepted for publication in Physical Review

Interstellar CH absorption in the diffuse interstellar medium along the sight-lines to G10.6–0.4 (W31C), W49N, and W51

We report the detection of the ground state N, J = 1, 3/2 → 1, 1/2 doublet of the methylidyne radical CH at ~532 GHz and ~536 GHz with the Herschel/HIFI instrument along the sight-line to the massive star-forming regions G10.6–0.4 (W31C), W49N, and W51. While the molecular cores associated with these massive star-forming regions show emission lines, clouds in the diffuse interstellar medium are detected in absorption against the strong submillimeter background. The combination of hyperfine structure with emission and absorption results in complex profiles, with overlap of the different hyperfine components. The opacities of most of the CH absorption features are linearly correlated with those of CCH, CN, and HCO^+ in the same velocity intervals. In specific narrow velocity intervals, the opacities of CN and HCO^+ deviate from the mean trends, giving rise to more opaque absorption features. We propose that CCH can be used as another tracer of the molecular gas in the absence of better tracers, with [CCH]/[H_2] ~3.2 ± 1.1 × 10^(−8). The observed [CN]/[CH], [CCH]/[CH] abundance ratios suggest that the bulk of the diffuse matter along the lines of sight has gas densities n_H = n(H) + 2n(H_2) ranging between 100 and 1000 cm^(−3)

Excitation and abundance of C_3 in star forming cores: Herschel/HIFI observations of the sight-lines to W31C and W49N

We present spectrally resolved observations of triatomic carbon (C_3) in several ro-vibrational transitions between the vibrational ground state and the low-energy ν_2 bending mode at frequencies between 1654−1897 GHz along the sight-lines to the submillimeter continuum sources W31C and W49N, using Herschel’s HIFI instrument. We detect C_3 in absorption arising from the warm envelope surrounding the hot core, as indicated by the velocity peak position and shape of the line profile. The sensitivity does not allow to detect C_3 absorption due to diffuse foreground clouds. From the column densities of the rotational levels in the vibrational ground state probed by the absorption we derive a rotation temperature (T_(rot)) of ~50−70 K, which is a good measure of the kinetic temperature of the absorbing gas, as radiative transitions within the vibrational ground state are forbidden. It is also in good agreement with the dust temperatures for W31C and W49N. Applying the partition function correction based on the derived T_(rot), we get column densities N(C_3) ~ 7−9 × 10^(14) cm^(−2) and abundance x(C_3) ~ 10^(−8) with respect to H_2. For W31C, using a radiative transfer model including far-infrared pumping by the dust continuum and a temperature gradient within the source along the line of sight we find that a model with x(C_3) = 10^(−8), T_(kin) = 30−50 K, N(C_3) = 1.5 × 10^(15) cm^(−2) fits the observations reasonably well and provides parameters in very good agreement with the simple excitation analysis

Nitrogen hydrides in interstellar gas: Herschel/HIFI observations towards G10.6-0.4 (W31C)

The HIFI instrument on board the Herschel Space Observatory has been used to observe interstellar nitrogen hydrides along the sight-line towards G10.6−0.4 in order to improve our understanding of the interstellar chemistry of nitrogen. We report observations of absorption in NH N = 1 ← 0, J = 2 ← 1 and ortho-NH_2 1_(1,1) ← 0_(0,0). We also observed ortho-NH_3 1_0 ← 0_0, and 2_0 ← 1_0, para-NH_3 2_1 ← 1_1, and searched unsuccessfully for NH^+. All detections show emission and absorption associated directly with the hot-core source itself as well as absorption by foreground material over a wide range of velocities. All spectra show similar, non-saturated, absorption features, which we attribute to diffuse molecular gas. Total column densities over the velocity range 11−54 km s^(−1) are estimated. The similar profiles suggest fairly uniform abundances relative to hydrogen, approximately 6 × 10^(−9), 3 × 10^(−9), and 3 × 10^(−9) for NH, NH_2, and NH_3, respectively. These abundances are discussed with reference to models of gas-phase and surface chemistry

Particle Computation: Complexity, Algorithms, and Logic

We investigate algorithmic control of a large swarm of mobile particles (such as robots, sensors, or building material) that move in a 2D workspace using a global input signal (such as gravity or a magnetic field). We show that a maze of obstacles to the environment can be used to create complex systems. We provide a wide range of results for a wide range of questions. These can be subdivided into external algorithmic problems, in which particle configurations serve as input for computations that are performed elsewhere, and internal logic problems, in which the particle configurations themselves are used for carrying out computations. For external algorithms, we give both negative and positive results. If we are given a set of stationary obstacles, we prove that it is NP-hard to decide whether a given initial configuration of unit-sized particles can be transformed into a desired target configuration. Moreover, we show that finding a control sequence of minimum length is PSPACE-complete. We also work on the inverse problem, providing constructive algorithms to design workspaces that efficiently implement arbitrary permutations between different configurations. For internal logic, we investigate how arbitrary computations can be implemented. We demonstrate how to encode dual-rail logic to build a universal logic gate that concurrently evaluates and, nand, nor, and or operations. Using many of these gates and appropriate interconnects, we can evaluate any logical expression. However, we establish that simulating the full range of complex interactions present in arbitrary digital circuits encounters a fundamental difficulty: a fan-out gate cannot be generated. We resolve this missing component with the help of 2x1 particles, which can create fan-out gates that produce multiple copies of the inputs. Using these gates we provide rules for replicating arbitrary digital circuits.Comment: 27 pages, 19 figures, full version that combines three previous conference article

Electronic temperature sensing yarn

This paper reports the development of an electronic temperature sensing (ETS) yarn by embedding commercially available thermistors within the fibres of a yarn. The thermistor is initially soldered onto a fine copper wire and then encapsulated to form a polymer micro-pod. The micro-pod protects the thermistor from mechanical and chemical stresses. Thereafter the fine copper wire with micro-pods is covered by a tubular warp knitted structure to craft the final ETS yarn. The miniature size of the micro-pod makes the electronics invisible to the wearer. Such a yarn can be used to knit or weave any textile structure. It is also capable of providing temperature readings at a given point (localised) and can be used to make a wearable thermograph. Where the ETS yarn is included in a garment, it can be safely washed