Optomotor Swimming in Larval Zebrafish Is Driven by Global Whole-Field Visual Motion and Local Light-Dark Transitions

Stabilizing gaze and position within an environment constitutes an important task for the nervous system of many animals. The optomotor response (OMR) is a reflexive behavior, present across many species, in which animals move in the direction of perceived whole-field visual motion, therefore stabilizing themselves with respect to the visual environment. Although the OMR has been extensively used to probe visuomotor neuronal circuitry, the exact visual cues that elicit the behavior remain unidentified. In this study, we use larval zebrafish to identify spatio-temporal visual features that robustly elicit forward OMR swimming. These cues consist of a local, forward-moving, off edge together with on/off symmetric, similarly directed, global motion. Imaging experiments reveal neural units specifically activated by the forward-moving light-dark transition. We conclude that the OMR is driven not just by whole-field motion but by the interplay between global and local visual stimuli, where the latter exhibits a strong light-dark asymmetry

Monopoles for Gravitation and for Higher Spin Fields

We consider massless higher spin gauge theories with both electric and magnetic sources, with a special emphasis on the spin two case. We write the equations of motion at the linear level (with conserved external sources) and introduce Dirac strings so as to derive the equations from a variational principle. We then derive a quantization condition that generalizes the familiar Dirac quantization condition, and which involves the conserved charges associated with the asymptotic symmetries for higher spins. Next we discuss briefly how the result extends to the non linear theory. This is done in the context of gravitation, where the Taub-NUT solution provides the exact solution of the field equations with both types of sources. We rederive, in analogy with electromagnetism, the quantization condition from the quantization of the angular momentum. We also observe that the Taub-NUT metric is asymptotically flat at spatial infinity in the sense of Regge and Teitelboim (including their parity conditions). It follows, in particular, that one can consistently consider in the variational principle configurations with different electric and magnetic masses.Comment: 24 page

Membrane solitons in eight-dimensional hyper-Kaehler backgrounds

We derive the BPS equations satisfied by lump solitons in $(2+1)$-dimensional sigma models with toric 8-dimensional hyper-K\"ahler (${HK}_8$) target spaces and check they preserve 1/2 of the supersymmetry. We show how these solitons are realised in M theory as M2-branes wrapping holomorphic 2-cycles in the \bE^{1,2}\times {HK}_8 background. Using the $\kappa$-symmetry of a probe M2-brane in this background we determine the supersymmetry they preserve, and note that there is a discrepancy in the fraction of supersymmetry preserved by these solitons as viewed from the low energy effective sigma model description of the M2-brane dynamics or the full M theory. Toric ${HK}_8$ manifolds are dual to a Hanany-Witten setup of D3-branes suspended between 5-branes. In this picture the lumps correspond to vortices of the three dimensional ${\mathcal N}=3$ or ${\mathcal N}=4$ theory.Comment: 12+1 pages. LaTex. v2: Typos corrected and references adde

On accentedness, intelligibility and comprehension: a pronunciation project

Treballs Finals de Grau de Mestre d'Educació Primària, Facultat d'Educació, Universitat de Barcelona, Curs: 2019-2020, Tutora: Ann Elizabeth Wilson Daily[eng] Accentedness is a normal feature in any second language student. It is along with speech intelligibility and comprehension, one of the key features of L2 communication and speech production (Tracey & Murray, 2001). In spite of this, there’s a lack of pronunciation practice in the Catalan Curriculum. Students do not work on their pronunciation skills directly and other equally important aspects are prioritized. The main objective of this final degree thesis is to create a pronunciation assessment and improvement project. It is designed to be conducted in grade six classrooms of different Catalan schools. This project takes into consideration the phonological features of speech of Spanish and/or Catalan native speakers and both the assessment test and the planned activities are designed to assess and improve both these general aspects of pronunciation and the linguistic nuances of these particular speakers.[cat] Els accents són un aspecte normal present en la majoria d’estudiants de qualsevol segona llengua. És, juntament amb la intel·ligibilitat i la comprensió del discurs produït, un dels aspectes clau a l’hora de comunicar-se utilitzant aquesta segona llengua (Tracey & Murray, 2001). Tot i això, a les escoles catalanes hi ha una mancança a nivell de currículum en aquest aspecte. La pronunciació no es treballa directament i es prioritzen altres aspectes. L’objectiu principal d’aquest treball de final és la creació d’un projecte d’avaluació i millora dels aspectes comunicatius relacionats amb la pronunciació d’alumnes de sisè de primària d’escoles catalanes. El projecte té en consideració els aspectes fonològics d’aquests alumnes amb el castellà i/o el català com a llengua materna o L1, i tant els barems d’avaluació com les activitats estan dissenyades per avaluar i millorar tant els aspectes generals de la pronunciació com aquestes idiosincràsies lingüístiques

Adaptive Locomotor Behavior in Larval Zebrafish

In this study we report that larval zebrafish display adaptive locomotor output that can be driven by unexpected visual feedback. We develop a new assay that addresses visuomotor integration in restrained larval zebrafish. The assay involves a closed-loop environment in which the visual feedback a larva receives depends on its own motor output in a way that resembles freely swimming conditions. The experimenter can control the gain of this closed feedback loop, so that following a given motor output the larva experiences more or less visual feedback depending on whether the gain is high or low. We show that increases and decreases in this gain setting result in adaptive changes in behavior that lead to a generalized decrease or increase of motor output, respectively. Our behavioral analysis shows that both the duration and tail beat frequency of individual swim bouts can be modified, as well as the frequency with which bouts are elicited. These changes can be implemented rapidly, following an exposure to a new gain of just 175 ms. In addition, modifications in some behavioral parameters accumulate over tens of seconds and effects last for at least 30 s from trial to trial. These results suggest that larvae establish an internal representation of the visual feedback expected from a given motor output and that the behavioral modifications are driven by an error signal that arises from the discrepancy between this expectation and the actual visual feedback. The assay we develop presents a unique possibility for studying visuomotor integration using imaging techniques available in the larval zebrafish

Hemangiosarcoma in the Vastus Lateralis Musculature of a Bitch - Sonographic Findings

Background: A 10-year-old spayed bitch with hip dysplasia was referred for periarticular ultrasound evaluation. A poorly marginated structure of mixed echogenicity, predominantly hypoechoic, with heterogeneous echotexture, was identified in the vastus lateralis muscle of the right pelvic limb with increased stiffness, assessed using acoustic radiation force impulse (ARFI) elastography, compared to that of the adjacent muscle tissues, and intense vascularization by pulsed Doppler and contrast-enhanced ultrasound (CEUS). Guided biopsy was performed to confirm the diagnosis of hemangiosarcoma. The objective of this study was to describe B-mode ultrasound, CEUS, and ARFI findings of hemangiosarcoma in the vastus lateralis musculature of a dog. Case: A 10-year-old spayed bitch Golden Retriever weighing 36 kg was evaluated for pelvic limb lameness. The patient presented with bilateral pain during hip extension. The primary diagnostic suspicion was degenerative joint disease and secondary hip dysplasia. The patient was referred for imaging evaluation of the hip joints (radiography and ultrasound) under anesthesia. Right lateral and ventrodorsal projections with the pelvic limbs extended were obtained to confirm the diagnosis. In the right pelvic limb, an amorphous hypoechoic structure with irregular contours and heterogeneous echotexture was observed in the vastus lateralis muscle. In ARFI elastography, it was possible to identify differences in tissue stiffness between healthy and compromised portions. Pulsed-wave Doppler evaluation demonstrated an arterial waveform pattern with a peak systolic velocity of 38.8 cm/s, end-diastolic velocity of 6.9 cm/s, pulsatility index of 1.76, and resistive index of 0.82. CEUS study identified a mean peak of 27.26 %, mean time to peak of 39.95 s, and mean transmission time of 49.96 s. The popliteal lymph node was hyperechoic and heterogeneous in B-mode. In ARFI elastography, the average stiffness was 2.52 m/s, and the CEUS obtained an average peak of 19.98%, average time to peak of 17.52 s, and mean transit time of 22.83 s. Doppler assessment revealed no clear vascularization in the lymph node. Thoracic radiography in 3 projections and abdominal ultrasonography were performed. Radiographic evidence of pulmonary nodules was not observed. On abdominal ultrasound evaluation, it was possible to identify changes in the spleen, which presented with splenomegaly, mixed echogenicity, and heterogeneous echotexture. The animal underwent ultrasound-guided muscle biopsy, which confirmed the presence of hemangiosarcoma in the muscle. The dog was referred for splenectomy and lymphadenectomy of the right popliteal, which confirmed neoplastic involvement of the same neoplasm. Discussion: On B-mode ultrasound, the observed changes were similar to those in a report of hemangiosarcoma in the muscles of the chest wall in dogs, which contributed to the diagnosis. Although it was only one patient, ARFI elastography results suggest that muscle hemangiosarcoma tends to follow the same elastographic characteristics as malignant lesions in other tissues. Additionally, the popliteal lymph node had a stiffness suggestive of malignancy (mean 2.52 m/s) because it presented a similar result and greater elasticity of metastatic axillary lymph nodes in female dogs (>2.5 m/s) and women (> 1.44 m/s) with breast tumor. With CEUS, it was possible to identify vascularization in the sentinel lymph node that was not visible by pulsed Doppler, and in muscle mass. The findings of this report provided relevant results on muscle hemangiosarcoma in a dog and demonstrated that the information obtained with the association of imaging methods supported the malignancy criteria described in other studies. Keywords: canine, imaging, diagnosis, neoplasm

Intersoliton forces in the Wess-Zumino model

The spectrum of supersymmetric domain wall solitons of the Wess-Zumino model is known to be discontinuous across a curve (of marginal stability) in the moduli space of quartic superpotentials. Here we show how this phenomenon can be understood from the behavior of the long-range inter-soliton force, which we compute by a method due to Manton.Comment: 10 pages, 4 figures, latex. Version 3, to appear in PLB, corrects minor error

Some results on optimally exercising American put options for time-inhomogeneous processes

We solve the finite-horizon, discounted, Mayer optimal stopping problem, with the gain function coming for exercising an American put option, and the underlying process modeled by adiffusion with constant volatility and a time-dependent drift satisfying certain regularity conditions. Both the corresponding value function and optimal stopping boundary are proved to be Lipschitz continuous away from the terminal time. The optimal stopping boundary is characterizedas the unique solution, up to mild regularity conditions, of the free-boundary equation. When the underlying process has Gaussian marginal distributions, more tractable expressions for the pricing formula and free-boundary equation are provided. Finally, we check that an Ornstein&-Uhlenbeck process with time-dependent parameters fulfills the required conditions assumed throughout the paper

Quantum SUSY Algebra of QQ-lumps in the Massive Grassmannian Sigma Model

We compute the $\mathcal{N}=2$ SUSY algebra of the massive Grassmannian sigma model in 2+1 dimensions. We first rederive the action of the model by using the Scherk-Schwarz dimensional reduction from $\mathcal{N}=1$ theory in 3+1 dimensions. Then, we perform the canonical quantization by using the Dirac method. We find that a particular choice of the operator ordering yields the quantum SUSY algebra of the $Q$-lumps with cental extension.Comment: 7 pages, references adde