197,133 research outputs found
Many-body dark solitons in one-dimensional hard-core Bose gases
No full textThe existence and stability of solitonic states in one-dimensional repulsive Bose-Einstein condensates is investigated within a fully many-body framework by considering the limit of infinite repulsion (Tonks-Girardeau gas). A class of stationary, shape-invariant states propagating at constant velocity are explicitly found and compared to the known solution of the Gross-Pitaevskii equation. The typical features attributed to nonlinearity are thus recovered in a purely linear theory, provided the full many-particle physics is correctly accounted for. However, the formation dynamics predicted by the Gross-Pitaevskii approximation considerably differs from the exact many-body evolution
Reducing Energy Consumption in Prospective Memory Support System through Hierarchical Positioning Algorithm
No full textThe 4W project system allows providing users with location and time contextualized cues that are generated automatically starting from user expressed needs. The system comprises a server side engine capable of reasoning to find out which location categories have to be searched for and a mobile device to track user location and provide intelligent cues to the user. One of the main weaknesses of the system is the high energy toll that continuously identifying the user location with high precision has on the mobile device battery. In this paper, we describe a novel ad-hoc algorithm that leverages a hierarchical approach to adaptively decide which is the current sweet-spot sufficient for providing the needed precision in location as well as the lowest energy impact. Our experiments show a significant reduction in the energy consumption
Cell death during complete metamorphosis
No full textIn insects that undergo complete metamorphosis, cell death is essential for reshaping or removing larval tissues and organs, thus contributing to formation of the adult’s body structure. In the last few decades, the study of metamorphosis in Lepidoptera and Diptera has provided broad information on the tissue remodelling processes that occur during larva–pupa–adult transition and made it possible to unravel the underlying regulatory pathways. This review summarizes recent knowledge on cell death mechanisms in Lepidoptera and other holometabolous insects, highlighting similarities and differences with Drosophila melanogaster, and discusses the role of apoptosis and autophagy in this developmental setting.
This article is part of the theme issue ‘The evolution of complete metamorphosis’
Formation Dynamics of Black- and White-Hole Horizons in an Analogue Gravity Model
No full textWe investigate the formation dynamics of sonic horizons in a Bose gas confined in a (quasi) one-dimensional trap. This system is one of the most promising realizations of the analogue gravity paradigm and has already been successfully studied experimentally. Taking advantage of the exact solution of the one-dimensional, hard-core, Bose model (Tonks-Girardeau gas), we show that by switching on a step potential, either a sonic, black-hole-like horizon or a black/white hole pair may form, according to the initial velocity of the fluid. Our simulations never suggest the formation of an isolated white-hole horizon, although a stable stationary solution of the dynamical equations with those properties is analytically found. Moreover, we show that the semiclassical dynamics, based on the Gross-Pitaevskii equation, conforms to the exact solution only in the case of fully subsonic flows while a stationary solution exhibiting a supersonic transition is never reached dynamically
The amazing complexity of insect midgut cells: types, peculiarities, and functions
No full textThe insect midgut epithelium represents an interface between the internal and the external environment and it is the almost unique epithelial tissue by which these arthropods acquire nutrients. This epithelium is indeed able to produce digestive enzymes and to support vectorial transport of small organic nutrients, ions, and water. Moreover, it plays a key role in the defense against pathogenic microorganisms and in shaping gut microbiota. Another important midgut function is the ability to produce signaling molecules that regulate its own physiology and the activity of other organs. The two main mature cell types present in the midgut of all insects, i.e., columnar and endocrine cells, are responsible for these functions. In addition, stem cells, located at the base of the midgut epithelium, ensure the growth and renewal of the midgut during development and after injury. In insects belonging to specific orders, midgut physiology is deeply conditioned by the presence of unique cell types, i.e., goblet and copper cells, which confer peculiar features to this organ. This review reports current knowledge on the cells that form the insect midgut epithelium, focusing attention on their morphological and functional features. Notwithstanding the apparent structural simplicity of this organ, the properties of the cells make the midgut a key player in insect development and homeostasis
Change of ganglioside accessibility at the plasma membrane surface of cultured neurons, following Protein Kinase C activation
No full textWhile the mechanism of signal transduction across the plasma membrane from the exo- to the endoplasmic side has been extensively investigated, the possible return of messages back to the outer layer is less known. We studied the effect of protein kinase C activation on the ganglioside accessibility at the exoplasmic face of intact rat cerebellar granule cells in culture, using the enzyme sialidase as the probing molecule. Under the experimental conditions (1 milliunit/mL enzyme, 2 min incubation at 37 degrees C), only GT1b and GD1a gangliosides were partially affected by the enzyme (28.6 and 25.7% hydrolysis, respectively). After cell treatment with phorbol 12-myristate 13-acetate, inducing protein kinase C activation, GT1b and GD1a ganglioside susceptibility to sialidase was strongly decreased (8.6 and 15.9% hydrolysis, respectively). A reduction of ganglioside hydrolysis was also observed when protein kinase C activation was induced by cell treatment for 15 min with 100 mu M glutamate. On the contrary, accessibility did not vary when protein kinase C translocation was not effective (either in the absence of Ca2+ in the medium or using 1 mu M glutamate) or when the kinase activity was inhibited by staurosporine. These data suggest that following PKC activation, a key step of inbound transmembrane signaling, cell may dispatch outbound messages to the plasma membrane outer layer, changing the selective recognition and crypticity of glycolipids at the cell surface, possibly through a modulation of their segregation state
Sialidase in Cerebellar Granule Cells Differentiating in Culture
No full textAbstract: The optimal conditions for the assay of sialidase in cerebellar granule cells cultivated in vitro, established using f3H]GDla and 2′‐(4‐methylumbelliferyl)‐α‐D‐N‐acetyl‐neuraminic acid (MUB‐NeuNAc) as substrates, were the following: pH optimum for both substrates, 3.9; optimal molarity of sodium acetate/acetic acid buffer, 0.05 M with [3HJGDla and 0.1 M for MUB‐NeuNAc; substrate concentration for apparent maximal activity, 0.5 mM for MUB‐NeuNAc and 0.1 mM for [3H]GDla; enzyme activity linear with time up to 30 min with MUB‐NeuNAc and up to 90 min with f3HJGDla; and enzyme activity linear with enzyme protein content up to 80 μg with MUB‐NeuNAc and up to 20 μg with f3H]GDla. The assay with [3H]GDla required the presence of Triton X‐100 in a molar ratio to GDla of 15:1. Poly‐L‐lysine, which was used for plating the cells, was capable of decreasing sialidase activity against [3H]GDla/ Triton X‐100 when added to the incubation mixture. However, it had no effect on the enzyme working on MUB‐NeuNAc. Using no more than 20 μg of cellular protein, the contamination, if any, by poly‐L‐lysine released from the dish was below the concentration limit exhibiting inhibition. Using the above optimal conditions, sialidase activity was measured during cerebellar granule cell differentiation in culture. From day 0 to day 7–8 in culture, the enzyme activity rose from 20 to 130 nmol of product released/h/mg of protein with MUB‐NeuNAc and from 1 to 100 nmol of product released/ h/mg of protein with [3H]GDla. The values of enzyme activity in differentiated granule cells are the highest ever reported for mammalian sialidases in isolated cells or tissue homogenates. In fully differentiated cells, the sialidase activity against endogenous substrates was 4.2 nmol of liberated N‐acetylneuraminic acid/h/mg of protein. The marked increase of sialidase activity in cerebellar granule cells during the process of differentiation with formation of functional synapses suggests that sialidase enrichment is a marker for the same process
- …
