1,373 research outputs found
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Additive Manufacturing with RepRap Methodology: Current Situation and Future Prospects
In February 2004, Adrian Bowyer, from the University of Bath, began an open initiative
called RepRap, with the purpose of creating an open source rapid prototyping machine
which, moreover, could replicate itself. This article analyzes the current status of the
RepRap initiative, commenting the basic components of RepRap machines, the
differences between the different 3D printers developed by the RepRap community so
far, and the technical possibilities that opens this technology from the engineering point
of view. In addition we propose some improvements that could be perfectly feasible in
the short term. For this purpose, the assembly of a RepRap Mendel Prusa was
performed, but with some modifications.Mechanical Engineerin
Towards a population of HMXB/NS microquasars as counterparts of low-latitude unidentified EGRET sources
The discovery of the microquasar LS 5039 well within the 95% conficence
contour of the Unidentified EGRET Source (UES) 3EG J1824-1514 was a major step
towards the possible association between microquasars (MQs) and UESs. The
recent discovery of precessing relativistic radio jets in LS I +61 303, a
source associated for long time with 2CG 135+01 and with the UES 3EG
J0241+6103, has given further support to this idea. Finally, the very recently
proposed association between the microquasar candidate AX J1639.0-4642 and the
UES 3EG J1639-4702 points towards a population of High Mass X-ray Binary
(HMXB)/Neutron Star (NS) microquasars as counterparts of low-latitude
unidentified EGRET sources.Comment: 12 pages, 7 figures. Proceedings of the Conference "The
Multiwavelength Approach to Unidentified Gamma-ray Sources", to appear in the
journal Astrophysics and Space Scienc
Growth of the deep water rose shrimp Parapenaeus longirostris in Mauritanian waters (NW Africa)
The deep water rose shrimp Parapenaeus longirostris is the main target species of a Spanish fleet of shrimp bottom trawlers operating in the Mauritanian EEZ. The life history of this species is well known in north eastern Atlantic and Mediterranean waters, while the information is quite limited for the eastern central Atlantic. Biological samplings of the species were conducted by scientific observers onboard this fleet, from catches obtained during 17 fishing trips performed between March 2014 and June 2019. The carapace lengths (CL) of 91662 specimens (54% females and 46% males) were grouped in 33 monthly length frequency distributions. For the study of the length–age relationship, the Von Bertalanffy Growth Function (VBGF) was fit to the monthly length distributions by using the ELEFAN I routine followed by separating the frequency histograms into normal components through the Bhattacharya’s method and the NORMSEP routine. These analyses were carried out separately for males, females, and combined sexes, using the FISAT II automatic calculation program. CL of females and males ranged from 11.6 to 39.2 mm and 10.5 to 30.5 mm, respectively. Three and five modal components (annual cohorts) were identified for females and males, respectively. The growth function estimated parameters were CL∞=41.74, k=0.51 for combined sexes, CL∞= 41.67, k= 0.51 for females and CL∞= 32.24, k=0.84 for males. Estimated growth performance indices were around 2.95 for combined sexes, females and males. The estimated parameters may be used as input to test length-based methodologies for the assessment of this data-limited stock, for which only production models have been used so far
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PPAR<i>γ</i> agonist-loaded PLGA -PEG nanocarriers as a potential treatment for Alzheimer’s disease: in vitro and in vivo studies
Objective: The first aim of this study was to develop a nanocarrier that could transport the peroxisome proliferator-activated receptor agonist, pioglitazone (PGZ) across brain endothelium and examine the mechanism of nanoparticle transcytosis. The second aim was to determine whether these nanocarriers could successfully treat a mouse model of Alzheimer’s disease (AD).
Methods: PGZ-loaded nanoparticles (PGZ-NPs) were synthesized by the solvent displacement technique, following a factorial design using poly (lactic-co-glycolic acid) polyethylene glycol (PLGA-PEG). The transport of the carriers was assessed in vitro, using a human brain endothelial cell line, cytotoxicity assays, fluorescence-tagged nanocarriers, fluorescence-activated cell sorting, confocal and transmission electron microscopy. The effectiveness of the treatment was assessed in APP/PS1 mice in a behavioral assay and by measuring the cortical deposition of β-amyloid.
Results: Incorporation of PGZ into the carriers promoted a 50x greater uptake into brain endothelium compared with the free drug and the carriers showed a delayed release profile of PGZ in vitro. In the doses used, the nanocarriers were not toxic for the endothelial cells, nor did they alter the permeability of the blood–brain barrier model. Electron microscopy indicated that the nanocarriers were transported from the apical to the basal surface of the endothelium by vesicular transcytosis. An efficacy test carried out in APP/PS1 transgenic mice showed a reduction of memory deficit in mice chronically treated with PGZ-NPs. Deposition of β-amyloid in the cerebral cortex, measured by immunohistochemistry and image analysis, was correspondingly reduced.
Conclusion: PLGA-PEG nanocarriers cross brain endothelium by transcytosis and can be loaded with a pharmaceutical agent to effectively treat a mouse model of AD
Guiding the Way to Gamma-Ray Sources: X-ray Studies of Supernova Remnants
Supernova remnants have long been suggested as a class of potential
counterparts to unidentified gamma-ray sources. The mechanisms by which such
gamma-rays can arise may include emission from a pulsar associated with a
remnant, or a variety of processes associated with energetic particles
accelerated by the SNR shock. Imaging and spectral observations in the X-ray
band can be used to identify properties of the remnants that lead to gamma-ray
emission, including the presence of pulsar-driven nebulae, nonthermal X-ray
emission from the SNR shells, and the interaction of SNRs with dense
surrounding material.Comment: 16 pages, 11 figures, To appear in the proceedings of the workshop:
"The Nature of the Unidentified Galactic Gamma-Ray Sources" held at INAOE,
Mexico, October 2000, (A.Carraminana, O. Reiner and D. Thompson, eds.
The Multiwavelength Approach to Unidentified Gamma-Ray Sources
As the highest-energy photons, gamma rays have an inherent interest to
astrophysicists and particle physicists studying high-energy, nonthermal
processes. Gamma-ray telescopes complement those at other wavelengths,
especially radio, optical, and X-ray, providing the broad, mutiwavelength
coverage that has become such a powerful aspect of modern astrophysics.
Multiwavelength techniques of various types have been developed to help
identify and explore unidentified gamma-ray sources. This overview summarizes
the ideas behind several of these methods.Comment: Proceedings of the Conference "The Multiwavelength Approach to
Unidentified Sources", to appear in the journal Astrophysics and Space
Scienc
Unidentified gamma-ray sources off the Galactic plane as low-mass microquasars?
A subset of the unidentified EGRET gamma-ray sources with no active galactic
nucleus or other conspicuous counterpart appears to be concentrated at medium
latitudes. Their long-term variability and their spatial distribution indicate
that they are distinct from the more persistent sources associated with the
nearby Gould Belt. They exhibit a large scale height of 1.3 +/- 0.6 kpc above
the Galactic plane. Potential counterparts for these sources include
microquasars accreting from a low-mass star and spewing a continuous jet.
Detailed calculations have been performed of the jet inverse Compton emission
in the radiation fields from the star, the accretion disc, and a hot corona.
Different jet Lorentz factors, powers, and aspect angles have been explored.
The up-scattered emission from the corona predominates below 100 MeV whereas
the disc and stellar contributions are preponderant at higher energies for
moderate (~15 deg) and small (~1 deg) aspect angles, respectively. Yet, unlike
in the high-mass, brighter versions of these systems, the external Compton
emission largely fails to produce the luminosities required for 5 to 10 kpc
distant EGRET sources. Synchrotron-self-Compton emission appears as a promising
alternative.Comment: 11 pages, 5 figures. Contributed paper to the "Multiwavelength
Approach to Unidentified Gamma-Ray Sources", Eds. K.S. Cheng & G.E. Romero,
to appear in Astrophysics and Space Science journa
Cryptanalysis of an image encryption scheme based on the Hill cipher
This paper studies the security of an image encryption scheme based on the
Hill cipher and reports its following problems: 1) there is a simple necessary
and sufficient condition that makes a number of secret keys invalid; 2) it is
insensitive to the change of the secret key; 3) it is insensitive to the change
of the plain-image; 4) it can be broken with only one known/chosen-plaintext;
5) it has some other minor defects.Comment: 10 pages, three figure
Molecular and Cellular Mechanisms of Delayed Fracture Healing in Mmp10 (Stromelysin 2) Knockout Mice
The remodeling of the extracellular matrix is a central function in endochondral ossification and bone homeostasis. During secondary fracture healing, vascular invasion and bone growth requires the removal of the cartilage intermediate and the coordinate action of the collagenase matrix metalloproteinase (MMP)-13, produced by hypertrophic chondrocytes, and the gelatinase MMP-9, produced by cells of hematopoietic lineage. Interfering with these MMP activities results in impaired fracture healing characterized by cartilage accumulation and delayed vascularization. MMP-10, Stromelysin 2, a matrix metalloproteinase with high homology to MMP-3 (Stromelysin 1), presents a wide range of putative substrates identified in vitro, but its targets and functions in vivo and especially during fracture healing and bone homeostasis are not well defined. Here, we investigated the role of MMP-10 through bone regeneration in C57BL/6 mice. During secondary fracture healing, MMP-10 is expressed by hematopoietic cells and its maximum expression peak is associated with cartilage resorption at 14 days post fracture (dpf). In accordance with this expression pattern, when Mmp10 is globally silenced, we observed an impaired fracture-healing phenotype at 14 dpf, characterized by delayed cartilage resorption and TRAP-positive cell accumulation. This phenotype can be rescued by a non-competitive transplant of wild-type bone marrow, indicating that MMP-10 functions are required only in cells of hematopoietic linage. In addition, we found that this phenotype is a consequence of reduced gelatinase activity and the lack of proMMP-9 processing in macrophages. Our data provide evidence of the in vivo function of MMP-10 during endochondral ossification and defines the macrophages as the lead cell population in cartilage removal and vascular invasio
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