197,859 research outputs found
Thermal model of water and CO activity of Comet C/1995 O1 (Hale-Bopp)
Full text linkAn investigation of the activity of Comet C/1995 O1 (Hale-Bopp) with a thermophysical nucleus
model that does not rely on the existence of amorphous ice is presented. Our approach incorporates
recent observations allowing to constrain important parameters that control cometary activity. The
model accounts for heat conduction, heat advection, gas diffusion, sublimation, and condensation in
a porous ice�dust matrix with moving boundaries. Erosion due to surface sublimation of water ice
leads to a moving boundary. The movement of the boundary is modeled by applying a temperature
remapping technique which allows us to account for the loss in the internal energy of the eroded surface
material. These kind of problems are commonly referred to as Stefan problems. The model takes
into account the diurnal rotation of the nucleus and seasonal effects due to the strong obliquity of
Hale-Bopp as reported by Jorda et al. (Jorda, L., Rembor, K., Lecacheux, J., Colom, P., Colas, F., Frappa,
E., Lara, L.M. [1997]. Earth Moon Planets 77, 167�180). Only bulk sublimation of water and CO ice are
considered without further assumptions such as amorphous ices with certain amount of occluded CO
gas. Confined and localized activity patterns are investigated following the reports of Lederer and
Campins (Lederer, S.M., Campins, H. [2002]. Earth Moon Planets 90, 381�389) about the chemical heterogeneity
of Hale-Bopp and of Bockel�©e-Morvan et al. (Bockel�©e-Morvan, D., Henry, F., Biver, N., Boissier,
J., Colom, P., Crovisier, J., Despois, D., Moreno, R., Wink, J. [2009]. Astron. Astrophys. 505, 825�
843) about a strong CO source at a latitude of 20. The best fit to the observations of Biver et al.
(Biver, N. et al. [2002]. Earth Moon Planets 90, 5�14) is obtained with a low thermal conductivity
of 0.01Wm1 K1. This is in agreement with recent results of the Deep Impact mission to 9P/Tempel
1 (Groussin, O., A�Hearn, M.F., Li, J.-Y., Thomas, P.C., Sunshine, J.M., Lisse, C.M., Meech, K.J., Farnham,
T.L., Feaga, L.M., Delamere, W.A. [2007]. Icarus 187, 16�25) and with previous thermal simulations
(K�¼hrt, E. [1999]. Space Sci. Rev. 90, 75â��82). The water production curve matches the production rates
well from 4 AU pre-perihelion to the outgoing leg while the model does not reproduce so well the
water production beyond 4 AU pre-perihelion. The CO production curve is a good fit to the measurements
of Biver et al. (2002) over the whole measured heliocentric range from 7 AU pre- to 15 AU
post-perihelion
Influence of low amounts of nanostructured silica and calcium carbonate fillers on the large-area dielectric breakdown performance of bi-axially oriented polypropylene
Full text linkInfluence of low amounts (1.0-2.0wt-%) of nanostructured silica and calcium carbonate fillers on the large area dielectric breakdown performance of bi-axially oriented polypropylene (BOPP) is analyzed. A multi-breakdown measurement method based on the self-healing breakdown capability of metallized film is utilized for the breakdown characterization in order to cover relatively large total film areas, thus leading to results of higher relevance from the practical point-of-view. The dispersion and distribution qualities of filler particles at the nanoscale are evaluated with transmission electron microscopy (TEM) imaging. Weibull statistical analysis suggests that the breakdown distribution homogeneity can be improved with both the filler types. The 1.0wt-% silica-BOPP composite also shows a shift of the weakest points towards higher dielectric strength in comparison to the neat BOPP. However, with increasing filler content, new failure modes are introduced into the nanocomposites, hence decreasing the overall breakdown performance in the >5% breakdown probability region in comparison to the un-filled reference BOPP film
Commercial BOPP film characterization
No full textDissertação de mestrado em Técnicas de Caracterização e Análise QuímicaO presente trabalho de experiência profissional ocorreu em ambiente industrial, descrevendo
passo a passo os procedimentos de controlo de qualidade do filme BOPP (Biaxially Oriented
PolyPropylene) na empresa Poligal, fornecedora de filmes BOPP, CPP (cast polipropileno) e metalizados
para distintas áreas de aplicação e para todo o globo.
O processo de produção do filme BOPP consiste num estiramento plano biaxial, ou seja, o
filme é orientado/estirado nas direções longitudinal e transversal. Este é um processo sequencial em
que se inicia com a matéria prima, polipropileno granulado, que sofre múltiplos estiramentos,
aquecimentos e arrefecimentos ao longo da sequência, finalizando-se com uma película de
polipropileno bobinada com todas as caraterísticas que o filme BOPP deve apresentar. Este processo
está dividido em distintas secções: silos, extrusão, chill roll, MDO (Machine Direction Orientation), TDO
(Transverse Direction Orientation), pull roll e winder, em que o filme sofre alterações em cada
segmento, aproximando-se do produto final.
Esta dissertação tem como principal objeto a caraterização de um filme BOPP comercial
segundo os procedimentos de controlo de qualidade da Poligal. Após a caraterização do filme
comercial com distintos ensaios, compilaram-se os resultados obtidos de modo a identificar o tipo de
filme BOPP, de acordo com os filmes que a empresa dispõe, e por fim compararam-se as
especificações da ficha de dados técnicos (TDS, technical data sheet) para o filme selecionado, com os
resultados obtidos do filme comercial.
Por fim, foi possível concluir que o filme BOPP comercial tem as características dos filmes para
embalagem flexíveis CATE 30 SOL, em que para os procedimentos: espessura, nível de tratamento,
propriedades mecânicas, retração, resistência à selagem térmica, temperatura de início de selagem e
coeficiente de atrito, há coerência de resultados com o especificado na TDS, exceto os ensaios de
opacidade/haze e brilho. Para estas propriedades, a especificação da TDS é para plástico virgens/não
manipulados sendo que o filme comercial além de manipulado já se encontrava como embalagem
interna envolvendo a “bolacha Maria” da marca Continente.The present work of professional experience took place in an industrial environment, describing
step by step the quality control procedures of BOPP (Biaxially Oriented PolyPropylene) film in the
company Poligal, supplier of BOPP, CPP (cast polypropylene) and metallized films for different
application for the entire globe.
The BOPP film production process consists of a biaxial plane stretching, that is, the film is
oriented/stretched in the longitudinal and transverse directions. This is a sequential process that starts
with the raw material, granulated polypropylene, which undergoes multiple stretching, heating and
cooling throughout the sequence, ending with a polypropylene film wound with all the characteristics
that BOPP film must present. This process is divided into different sections: silos, extrusion, chill roll,
MDO (Machine Direction Orientation), TDO (Transverse Direction Orientation), pull roll and winder, in
which the film undergoes changes in each segment, approaching the final product.
This dissertation has as main object the characterization of a commercial BOPP film according
to Poligal's quality control procedures. After characterizing the commercial film with different tests, the
results obtained were compiled in order to identify the type of BOPP film, according to the films that the
company has, and finally the specifications of the technical data sheet were compared (TDS, technical
data sheet) for the selected film, with the results obtained from the commercial film.
Finally, it was possible to conclude that the commercial BOPP film has the characteristics of
CATE 30 SOL flexible packaging films, in which for procedures: thickness, treatment level, mechanical
properties, shrinkage, resistance to thermal sealing, temperature of beginning of sealing and friction
coefficient, the results are consistent with those specified in the TDS, except for the opacity/haze and
gloss tests. For these properties, the TDS specification is for virgin/non-handled plastic, and the
commercial film, in addition to being handled, was already found as an internal packaging involving
“Maria cookie” from the Continente brand
"Plasmodium falciparum" transfection technology for the analysis of "var" gene regulation and knockout investigation
Full text linkMalaria is an infectious disease caused by protozoans of the genus
Plasmodium, which are injected by the bite of an infected female Anopheles
mosquito during a blood meal. Out of the four species that infect humans, P.
falciparum is the most important. About 40% of the world’s population is at
risk and 500 million cases of malaria occur every year, mainly in sub-
Saharan Africa. Due arising resistance of mosquitoes against insecticides,
the lack of a malaria vaccine, and emerging resistance of parasites against
established drugs, research into new drugs and vaccine targets is most
important.
Morbidity is associated with adherence of infected red blood cells (iRBC) to
endothelial tissue thereby obstructing the blood flow. The major protein
conferring this cytoadherence is the P. falciparum erythrocyte membrane
protein 1 (PfEMP1) anchored in the erythrocyte membrane of infected red
blood cells (iRBCs). PfEMP1 is encoded by the var gene family that consists
of approximately 60 members in the haploid genome of the 3D7 strain. var
genes are expressed mutually exclusive, i.e. only one var gene is expressed
in a parasite at a time and the rest is silenced. In this thesis we were
interested in the regulation of expression and silencing of var genes. For this
purpose we generated transgenic parasite lines that harbored plasmids
expressing luciferase under the control of various fragments of the var gene
upstream region. By comparing luciferase activities in the different lines we
identified the core promoter, two activator-binding sites and a repressorbinding
site. Additionally, we identified a regulatory sequence on the var
upstream region that interacts with the var intron during silencing. Using
quantitative RT-PCR with specific primers for every var gene we were unable
to confirm that the var upstream regions on the transfected plasmids were
recognized by the machinery that ensures mutually exclusive transcription.
In the second part of this thesis, we evaluated phosphodiesterase 1 (PDE1)
as a possible drug target in P. falciparum by creating a knockout parasite
line. PDEs are known drug targets in humans where selective PDE inhibitors
are being used to treat a wide range of diseases. In trypanosomiasis
research PDE inhibitors are promising drug candidates against sleeping
sickness, Nagana or Chagas’ disease. Out of the four PDEs described for P.
falciparum we focused on PfPDE1, which is expressed in blood stage
parasites and in gametocytes and sporozoites. We observed a slightly faster
growth of the knockout parasite line compared to the wildtype indicating that
the knockout parasite had a shorter erythrocytic lifecycle. We found that
PfPDE1 is responsible for 20% of the total cGMP activity observed in late
blood stage parasites and that there is no rescue mechanism of the
remaining PDEs to compensate for the loss of activity. We were not able to
localize PfPDE1 in the parasite. The fact that we could delete PfPDE1 clearly
shows that it is not an essential gene in blood stage forms of P. falciparum
and hence not a good drug target. Nevertheless we created a useful tool to
investigate the role of PfPDE1 in the development of sexual parasite forms
Small-body encounters using solar sail propulsion
No full textCometary Rendezvous and Flybys have large V requirements, which impose almost unattainable, and sometimes prohibitive, demands on the propellant budget of conventional, chemical propulsion. Ion Propulsion is a viable alternative, but as the number and difficulty of target objectives increases then the potential of this technology becomes rapidly less attractive. Solar sails exhibit an extremely high effective specific impulse over long mission durations. No propellant is required so that large changes in V could be realised without necessitating the introduction of complex gravity assists, which prolong mission duration and restrict launch opportunities. The endurance of the structures and materials are thus the only limiting factors dictating the number and range of bodies with which the solar-sail propelled vehicle can encounter throughout its lifetime. In this paper we have analysed a number of high-energy, small-body mission scenarios using a parameterised approach to sail control representation. The sail cone and clock angle histories were characterised by linear interpolation across a set of discrete nodes. The optimal control problem was thus transcribed to a Non-Linear Programming problem to select the optimal controls at the nodes that minimised the transfer time while enforcing the cartesian end-point boundary constraints (6 states for rendezvous, 3 for flypast). The Fortran77 optimisation package NPSOL 5.0 was used for this purpose with the variational equations of motion formulated in modified equinoctial orbital elements and integrated using a variable-order, adaptive step-size Adams-Moulton-Bashforth method. We present optimal rendezvous trajectories to Short-Period Comets such as 46P/Wirtanen in 484 days with a sail characteristic acceleration of 1.9 mms-2, and with 2P/Encke in 574 days with a characteristic acceleration of 1.0 mms-2. An analysis using high-performance sails has been conducted to permit fast flyby intercepts of newly discovered Long Period Comets (LPCs). Previous examples adopted were C/1995 O1/Hale- Bopp, C/1995 Y1/Hyakutake, C/1999 T1/McNaught-Hartley, C/1999 F1/Catalina, C/1999 N2/Lynn and C/1999 H1/Lee, to demonstrate the feasibility of a late launch to quickly intercept a new LPC using a solar sail. Since the time between discovery of a new LPC such as Hale-Bopp and perihelion passage was less then 2 years, this then leaves a very short time-span for orbit determination, preparation, planning and operational phases. Preliminary mission analysis shows that a Hale-Bopp perihelion flypast could have been achieved, with a sail characteristic acceleration of 5.0 mms-2, by launching just 209 days before comet perihelion passage. With a characteristic acceleration of 2.0 mms-2 Hale-Bopp could also have been intercepted at its descending node by launching 270 days before nodal descent. The sail could then have returned to rendezvous with the Earth 261 days later, giving a minimum total mission turn-around time of 531 days. An alternative, dual flyby scenario has been investigated, to continue on to C/1997 D1/Mueller, after which solar system escape was reached and arrival at Heliopause would occur in 12 years. Solar Electric Propulsion has been adopted as the primary propulsion system for the DAWN dual asteroid rendezvous mission scheduled for launch in 2006. The objective of this mission is to rendezvous with inner main-belt asteroids, Vesta and Ceres. We have also investigated solar sail adaptation to this mission, for the same launch date and 11 month orbiter stay-times. We have extended the mission objectives to two further asteroids, Lucina and Lutetia, with the aim of demonstrating a Mainbelt Asteroid Survey scenario
Frozen to death? Detection of comet Hale-Bopp at 30.7 AU
Full text linkContext. Comet Hale-Bopp 9C/1995 O1) has been the most interesting comet ever encountered by modern astronomy, which continued to display significant activity at a solar distance of 25.7 AU. It is unclear when and how this activity will finally cease. Aims. We present new observations with the ESO 2.2 m telescope at La Silla to monitor the activity of Hale-Bopp at 30.7 AU solar distance. Methods. On 2010-12-04, 26 CCD images were taken with 180 s exposure times for photometry and morphology. Results. The comet was detected in R and had a total brightness of 23(m).3 +/- 0(m).2, which corresponds to an absolute brightness of R(1, 1, 0) = 8(m).3. The profile of the coma was star-like at a seeing of 1 ''.9, without any evidence of a coma or tail extending farther than 2 ''.5 (= 55 000 km in projection) and exceeding 26.5 mag/arcs(2) surface brightness. The measured total brightness corresponds to a relative total reflecting surface, a(R)C, of 485 km(2), nine times less than three years before. The calculated a(R)C value would imply a nucleus with 60-65 km radius assuming 4% albedo. This size estimate contradicts significantly the previous results scattering around 35 km. Conclusions. We propose that the comet may still be in a low level of activity, despite the lack of a prominent coma. Alternatively, if the nucleus is already dormant, the albedo should be as high as 13%, assuming a radius of 35 km. With this observation, Hale-Bopp has become the most distant comet ever observed, far beyond the orbit of Neptune.Hungarian OTKA K76816, K83790, MB08C 81013Hungarian Academy of SciencesEotvos Fellowship of the Hungarian StateAstronom
Notice bibliographique de M. Franz Bopp, élu associé étranger de l'Académie
No full textNotice bibliographique de M. Franz Bopp, élu associé étranger de l'Académie. In: Comptes rendus des séances de l'Académie des Inscriptions et Belles-Lettres, 2ᵉ année, 1858. pp. 414-417
- …
