118,560 research outputs found
Thermal model of water and CO activity of Comet C/1995 O1 (Hale-Bopp)
No full textAn 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
No full textInfluence 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
"Plasmodium falciparum" transfection technology for the analysis of "var" gene regulation and knockout investigation
No full textMalaria 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
EXISTENCE AND ASYMPTOTIC BEHAVIOR OF SOLUTIONS TO EIGENVALUE PROBLEMS FOR SCHRÖDINGER-BOPP-PODOLSKY EQUATIONS
No full textWe study the existence and multiplicity of solutions for the Schrödinger-Bopp-Podolsky system (formula presented) where Ω is an open bounded and smooth domain in R3, a > 0 is the Bopp-Podolsky parameter. The unknowns are u, φ: Ω → R and ω ∈ R. By using variational methods we show that for any a > 0 there are infinitely many solutions with diverging energy and divergent in norm. We show that ground states solutions converge to a ground state solution of the related classical Schrödinger-Poisson system, as a → 0
Influence of solar photogravitation on the motion of comet Hale-Bopp
No full textOn the basis of photogravitational theory, the influence of solar photogravitation on the motion of comet Hale-Bopp is discussed. It is shown that for plasma tail of comet Hale-Bopp there is only one collinear point L-3 and for a few of dust tail there can be two coplanar points L-6, L-7 and three collinear points L-21, L-22, L-3. The regions in which the coplanar points exist and the dust grain of comet Hale-Bopp can move are also obtained
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
Modified Scattering for the Schr\"odinger-Bopp-Podolsky Equation
No full textWe prove sharp decay and modified scattering for the
Schr\"odinger-Bopp-Podolsky equation in and spatial dimensions with
small initial data chosen from a weighted Sobolev space.Comment: 17 pages, comments welcome
Un’analisi contrastiva nella Zergliederung di Franz Bopp: la radice tra indoeuropeo e semitico
No full textQuesto lavoro prende in considerazione lo sviluppo dell'idea di 'radice' nell'opera di Franz Bopp, mettendo in risalto il ruolo che la comparazione sistematica tra l'ambito linguistico indoeuropeo e l'ambito linguistico semitico ha svolto nella sua definizione. Sulla scorta di due importanti studi di Jean Rousseau, si sottolinea come il paragone sistematico dello statuto delle radici nelle due famiglie linguistiche, ampiamente documentato nelle opere di Bopp, abbia costituito al contempo un punto di arrivo nella riflessione sulla radice nelle lingue semitiche e un punto di partenza per la definizione della radice nelle lingue indoeuropee.This paper takes into account the development of the idea of 'root' in the work of Franz Bopp, highlighting the role that the systematic comparison between the Indo-European linguistic field and the Semitic linguistic field played in its definition. On the basis of two important studies by Jean Rousseau, it is stressed that the systematic comparison of the status of roots in the two language families, which is widely documented in Bopp's works, constituted both a point of arrival in the reflection on the root in Semitic languages and a starting point for the definition of the root in Indo-European languages
Bopp–Podolsky black holes and the no-hair theorem
No full textAbstract Bopp–Podolsky electrodynamics is generalized to curved space-times. The equations of motion are written for the case of static spherically symmetric black holes and their exterior solutions are analyzed using Bekenstein’s method. It is shown that the solutions split up into two parts, namely a non-homogeneous (asymptotically massless) regime and a homogeneous (asymptotically massive) sector which is null outside the event horizon. In addition, in the simplest approach to Bopp–Podolsky black holes, the non-homogeneous solutions are found to be Maxwell’s solutions leading to a Reissner–Nordström black hole. It is also demonstrated that the only exterior solution consistent with the weak and null energy conditions is the Maxwell one. Thus, in the light of the energy conditions, it is concluded that only Maxwell modes propagate outside the horizon and, therefore, the no-hair theorem is satisfied in the case of Bopp–Podolsky fields in spherically symmetric space-times
Satellite data reveal earlier and stronger phytoplankton blooms over fronts in the Gulf Stream region: code and data
No full textSoftware used to conduct the analyses detailed in "Satellite data reveal earlier and stronger phytoplankton blooms over fronts in the Gulf Stream region", by Haëck C., Lévy M., Mangolte I., and Bopp L., submitted to Biogeosciences in December 2022.
This repository also includes some documentation and the necessary data to produce the figures of the same article.
The latest version can be found at https://gitlab.in2p3.fr/clement.haeck/submeso-color
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