Zylon ber wound around every layer of copper wire. The magnetic pressure in the magnet during the pulse is compensated by the mechanical resistance of the coil and its reinforcement. A shot at the maximum eld increases the coil temperature from 77 K (boiling temperature of nitrogen) to about 300 K due to Joule eect. Temperatures higher than 300 K reduce the mechanical resistance of the materials and increase the electrical resistance of the coil with risk of damage. After a pulse the nitrogen bath cools down the magnet to reach the desired values of temperature and resistance. The cooling can take longer than one hour. Figure 4.10 oers an overview of the temporal prole of the available magnets and reports also the energy required to obtain the maximal magnetic eld and the diameter of the inner bore. The diameter is reduced if an additional inner cryostat is needed to perform experiments at a temperature dierent from that of liquid nitrogen; in our experiment with rubidiumvapors is crucial to work at room temperature in order to have a sucient atomic vapor density to observe a signal.
Chapter 4 Carbon nanotubes inhighmagneticfields
unexpected because, as it also follows from our absorption measurements, we are not supposed to observe a modiﬁcation of the bandgap energy when the magnetic ﬁeld is not parallel to the tube axis. In addition to this observation, Mortimer et al. identify an unexpected tube diameter dependence of this eﬀect, i.e. the dark and bright exciton splitting decreases with increasing tube diameter although the in- verse is expected. The authors attribute this behaviour to the role of the spin and to the closeness of the lowest lying singlet and highest triplet state [ Mortimer 2007b ]. Changes in the spectrum of our experiment become only signiﬁcant in the Voigt conﬁguration with light polarised parallel to the magnetic ﬁeld and to the tube axis (solid red line in ﬁgure 4.7c). We clearly observe a decrease in absorption and a broadening of the peak. To double check our ﬁndings in absorption spec- troscopy we have added an inset in ﬁgure 4.7c with the photoluminescence response of the sample in absence and at highmagnetic ﬁeld (55 T) in Voigt conﬁgura- tion and parallel polarisation. The traces are normalised by the zero-ﬁeld inten- sity of the dominant (6, 5) peak. We note strong intensity increase and a clear red shift with respect to the initial position, observed in many experiments be- fore [ Shaver 2007b , Mortimer 2007a ].
Motivated by this challenging open question, we performed NMR experiments on a high-quality LiCuVO 4 single crystal in pulsed magneticfields
up to 55 T providing access to the saturation fields not only for H k c, but also for the perpendicular, H k b, orientation. Our measurements of the NMR line position and width allow for a very precise determination of the field dependence of the local distribution of the magnetization near H sat . The spin-nematic state is a homogeneous, field-dependent, longitudinal spin state without any transverse dipolar order, thus corresponding to a field-dependent NMR line position without any change of its width with respect to the saturated phase. Our NMR results in LiCuVO 4 , together with the bulk
doing the neutron diffraction experiments. The magnetiza- tion in phase II equals approximately one third of the saturated value above 50 T, once a linear contribution of Pauli or Van Vleck paramagnetism has been subtracted from the magnetization. Neutron diffraction experiments were performed using the thermal neutron three-axis spec- trometer IN22 located at the Institut Laue-Langevin, Grenoble. Incident neutrons of wavelength ¼ 1:53 A were selected using a pyrolytic graphite (PG) monochro- mator. After the monochromator, a PG filter was placed for reducing the higher-order contamination of neutrons. The scattered neutrons were detected in the two-axis mode without an analyzer. The high-field experiments were done in two scattering geometries. In the first setting, the sample was set to a small magnet coil, and it was mounted in the 4 He cryostat with the c and a axes in the horizontal
formula to interpret resistivity ρ = m/ne 2 τ, where τ is the scattering rate, m and e are the
mass and electric charge of electron respectively and n is the density of electrons.
More than two decades ago it was discovered that the temperature dependence of resistivity deviates from linearity . The point below which resistivity is not linear and it shows either a downturn in YBCO  or an upturn in Nd-LSCO  is known as the onset of the pseudogap—T*. Here we only focus on the upturn of pseudogap for Nd-LSCO. Resistivity depends on the number of carriers and scattering (elastic and inelastic). When the pseudogap appears, the density of states, the carrier density and the inelastic scattering all decrease (and the decrease in the magnitude of one may or may not be the consequence of a decrease in another). In a clean system such as YBCO, when the pseudogap opens, as the dominant source of scattering is the elastic scattering, the inelastic scattering decreases which results in a decrease in resistivity. But in a dirty system like Nd-LSCO, when the pseudogap, the inelastic scattering does not change that much as it is dominant, so, as there are fewer carriers in the system, the resistivity rises.
value of r C 0 has only a small effect on the chemotactic velocity ( S3e and S3f Fig ), we used the
limiting case of τ run for r C 0 � 0 in these simulations. Finally, the run times change along the
course of a bacterial trajectory, because the run times (or the reversal rates) are dependent on the oxygen gradient as well as the oxygen concentration, the latter because in (magneto-)aero- taxis, oxygen acts as an attractant at low concentrations but as a repellent at high concentra- tions (see ref. [ 12 ]). In our simulations, the duration of a run is decided by the local oxygen concentration and oxygen gradient at the beginning of a run, thus changes within a run are neglected. This is unproblematic, because the oxygen profile changes slowly on the length scale of a run. There is however, one exception: In our simulations of magneto-aerotactic band formation, when a bacterium crosses the preferred oxygen concentration, the run times change drastically because of the reversed bias as oxygen switches from an attractant to a repel- lent. Therefore, in this situation the change of the run time during the run has to be included. This is implemented by starting a new run in the same direction when crossing the preferred concentration (implementing an instantaneous change in the reversal rate). Without this, unrealistically broad bands form (see S4 Fig ), as the bacteria ‘overshoot’ in the unfavorable direction, while the change in the reversal rate results in shorter runs, reducing band width.
dio flux. De Becker & Raucq (2013) recently provided the most up-to-date catalog of such systems.
High angular resolution observations of some PACWB have allowed to disentangle the thermal and non-thermal emissions (e.g. OB2 #5, Dzib et al. 2013) and showed that the synchrotron emission is associated to the wind-wind interaction region. This region is also a source of thermal X-rays, in addition to the in- trinsic X-ray emission produced in the stellar winds of the indi- vidual components. The X-ray spectrum produced in the wind interaction region is generally significantly harder than that of massive single stars, and the X-ray emission is variable with the orbital phase (e.g. De Becker et al. 2011; Cazorla et al. 2014).
OCIS codes: (120.0120) Instrumentation, measurement, and metrology ; (060.3735) Fiber Bragg Gratings
Shock physics intensively uses numerical modelings relying on equations of state (EOS) of materials and thermodynamical parameters obtained by mechanical testing (e.g. shock impact experiments in launchers). As an alternative, large strain (up to 1.5) and high strain rates (up to 10 5 s -1 for ductile materials) may be reached in metallic samples under application of a magnetic pressure. High pulse powers (HPP, 10-100 GW) are generated by intense pulse currents (3-5 MA) applied at high-frequency (50 kHz - 500 kHz). The pressure resulting from the Laplace force scales by the square of the current in the range [1 - 100 GPa].
A. Films with electric or magnetic losses
Two types of microwave sensing films are used, either with electric or magnetic losses. These films have initially been developed for EMIR method. EMIR consists in imaging the electromagnetic field through the infrared emission of a thin film located in the field and heated by it. These thin films are polymer foils with small conductivity for electric field imaging or with ferromagnetic losses for magnetic film imaging. For the fluorescent EMVI method, the same films are coated with fluorescent molecules, as presented in the next section.
We perform saturated absorption spectroscopy on the D 2 line for room temperature rubidium
atoms immersed inmagneticfields within the 0.05-0.13 T range. At those medium-high field values the hyperfine structure in the excited state is broken by the Zeeman effect, while in the ground state hyperfine structure and Zeeman shifts are comparable. The observed spectra are composed by a large number of absorption lines. We identify them as saturated absorptions on two-level systems, on three-level systems in a V configuration and on four-level systems in a N or double-N configuration where two optical transitions not sharing a common level are coupled by spontaneous emission decays. We analyze the intensity of all those transitions within a unified simple theoretical model. We concentrate our attention on the double-N crossovers signals whose intensity is very large because of the symmetry in the branching ratios of the four levels. We point out that these structures, present in all alkali atoms at medium-highmagneticfields, have interesting properties for electromagnetically induced transparency and slow light applications.
2 Jordan et al.
Magneticfields are found to occur in a wide variety of stars, including pre-main se- quence T Tau stars and Herbig AeBe stars, upper main sequence O, B and A stars, rapidly rotating and active lower main sequence stars, AGB stars, white dwarfs, and neutron stars. Main sequence stars with effective temperatures below 7000 K have spa- tially complex magneticfields and are thought to be generated by current dynamos operating in the outer convective layer. Hotter stars generally reveal fieldsin only a fraction of any stellar type, and the fields appear simple in structure. Such static fields are usually thought to be fossil fields, frozen into the star by the very high electrical conductivity and originating from earlier stages of the star’s evolution.
To acknowledge with precision all the people who contributed to this work or supported me by their affection during those three years is maybe the most difficult part of this manuscript. Therefore I will just try to be qualitative and not as rigorous as I intended to be in the following scientific part. This being said, and speaking about quality, my first acknowledgment is for my PhD supervisor Joao Santos. Qualities he has a lot, and one of them is that he is trustful! He trusted me from the beginning, giving me this opportunity to make a thesis in a field where I started completely from scratch (I did not even know what was a plasma). All along those three years he also handled my strong personality and found how to drive me as a better scientist and also a better man! He will stay as a friend and mentor in my future life after this PhD. Then I think to all other colleagues who participated or not in this work, and to name a few: Dimitri Batani, Vladimir Tikhonchuk, Michael Ehret, Alexandre Poyé, Lorenzo Giuffrida, Claudio Bellei, Michael Touati, Mokrane Hadj-Bachir, Alessio Morace, Pierre Forestier-Colleoni, ... (I realize here that if I wanted to be precise, this part would extend over a few pages). I want also to thanks all people of CELIA who gave me strength in coffee breaks, notably, and some people who made also my work easier: Sophie Heurtebise, Céline Oum, Sonia Senut and Emmanuelle Lesage, always here to solve my travel issues, among other administrative things! I also want to thanks my referees who are already, and rightly so, presented in the cover page. They worked a lot to read this long thesis and provide me exhaustive corrections and suggestions. They also appreciated my work and I found myself very proud of their nice comments and wish only that one day I could be a researcher as talented as they are. Then I want to finish this part giving a thanks to all my collaborators and people I met during conferences and experiments, I have a lot of good memories of travels and meetings with people always nice and welcoming! To resume, I had a lot of luck! Now I will switch to French to thanks my family and other friends who would certainly prefer to read me in my mother-tongue.
tangi Roussel 1 , Lucio Frydman 2 , Denis Le Bihan 1 & Luisa Ciobanu 1
Blood oxygenation level dependent (BoLD) functional magnetic resonance imaging (fMRI) indirectly measures brain activity based on neurovascular coupling, a reporter that limits both the spatial and temporal resolution of the technique as well as the cellular and metabolic specificity. Emerging methods using functional spectroscopy (fMRS) and diffusion-weighted fMRI suggest that metabolic and structural modifications are also taking place in the activated cells. This paper explores an alternative metabolic imaging approach based on Chemical exchange saturation transfer (Cest) to assess potential metabolic changes induced by neuronal stimulation in rat brains at 17.2 T. An optimized CEST- fMRI data acquisition and processing protocol was developed and used to experimentally assess the feasibility of glucoCEST-based fMRI. Images acquired under glucose-sensitizing conditions showed a substantial negative contrast that highlighted the same brain regions as those activated with BoLD- fMRI. We ascribe this novel fMRI contrast to CEST’s ability to monitor changes in the local concentration of glucose, a metabolite closely coupled to neuronal activity. Our findings are in good agreement with literature employing other modalities. The use of CEST-based techniques for fMRI is not limited to glucose detection; other metabolic pathways involved in neuronal activation could be potentially probed. Moreover, being non invasive, it is conceivable that the same approach can be used for human studies.
However, the heat released by magnetic NPs does not depend only on their intrinsic properties but also on dipolar magnetic interaction between individual NPs building up as the concentration increases.[66,67] The effect that dipolar interactions might have on SAR is not completely understood at present and has often not been properly addressed in the past years.[62,68,69] Experimental studies reported either a decrease or an increase of SAR with interactions.[62,66–68,70,71] In fact, depending on the NP anisotropy K a , dipolar interactions may act differently on the clustering/spatial arrangement of NPs under an applied magnetic field leading either to their aggregation or to their alignment in chains. A very recent evaluation of these interaction effects [62,68] and studies on magnetosomes synthesized by bacteria[57,58] pointed out that chains of ferromagnetic NPs are ideal candidates for obtaining high SAR values, introducing a coercivity field and opening a “square hysteresis”. Furthermore, the cubic shape of NPs would favor the NPs geometrical arrangement compared to the spherical shape. Indeed chains of nanocubes can form due to the existence of strongly anisotropic dipolar forces mediating nanoparticle attachment.[62,68] Serantes et al. reported the positive effect of oriented attachment of 44 nm NPs on hyperthermia properties. The formation of chains with core-shell nanocubes at low concentration was observed by TEM without applying any magnetic field. These observations may thus explain the high SAR values obtained at low concentration with these nanocubes by contrast to values obtained at high concentration. Indeed at high concentration, aggregates form due to enhanced dipolar interactions and then the benefit effects of the geometric arrangement is lost. Thus MH by using iron oxide based NPs is quite complex as it depends on NP materials properties but also on dipolar interaction between them, and on the magnitude and frequency of the applied AMF which are limited by the MH equipment. Nevertheless, there are currently designed magnetic NPs (nanocubes, nanoflowers, core- shells....) with optimized MH properties in conditions compatible with clinical uses. Therefore the existence of suitable magnetic nanoheaters is promising for the release of drug triggered by locally deposited heat, itself generated internally by MH, a strategy sometimes referred to as “magneto-chemotherapy”.
seem easy to solve the Cauchy problem inmagnetic Sobolev spaces of high degree. To overcome this difficulty, we work as in ,  and approximate the solution of (1.1) by solution of a non-linear Schr¨odinger equation with non-linearity linearized at infinity. In the work of Cazenave and Weissler, the main tool to justify the approximation is an energy conservation. In our case, the Hamiltonian depends on time, so that the energy is not conserved. Nevertheless, the error term is controled by the H 1
a description of the magnetic field of the superconductor can- not disregard the penetration of vortices and their movement inside the material. Several experiments of magnetic shielding have been carried out in the last years, using both low-Tc and high-Tc superconducting materials operating in the mixed state. In this state, the interpretation of the experimental results requires to calculate the flux lines distribution inside and outside the sample. One needs models such as the critical state model 8 – 10 associated with a constitutive law giving the non-linear dependence of the electric field on the current den- sity to account for the energy dissipation due to vortex motion. 7 , 11 , 12 Because of this complexity, this approach yields exact solution only in few idealized cases. 13
The magnetic field of the laptop battery shown in figure 4 is clearly the field induced by a direct current. The absolute value remains between the borders of 34 and 36 µT, the high-frequency share can be attributed to the measurement noise. As the Y-component is constant, the slight changes in the x- and z-component are most likely to be caused by an external source. On the contrary, figure 5 looks very different. It shows the magnetic field of a laptop PSU, containing a transformer and a rectifier. The magnetic field, both absolute value and component-wise, is characterised by a pulsed course resulting from short charging phases. In these phases the field is oscillating because the measurements were taken at the AC supply side of the PSU. The filament lamp, which is also supplied with alternating cur- rent, creates a similar field depicted in figure 6. But, it is continuously alternating, that is to say the magnetic field does not have an additional overlaid time-course profile. The time section was chosen very small in order to reveal the oscillations ; it should be noted that measurements over a wider time span have beats.
model with an age of 28.4 Myr, a radius of 3.39 R , an e ffec-
tive temperature of 17 800 K, a central hydrogen mass fraction
of 0.54, and solar-like metallicity, P +19 concluded that mag- netic frequency shifts significantly change if rotation is taken into account using the TAR, and that a magnetic field with a near-core field strength of 150 kG would be detectable in period spacing patterns of high-radial-order g modes. Even though the magnetic influence is found to be significant for modes of higher radial order, it remains perturbative, and the magnetic frequency shifts are too small to be detected using 150 d of CoRoT photom- etry ( P +19 ). However, P +19 only considered one stellar model and a small range of magnetic field strengths. A natural exten- sion to their work consists of investigating the influence of stellar parameters and large variations of magnetic field strength on the derived period spacing patterns.