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Search Results: 1 - 10 of 6335 matches for " Nicolas Jaccard "
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Investigations of Optical Coherence Properties in an Erbium-doped Silicate Fiber for Quantum State Storage
Matthias U. Staudt,Sara R. Hastings-Simon,Mikael Afzelius,Didier Jaccard,Wolfgang Tittel,Nicolas Gisin
Physics , 2006, DOI: 10.1016/j.optcom.2006.05.007
Abstract: We studied optical coherence properties of the 1.53 $\mu$m telecommunication transition in an Er$^{3+}$-doped silicate optical fiber through spectral holeburning and photon echoes. We find decoherence times of up to 3.8 $\mu$s at a magnetic field of 2.2 Tesla and a temperature of 150 mK. A strong magnetic-field dependent optical dephasing was observed and is believed to arise from an interaction between the electronic Er$^{3+}$ spin and the magnetic moment of tunneling modes in the glass. Furthermore, we observed fine-structure in the Erbium holeburning spectrum originating from superhyperfine interaction with $^{27}$Al host nuclei. Our results show that Er$^{3+}$-doped silicate fibers are promising material candidates for quantum state storage.
Microfabricated Modular Scale-Down Device for Regenerative Medicine Process Development
Marcel Reichen, Rhys J. Macown, Nicolas Jaccard, Alexandre Super, Ludmila Ruban, Lewis D. Griffin, Farlan S. Veraitch, Nicolas Szita
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0052246
Abstract: The capacity of milli and micro litre bioreactors to accelerate process development has been successfully demonstrated in traditional biotechnology. However, for regenerative medicine present smaller scale culture methods cannot cope with the wide range of processing variables that need to be evaluated. Existing microfabricated culture devices, which could test different culture variables with a minimum amount of resources (e.g. expensive culture medium), are typically not designed with process development in mind. We present a novel, autoclavable, and microfabricated scale-down device designed for regenerative medicine process development. The microfabricated device contains a re-sealable culture chamber that facilitates use of standard culture protocols, creating a link with traditional small-scale culture devices for validation and scale-up studies. Further, the modular design can easily accommodate investigation of different culture substrate/extra-cellular matrix combinations. Inactivated mouse embryonic fibroblasts (iMEF) and human embryonic stem cell (hESC) colonies were successfully seeded on gelatine-coated tissue culture polystyrene (TC-PS) using standard static seeding protocols. The microfluidic chip included in the device offers precise and accurate control over the culture medium flow rate and resulting shear stresses in the device. Cells were cultured for two days with media perfused at 300 μl.h?1 resulting in a modelled shear stress of 1.1×10?4 Pa. Following perfusion, hESC colonies stained positively for different pluripotency markers and retained an undifferentiated morphology. An image processing algorithm was developed which permits quantification of co-cultured colony-forming cells from phase contrast microscope images. hESC colony sizes were quantified against the background of the feeder cells (iMEF) in less than 45 seconds for high-resolution images, which will permit real-time monitoring of culture progress in future experiments. The presented device is a first step to harness the advantages of microfluidics for regenerative medicine process development.
Controlled Stark shifts in Er$^{3+}$-doped crystalline and amorphous waveguides for quantum state storage
Sara R. Hastings-Simon,Matthias U. Staudt,Mikael Afzelius,Pascal Baldi,Didier Jaccard,Wolfgang Tittel,Nicolas Gisin
Physics , 2006, DOI: 10.1016/j.optcom.2006.05.003
Abstract: We present measurements of the linear Stark effect on the $^{4}$I$_{15/2} \to$ $^{4}$I$_{13/2}$ transition in an Er$^{3+}$-doped proton-exchanged LiNbO$_{3}$ crystalline waveguide and an Er$^{3+}$-doped silicate fiber. The measurements were made using spectral hole burning techniques at temperatures below 4 K. We measured an effective Stark coefficient $(\Delta\mu_{e}\chi)/(h)=25\pm1$kHz/Vcm$^{-1}$ in the crystalline waveguide and $(\bar{\Delta\mu_{e}}\chi)/(h)=15\pm1$kHz/Vcm$^{-1}$ in the silicate fiber. These results confirm the potential of Erbium doped waveguides for quantum state storage based on controlled reversible inhomogeneous broadening.
Probing the phase diagram of CeRu_2Ge_2 by thermopower at high pressure
H. Wilhelm,D. Jaccard
Physics , 2004, DOI: 10.1103/PhysRevB.69.214408
Abstract: The temperature dependence of the thermoelectric power, S(T), and the electrical resistivity of the magnetically ordered CeRu_2Ge_2 (T_N=8.55 K and T_C=7.40 K) were measured for pressures p < 16 GPa in the temperature range 1.2 K < T < 300 K. Long-range magnetic order is suppressed at a p_c of approximately 6.4 GPa. Pressure drives S(T) through a sequence of temperature dependences, ranging from a behaviour characteristic for magnetically ordered heavy fermion compounds to a typical behaviour of intermediate-valent systems. At intermediate pressures a large positive maximum develops above 10 K in S(T). Its origin is attributed to the Kondo effect and its position is assumed to reflect the Kondo temperature T_K. The pressure dependence of T_K is discussed in a revised and extended (T,p) phase diagram of CeRu_2Ge_2.
Calorimetric and transport investigations of CePd_{2+x}Ge_{2-x} (x=0 and 0.02) up to 22 GPa
H. Wilhelm,D. Jaccard
Physics , 2002, DOI: 10.1103/PhysRevB.66.064428
Abstract: The influence of pressure on the magnetically ordered CePd_{2.02}Ge_{1.98} has been investigated by a combined measurement of electrical resistivity, $\rho(T)$, and ac-calorimetry, C(T), for temperatures in the range 0.3 K
Adaptation of the Bridgman anvil cell to liquid pressure mediums
A. -S. Ruetschi,D. Jaccard
Physics , 2008, DOI: 10.1063/1.2818788
Abstract: The advantage of Bridgman anvil pressure cells is their wide pressure range and the large number of wires which can be introduced into the pressure chamber. In these pressure cells soft solid pressure mediums like steatite are used. We have succeeded in adapting the Bridgman cell to liquid pressure mediums. With this breakthrough it is now possible to measure in very good hydrostatic pressure conditions up to 7 GPa, which is about twice the pressure attainable in piston-cylinder cells. The pressure gradient in the cell, estimated from the superconducting transition width of lead, is reduced by a factor of five in the liquid medium with respect to steatite. By the use of non-magnetic materials for the anvils and the clamp and due to the small dimensions of the latter, our device is specially suitable for magneto-transport measurements in dilution fridges. This pressure cell has been developed to measure very fragile and brittle samples like organic conductors. Resistivity measurements of (TMTTF)2BF4 performed in a solid and liquid pressure medium demonstrate the necessity of hydrostatic pressure conditions for the study of organic conductors at high pressures.
Spin and Valence-Fluctuation Mediated Superconductivity in Pressurized Fe and CeCu2(Si/Ge)2
D. Jaccard,Alexander T. Holmes
Physics , 2004,
Abstract: We review the evidence supporting valence-fluctuation mediated superconductivity in CeCu2Si2 and CeCu2Ge2, where Tc reaches 2.4 K at high pressure. In these systems the valence and magnetic critical points, at p_V and p_c respectively, are well separated. Characteristic signatures associated with both phenomena are distinct. In contrast, the valence and spin fluctuation regions appear much closer in most Ce based compounds. Concerning d-transition metals, superconductivity in pure iron emerges in the pressure window 15-30 GPa with the onset of Tc up to almost 3 K. All relevant observations point to unconventional superconductivity, likely mediated by ferromagnetic spin fluctuations.
Valence fluctuation mediated superconductivity in CeCu2Si2
Alexander T. Holmes,Didier Jaccard
Physics , 2005, DOI: 10.1016/j.physb.2006.01.123
Abstract: It has been proposed that there are two types of superconductivity in CeCu2Si2, mediated by spin fluctuations at ambient pressure, and by critical valence fluctuations around a charge instability at a pressure P_v \simeq 4.5 GPa. We present in detail some of the unusual features of this novel type of superconducting state, including the coexistence of superconductivity and huge residual resistivity of the order of the Ioffe-Regel limit, large and pressure dependent resistive transition widths in a single crystal measured under hydrostatic conditions, asymmetric pressure dependence of the specific heat jump shape, unrelated to the resistivity width, and negative temperature dependence of the normal state resistivity below 10 K at very high pressure.
On the thermoelectricity of correlated electrons in the zero-temperature limit
Kamran Behnia,Didier Jaccard,Jacques Flouquet
Physics , 2004, DOI: 10.1088/0953-8984/16/28/037
Abstract: The Seebeck coefficient of a metal is expected to display a linear temperature-dependence in the zero-temperature limit. To attain this regime, it is often necessary to cool the system well below 1K. We put under scrutiny the magnitude of this term in different families of strongly-interacting electronic systems. For a wide range of compounds (including heavy-fermion, organic and various oxide families) a remarkable correlation between this term and the electronic specific heat is found. We argue that a dimensionless ratio relating these two signatures of mass renormalisation contains interesting information about the ground state of each system. The absolute value of this ratio remains close to unity in a wide range of strongly-correlated electron systems.
Valence Instability and Superconductivity in Heavy Fermion Systems
Alexander T. Holmes,Didier Jaccard,Kazumasa Miyake
Physics , 2006, DOI: 10.1143/JPSJ.76.051002
Abstract: Many cerium-based heavy fermion (HF) compounds have pressure-temperature phase diagrams in which a superconducting region extends far from a magnetic quantum critical point. In at least two compounds, CeCu2Si2 and CeCu2Ge2, an enhancement of the superconducting transition temperature was found to coincide with an abrupt valence change, with strong circumstantial evidence for pairing mediated by critical valence, or charge transfer, fluctuations. This pairing mechanism, and the valence instability, is a consequence of a f-c Coulomb repulsion term U_fc in the hamiltonian. While some non-superconducting Ce compounds show a clear first order valence instability, analogous to the Ce alpha-gamma transition, we argue that a weakly first order valence transition may be a general feature of Ce-based HF systems, and both magnetic and critical valence fluctuations may be responsible for the superconductivity in these systems.
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