University of Crete

About: University of Crete is a education organization based out in Rethymno, Greece. It is known for research contribution in the topics: Population & Galaxy. The organization has 8681 authors who have published 21684 publications receiving 709078 citations. The organization is also known as: Panepistimio Kritis.

Femtosecond switching of magnetism via strongly correlated spin–charge quantum excitations

Abstract: Magnetic order in a manganite can be switched during femtosecond photo-excitation via coherent superpositions of quantum states; this is analogous to processes in femtosecond chemistry where photoproducts of chemical and biochemical reactions can be influenced by creating suitable superpositions of molecular states. Today's magnetic memory and logic devices operate at gigahertz switching speeds. To achieve the even faster terahertz regime will require new technologies, and ultrafast all-optical magnetic switching using coherent spin manipulation is a leading contender. Ilias Perakis and colleagues demonstrate a development of this technique that achieves femtosecond all-optical switching of the magnetic state through the establishment of a 'colossal' magnetization component from an antiferromagnetic ground state. The switch to ferromagnetic ordering in Pr0.7Ca0.3MnO3 occurs within a mere 120 femtoseconds, a remarkably short time interval for a non-equilibrium magnetic phase transition. This is a new principle in magnetic switching, analogous to processes in femtochemistryin which photoproducts of chemical and biochemical reactions can be influenced by creating suitable superpositions of molecular states. This work is also of relevance to the fields of spin-chemistry, quantum biology and spin-electronics. The technological demand to push the gigahertz (109 hertz) switching speed limit of today’s magnetic memory and logic devices into the terahertz (1012 hertz) regime underlies the entire field of spin-electronics and integrated multi-functional devices. This challenge is met by all-optical magnetic switching based on coherent spin manipulation1. By analogy to femtosecond chemistry and photosynthetic dynamics2—in which photoproducts of chemical and biochemical reactions can be influenced by creating suitable superpositions of molecular states—femtosecond-laser-excited coherence between electronic states can switch magnetic order by ‘suddenly’ breaking the delicate balance between competing phases of correlated materials: for example, manganites exhibiting colossal magneto-resistance suitable for applications3,4. Here we show femtosecond (10−15 seconds) photo-induced switching from antiferromagnetic to ferromagnetic ordering in Pr0.7Ca0.3MnO3, by observing the establishment (within about 120 femtoseconds) of a huge temperature-dependent magnetization with photo-excitation threshold behaviour absent in the optical reflectivity. The development of ferromagnetic correlations during the femtosecond laser pulse reveals an initial quantum coherent regime of magnetism, distinguished from the picosecond (10−12 seconds) lattice-heating regime characterized by phase separation without threshold behaviour5,6. Our simulations reproduce the nonlinear femtosecond spin generation and underpin fast quantum spin-flip fluctuations correlated with coherent superpositions of electronic states to initiate local ferromagnetic correlations. These results merge two fields, femtosecond magnetism in metals and band insulators1,7,8,9, and non-equilibrium phase transitions of strongly correlated electrons10,11,12,13,14,15,16,17, in which local interactions exceeding the kinetic energy produce a complex balance of competing orders.

Direct comparison of the rheology of model hard and soft particle glasses

Abstract: The effects of particle softness and the role of the outer shell mechanics on the linear viscoelasticity and yielding behaviour of colloidal glasses are critically assessed using three different model colloidal particles: (i) sterically stabilized PMMA particles with model hard sphere interactions, (ii) core–shell microgels with a deformable PNIPAM outer shell and (iii) ultra-soft star-like micelles with inter-penetrable multi-arms. The volume fraction dependence of the elastic modulus and the yield stress reflects the softness of the effective inter-particle potential. The yield strain exhibits distinct non-monotonic volume fraction dependence for hard spheres below close packing whereas for both soft particles it increases above close packing due to particle softness. Stress overshoots in start-up shear show a common increase with shear rate in all systems. However, the stress overshoots are significantly stronger in star-like micelles due to transient arm entanglements. In relation with that similar stress peaks are detected within the period of the large amplitude oscillatory shear only in star-like micelles. Finally, we discuss the scaling exponents for the G′ and G′′ decrease at large oscillatory strain amplitudes and their relation with steady shear stress.

Space telescope and optical reverberation mapping project. i. ultraviolet observations of the seyfert 1 galaxy ngc 5548 with the cosmic origins spectrograph on hubble space telescope

Abstract: We describe the first results from a six-month long reverberation-mapping experiment in the ultraviolet based on 171 observations of the Seyfert 1 galaxy NGC 5548 with the Cosmic Origins Spectrograph on the Hubble Space Telescope. Significant correlated variability is found in the continuum and broad emission lines, with amplitudes ranging from ∼30% to a factor of two in the emission lines and a factor of three in the continuum. The variations of all the strong emission lines lag behind those of the continuum, with He II λ1640 lagging behind the continuum by ∼2.5 days and Lyα λ1215 ,C IV λ1550, and Si IV λ1400 lagging by ∼5–6 days. The relationship between the continuum and emission lines is complex. In particular, during the second half of the campaign, all emission-line lags increased by a factor of 1.3–2 and differences appear in the detailed structure of the continuum and emissionline light curves. Velocity-resolved cross-correlation analysis shows coherent structure in lag versus line of sight velocity for the emission lines; the high-velocity wings of C IV respond to continuum variations more rapidly than the line core, probably indicating higher velocity broad-line region clouds at smaller distances from the central

Corticotropin-Releasing Hormone Augments Proinflammatory Cytokine Production from Macrophages In Vitro and in Lipopolysaccharide-Induced Endotoxin Shock in Mice

Abstract: Corticotropin-releasing hormone (CRH) exerts an anti-inflammatory effect indirectly, via cortisole production, and a proinflammatory effect directly on immune cells. The aim of the present work was to examine the effect of CRH on macrophage-derived cytokines both in vitro and in vivo. For the in vitro experiments we used two types of macrophages: (i) the RAW264.7 monocyte/macrophage cell line and (ii) thioglycolate-elicited peritoneal macrophages from BALB/c mice. We have found that CRH enhanced lipopolysaccharide (LPS)-induced tumor necrosis factor alpha (TNF-α), interleukin-1β (IL-1β), and IL-6 production. For the in vivo experiments we have used the LPS-induced endotoxin shock model in BALB/c mice, an established model for systemic inflammation in which macrophages are the major source of the proinflammatory cytokines responsible for the development of the shock. Administration of antalarmin, a synthetic CRH receptor 1 (CRHR1) antagonist, prior to LPS prolonged survival in a statistically significant manner. The effect was more evident at the early stages of endotoxin shock. CRHR1 blockade suppressed LPS-induced elevation of the macrophage-derived cytokines TNF-α, IL-1β, and IL-6, confirming the role of CRH signals in cytokine expression. In conclusion, our data suggest that CRH signals play an early and crucial role in augmenting LPS-induced proinflammatory cytokine production by macrophages. Our data suggest that the diffuse neuroendocrine system via CRH directly affects the immune system at the level of macrophage activation and cytokine production.