3,783 research outputs found
The emergence of superconductivity in BaNi2(Ge1-xPx)2 at a structural instability
The physical properties and structural evolution of the 122-type solid
solution BaNi2(Ge1-xPx)2 are reported. The in-plane X-X (X = Ge1-xPx) dimer
formation present in the end member BaNi2Ge2, which results in a structural
transition to orthorhombic symmetry, is completely suppressed to zero
temperature on P substitution near x = 0.7, and a dome-shape superconducting
phase with a maximum Tc = 2.9 K emerges. Clear indications of phonon softening
and enhanced electron-phonon coupling are observed at the composition of the
structural instability. Our findings show that dimer breaking offers new
possibilities as a tuning parameter of superconductivity.Comment: 14 pages, 4 figure
Correlation potentials for molecular bond dissociation within the self-consistent random phase approximation
Self-consistent correlation potentials for H and LiH for various
inter-atomic separations are obtained within the random phase approximation
(RPA) of density functional theory. The RPA correlation potential shows a peak
at the bond midpoint, which is an exact feature of the true correlation
potential, but lacks another exact feature: the step important to preserve
integer charge on the atomic fragments in the dissociation limit. An analysis
of the RPA energy functional in terms of fractional charge is given which
confirms these observations. We find that the RPA misses the derivative
discontinuity at odd integer particle numbers but explicitly eliminates the
fractional spin error in the exact-exchange functional. The latter finding
explains the accurate total energy in the dissociation limit.Comment: 9 pages, 10 figure
Variability of aliphatic glucosinolates in Arabidopsis thaliana (L.) – Impact on glucosinolate profile and insect resistance
The glucosinolate(GS)-myrosinase system of Brassicaceae, including the model plant Arabidopsis thaliana (L.), comprises a defence which is effective especially against generalist herbivores. Based on their side chain structure GS are grouped into aliphatic, aromatic, and indolyl GS. Indolyl GS are widely distributed among A. thaliana ecotypes and the Brassicaceae family, but the presence of aliphatic GS is variable and under strong genetic control. We investigated the effect of AOP gene expression on the side chain modifications of GS and the impact on insect resistance. AOP2 and AOP3 genes from Mr-0 and Sap-0 ecotypes, respectively, were crossbred into the methylsulfinyl GS producing Gie-0. Successful crosses were heterozygote plants which produced allyl (AOP2) or 3-hydroxypropyl GS (AOP3). After self-pollination, the chemical profile of the F3 generation of plants was screened to identify homozygote lines. Homozygote lines producing 3-hydroxypropyl GS were compared to methylsulfinyl GS, which were used to study the impact of GS structure on insect performance in first experiments. Our experiments revealed that methylsulfinyl GS containing ecotype lines were more resistant to the generalist caterpillar Spodoptera exigua (Hübner) and to the specialist caterpillar Pieris brassicae (L.) than the lines containing hydroxypropyl GS as main compounds
Field-induced transition of the magnetic ground state from A-type antiferromagnetic to ferromagnetic order in CsCo2Se2
We report on the magnetic properties of CsCoSe with ThCrSi
structure, which we have characterized through a series of magnetization and
neutron diffraction measurements. We find that CsCoSe2 undergoes a
phase transition to an antiferromagnetically ordered state with a N\'eel
temperature of 66 K. The nearest neighbour interactions are
ferromagnetic as observed by the positive Curie-Weiss temperature of 51.0 K. We find that the magnetic structure of CsCoSe consists
of ferromagnetic sheets, which are stacked antiferromagnetically along the
tetragonal \textit{c}-axis, generally referred to as A-type antiferromagnetic
order. The observed magnitude of the ordered magnetic moment at = 1.5 K is
found to be only 0.20(1)/Co. Already in comparably small
magnetic fields of (5K) 0.3 T, we observe a
metamagnetic transition that can be attributed to spin-rearrangements of
CsCoSe, with the moments fully ferromagnetically saturated in a
magnetic field of (5K) 6.4 T. We discuss the entire
experimentally deduced magnetic phase diagram for CsCoSe with respect
to its unconventionally weak magnetic coupling. Our study characterizes
CsCoSe, which is chemically and electronically posed closely to the
superconductors, as a host of versatile magnetic
interactions
Probing the pairing symmetry in the over-doped Fe-based superconductor Ba_0.35Rb_0.65Fe_2As_2 as a function of hydrostatic pressure
We report muon spin rotation experiments on the magnetic penetration depth
lambda and the temperature dependence of lambda^{-2} in the over-doped Fe-based
high-temperature superconductor (Fe-HTS) Ba_{1-x}Rb_ xFe_2As_2 (x = 0.65)
studied at ambient and under hydrostatic pressures up to p = 2.3 GPa. We find
that in this system lambda^{-2}(T) is best described by d-wave scenario. This
is in contrast to the case of the optimally doped x = 0.35 system which is
known to be a nodeless s^{+-}-wave superconductor. This suggests that the
doping induces the change of the pairing symmetry from s^{+-} to d-wave in
Ba_{1-x}Rb_{x}Fe_{2}As_{2}. In addition, we find that the d-wave order
parameter is robust against pressure, suggesting that d is the common and
dominant pairing symmetry in over-doped Ba_{1-x}Rb_{x}Fe_{2}As_{2}. Application
of pressure of p = 2.3 GPa causes a decrease of lambda(0) by less than 5 %,
while at optimal doping x = 0.35 a significant decrease of lambda(0) was
reported. The superconducting transition temperature T_c as well as the gap to
T_c ratio 2Delta/k_BT_c show only a modest decrease with pressure. By combining
the present data with those previously obtained for optimally doped system x =
0.35 and for the end member x = 1 we conclude that the SC gap symmetry as well
as the pressure effects on the SC quantities strongly depend on the Rb doping
level. These results are discussed in the light of the putative Lifshitz
transition, i.e., a disappearance of the electron pockets in the Fermi surface
of Ba_{1-x}Rb_{x}Fe_{2}As_{2} upon hole doping.Comment: Accepted for publication in Physical Review
Evidence for strong lattice effects as revealed from huge unconventional oxygen isotope effects on the pseudogap temperature in LaSrCuO
The oxygen isotope (O/O) effect (OIE) on the pseudogap
(charge-stripe ordering) temperature is investigated for the cuprate
superconductor LaSrCuO as a function of doping by means
of x-ray absorption near edge structure (XANES) studies. A strong dependent
and sign reversed OIE on is observed. The OIE exponent
systematically decreases from for to for ,
corresponding to increasing and decreasing superconducting
transition temperature . Both and
exhibit a linear doping dependence with different
slopes and critical end points (where and
fall to zero) at and
, indicating a large positive OIE of
with an exponent of . The remarkably large and
strongly doping dependent OIE on signals a substantial involvement
of the lattice in the formation of the pseudogap, consistent with a polaronic
approach to cuprate superconductivity and the vibronic character of its ground
state
Paideia/Humanitas. I Classici per la Scuola dell'Europa. Venezia, Università Ca' Foscari, Auditorium Santa Margherita 26 febbraio 2010.
Cronaca del convegno
Potere e cultura in età augustea: Pordenone, Auditorium del Centro Studi 12 dicembre 2009.
Cronaca del convegno di Pordenone
'Femina lectissima'. Giulia, madre di Marco Antonio, tra descrizione e rappresentazione.
Il contributo ricostruisce il profilo biografico di Giulia, madre di Marco Antonio, e analizza la rappresentazione della matrona nella tradizione letteraria. Da un lato indaga come le particolari condizioni della tarda repubblica incisero nella promozione da parte di Giulia di iniziative innovative rispetto agli indirizzi del modello matronale e dall’altro lato studia come tali violazioni del mos maiorum furono valutate nella rappresentazione della madre di Marco Antonio da parte delle fonti coeve e posteriori. In questa prospettiva si analizzano le ragioni della legittimazione della matrona anche presso autori ostili a suo figlio e gli argomenti e le modalità della sua valorizzazione. The paper reconstructs the biography of Iulia, Mark Antony’s mother, and analyzes the representation of the matron in the literary tradition. Firstly, it investigates how the particular conditions of the late Republic influenced Iulia's realisation of innovative initiatives with respect to the feminine model and then studies how violations of the mos maiorum were evaluated in the representation of Mark Antony's mother by of the coeval and later sources. In this perspective the paper analyzes the reasons for the legitimacy of the matron even among authors who are hostile to her son and the issues and the methods of its valorization
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