2,237 research outputs found
Brood cells like conifer cones: the peculiar nesting biology of the osmiine bee Hoplitis (Alcidamea) curvipes (Morawitz, 1871) (Hymenoptera, Megachilidae)
Two nests of Hoplitis curvipes are described from Apulia (Italy) and Dagestan (Russia). Both nests consisted of two brood cells placed side by side under a stone. The cells were neither attached to each other nor to the substrate. They were constructed from leaf fragments, which were imbricately arranged, forming a cone-like structure; each leaf fragment consisted of a basal part that was masticated to leaf pulp and an apical part that protruded freely from the cell wall. The cell wall was formed by the fusion of the masticated basal parts of the leaf fragments and thus entirely consisted of leaf pulp. The cell was sealed with a closing plug made of pure leaf pulp; a few leaf fragments were glued to its outer surface. The cocoon consisted of two layers: the outer layer was restricted to the anterior portion of the cell and had several longitudinal air-exchange slits on its lateral surface, while the inner layer had an air-exchange orifice in its most anterior dome-shaped top. Results of measurements of brood cell dimensions and contents are provided. The nesting biology of species of the H. curvipes group is discussed
Hadronic structure aspects of decays
As is known from previous studies the lepton number violating decays have good prospects to probe new physics beyond the
Standard Model and provide valuable information on neutrino masses and mixing.
We analyze these processes with an emphasis on their hadronic structure
aspects applying relativistic constituent quark model. We conclude that the
previously ignored contribution associated with the t-channel Majorana neutrino
exchange is comparable with the s-channel one in a wide range of neutrino
masses. We also estimated model independent absolute upper bounds on neutrino
contribution to these decays.Comment: 15 pages, 1 figure. Version to appear in PRD, normalization factor in
Eq. (25) is correcte
First-order multi-k phase transitions and magnetoelectric effects in multiferroic Co3TeO6
A theoretical description of the sequence of magnetic phases in Co3TeO6 is
presented. The strongly first-order character of the transition to the
commensurate multiferroic ground state, induced by coupled order parameters
corresponding to different wavevectors, is related to a large magnetoelastic
effect with an exchange energy critically sensitive to the interatomic spacing.
The monoclinic magnetic symmetry C2' of the multiferroic phase permits
spontaneous polarization and magnetization as well as the linear
magnetoelectric effect. The existence of weakly ferromagnetic domains is
verified experimentally by second harmonic generation measurements
Large temperature dependence of the Casimir force at the metal-insulator transition
The dependence of the Casimir force on material properties is important for
both future applications and to gain further insight on its fundamental
aspects. Here we derive a general theory of the Casimir force for
low-conducting compounds, or poor metals. For distances in the micrometer
range, a large variety of such materials is described by universal equations
containing a few parameters: the effective plasma frequency, dissipation rate
of the free carriers, and electric permittivity in the infrared range. This
theory can also describe inhomogeneous composite materials containing small
regions with different conductivity. The Casimir force for mechanical systems
involving samples made with compounds that have a metal-insulator transition
shows an abrupt large temperature dependence of the Casimir force within the
transition region, where metallic and dielectric phases coexist.Comment: 23 pages, 9 figure
Master Higher-Spin Particle
We propose a "master" higher-spin (HS) particle system. The particle model
relevant to the unfolded formulation of HS theory, as well as the HS particle
model with a bosonic counterpart of supersymmetry, follow from the master model
as its two different gauges. Quantization of the master system gives rise to a
new form of the massless HS equations in an extended space involving, besides
extra spinorial coordinates, also a complex scalar one. As solutions to these
equations we recover the massless HS multiplet with fields of all integer and
half-integer helicities, and obtain new multiplets with a non-zero minimal
helicity. The HS multiplets are described by complex wave functions which are
holomorphic in the scalar coordinate and carry an extra U(1) charge q. The
latter fully characterizes the given multiplet by fixing the minimal helicity
as q/2. We construct a twistorial formulation of the master system and present
the general solution of the associate HS equations through an unconstrained
twistor "prepotential".Comment: 21 pages, minor corrections, version to appear in Class. Quantum Gra
The results of U-Pb SHRIMP-II dating of zircon from granitoids of Talitsky molybdenum-bearing massif (eastern slope of the Middle Urals)
Age position and geodynamic conditions of molybdenum metallization and productive granitoids of the Urals formation are very little studied now. This publication contains the results of isotopic dating of granites from Talitsa Cu-Mo-porphyry deposit which should help solve this problem. The timing of formation of the molybdenum-bearing granitoids of Talitsa deposit was determined by applying the U-Pb SHRIMP-II method through zircons (the Center for Isotopic Research of All Russian Geological Research Institute, St.Petersburg). The U-Pb-age has been calculated on 7 (from a total of 11 conducted) measurements with probability of concordanсе 0.996 and MSWD = 0.105 and it is 297.4 ± 2.3 Ma. The results of U-Pb dating are similar to before published Re-Os ages of Talitsa molybdenite deposit: 299.9 ± ± 2.9 Ma and 298.3 ± 1.3 Ma. These data establishes the new unknown before age level of molybdenum metallization. Until recently there has been only data on the Yuzhno-Shameiskoe molybdenum deposit connected with the subalkaline granites of Malyshevo massif which is younger: 277.1 ± 1.1 Ma. According to the received data, the intrusion of investigated granitoids happened practically at the same time as the formation of the wide-spread in the western slope of the Middle Urals intrusive bodies which are accompanied by gold metallization (Verkhisetsky, Shartashsky and others). With such close (practically the same) time of formation the rocks of molybdenum-bearing and gold-bearing massifs significantly differ in petrochemical peculiarities, which probably determines their metallogenetic specialization. Granitoids forming gold-bearing quartz veins on chemical composition are rocks of calc-alkaline series (typical exemple - Shartashskyi massif with Beriozovsk gold deposite). The granitoids productive on of Cu-Mo-porphyry type metallization together with large number of normal alkalinity rocks includes subalkaline rocks such as monzodiorites and quartz monzodiorites
Galilean Conformal Mechanics from Nonlinear Realizations
We apply the nonlinear realizations method for constructing new Galilean
conformal mechanics models. Our starting point is the Galilean conformal
algebra which is a non-relativistic contraction of its relativistic
counterpart. We calculate Maurer-Cartan one-forms, examine various choices of
the relevant coset spaces and consider the geometric inverse Higgs-type
constraints which reduce the number of the independent coset parameters and, in
some cases, provide dynamical equations. New Galilean conformally invariant
actions are derived in arbitrary space-time dimension D=d+1 (no central
charges), as well as in the special dimension D=2+1 with one "exotic" central
charge. We obtain new classical mechanics models which extend the standard
(D=0+1) conformal mechanics in the presence of d non-vanishing space
dimensions.Comment: v2: 1 + 20 pages, small changes in Sect.5 and two references added;
the version will appear in Phys.Rev.
Geodynamic Significance of the Mesoproterozoic Magmatism of the Udzha Paleo-Rift (Northern Siberian Craton) Based on U-Pb Geochronology and Paleomagnetic Data
The emplacement age of the Great Udzha Dyke (northern Siberian Craton) was determined by the U-Pb dating of apatite using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). This produced an age of 1386 +/- 30 Ma. This dyke along with two other adjacent intrusions, which cross-cut the sedimentary units of the Udzha paleo-rift, were subjected to paleomagnetic investigation. The paleomagnetic poles for the Udzha paleo-rift intrusions are consistent with previous results published for the Chieress dyke in the Anabar shield of the Siberian Craton (1384 +/- 2 Ma). Our results suggest that there was a period of intense volcanism in the northern Siberian Craton, as well as allow us to reconstruct the apparent migration of the Siberian Craton during the Mesoproterozoic.Peer reviewe
Superconformal mechanics
We survey the salient features and problems of conformal and superconformal
mechanics and portray some of its developments over the past decade. Both
classical and quantum issues of single- and multiparticle systems are covered.Comment: 1+68 pages, invited review for Journal of Physics A; v2: revised text
extended by 4 pages and 11 references, published versio
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