22,223 research outputs found
Who Builds the Motherland?
I was born in 2002 into a middle-class Jewish family, in a very Jewish town. The town was our Zion, our Mini-Israel, our bubble. It prided itself on being a sleepy town where any American can feel safe and comfortable. At the best of times, the town felt like a family; everyone knew your name and many children born in the town decided to live the rest of their adult lives there. It was a place where the support of Israel was of utmost importance. Although everyone prided themselves on the security, there was always this unease that our human rights could be taken away by those others that outnumbered us. After all, it only took two years from Hitler\u27s rise to power to his passing of the Nuremberg laws. With this fear of history repeating itself, every Jew in the bubble, whether they be Reform or Orthodox, Ashkenazi or Sephardic, talked of the grandeur of the Israeli state. Because no matter how slim the odds may seem that the worst-case scenario could happen, any chance that it could happen again was unacceptable for the descendants of the victims of the Holocaust. [excerpt
Origin of spontaneous violation of the Lorentz symmetry: Vortices in the cosmos
By carefully studying the (1,0)+(0,1) representation space for massive
particles we point to the existence of certain inherent tachyonic dispersion
relations: E^2= p^2-m^2. We put forward an interpretation that exploits these
``negative mass squared'' solutions; rotational invariance is spontaneously
broken. Relevance of these results to the vortices in the cosmos is pointed
out.
NOTE: Just as "negative energy solutions'' of Dirac equation are
re-interpreted as antiparticles, similarly the possibility exists for
re-interpreting the tachyonic dispersion relations of all (j,0)+(0,j)
representation spaces via spontaneous Lorentz symmetry breaking. In Mod. Phys.
Lett. A8:2623-2630,1993 we exhibited this explicitly for the j=1 representation
space. The interest in this old subject has grown markedly in recent years as
is evident from numerous theoretical and phenomenological works on the subject.
With this observation, we make this replacement of our paper fourteen years
after its initial publication. The Abstract and main text remain unaltered. The
title is changed to reflect the underlying physics more closely.Comment: This is an exact copy of the published paper with an extended
bibliography and a revised title. A brief note is added to point out a
systematic way to spontaneously break Lorentz symmetr
Topological Phases for Fermionic Cold Atoms on the Lieb Lattice
We investigate the properties of the Lieb lattice, i.e a face-centered square
lattice, subjected to external gauge fields. We show that an Abelian gauge
field leads to a peculiar quantum Hall effect, which is a consequence of the
single Dirac cone and the flat band characterizing the energy spectrum. Then we
explore the effects of an intrinsic spin-orbit term - a non-Abelian gauge field
- and demonstrate the occurrence of the quantum spin Hall effect in this model.
Besides, we obtain the relativistic Hamiltonian describing the Lieb lattice at
low energy and derive the Landau levels in the presence of external Abelian and
non-Abelian gauge fields. Finally, we describe concrete schemes for realizing
these gauge fields with cold fermionic atoms trapped in an optical Lieb
lattice. In particular, we provide a very efficient method to reproduce the
intrinsic (Kane-Mele) spin-orbit term with assisted-tunneling schemes.
Consequently, our model could be implemented in order to produce a variety of
topological states with cold-atoms.Comment: 12 pages, 9 figure
The planetary nebula IC 5148 and its ionized halo
Many round or nearly roundish Planetary Nebulae (PNe) show multiple shells
and halo structures during their evolutionary stage near the maximum
temperature of their central star. Controversial debate is currently ongoing if
these structures are recombination halos, as suggested by hydrodynamic
modelling efforts, or ionized material. Recently we discovered a halo with even
somewhat unusual structures around the sparsely studied PN IC~5148 and present
for the first time spectroscopy going out to the halo of such a PN.} resolution
spectroscopy is used to derive dust chemistry and mineralogy. We investigate
the spatial distribution of material and its ionization state from the center
of the nebula up to the very outskirts of the halo. We obtained long-slit low
resolution spectroscopy (FORS2@VLT) of the nebula in two position angles, which
we used to investigate the nebular structure and its halo in the optical range
from 450 to 880\,nm. In addition we used medium resolution spectra taken with
X-SHOOTER@VLT ranging from 320 nm to 2.4 mu to derive atmospheric parameters
for the central star. We obtained the distance and position in the Galaxy from
various methods combined with GAIA DR2 data. We also applied Cloudy models to
the nebula in order to derive physical parameters of the various regions. We
obtained spatially resolved structures and detailed descriptions of the
outrunning shock front and a set of unusual halo structures denoted to further
shock. The halo structures appears clearly as hot ionized material. Furthermore
we derived a reliable photometric value for the central star at a GAIA distance
of D=1.3kpc. Considering the large distance \,kpc from the galactic
plane together to its non-circular motion in the galaxy and, a metallicity only
slightly below that of typical disk PNe, most likely IC 5148 originates from a
thick disk population star.Comment: 12 pages, 17 figures, accepted for publication in Astronomy &
Astrophysic
An integration scheme for reaction-diffusion models
A detailed description and validation of a recently developed integration
scheme is here reported for one- and two-dimensional reaction-diffusion models.
As paradigmatic examples of this class of partial differential equations the
complex Ginzburg-Landau and the Fitzhugh-Nagumo equations have been analyzed.
The novel algorithm has precision and stability comparable to those of
pseudo-spectral codes, but it is more convenient to employ for systems with
quite large linear extention . As for finite-difference methods, the
implementation of the present scheme requires only information about the local
enviroment and this allows to treat also system with very complicated boundary
conditions.Comment: 14 page, Latex - 4 EPS Figs - Submitted to Int. J. Mod. Phys.
Solar radio emission
Active areas of both observational and theoretical research in which rapid progress is being made are discussed. These include: (1) the dynamic spectrum or frequency versus time plot; (2) physical mechanisms in the development of various types of bursts; (3) microwave type 1, 2, 3, and moving type 4 bursts; (4) bursts caused by trapped electrons; (5) physics of type 3bursts; (6) the physics of type 2 bursts and their related shocks; (7) the physics of both stationary and moving traps and associated type 1 and moving type 4 bursts; and (8) the status of the field of solar radio emission
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