1,991 research outputs found
Root data with group actions
Suppose is a field, is a connected reductive algebraic -group,
is a maximal -torus in , and is a finite group that acts on
. From the above, one obtains a root datum on which
acts. Provided that preserves a positive
system in , not necessarily invariant under , we construct
an inverse to this process. That is, given a root datum on which
acts appropriately, we show how to construct a pair
, on which acts as above.
Although the pair and the action of are canonical only up to
an equivalence relation, we construct a particular pair for which is
-quasisplit and fixes a -stable pinning of .
Using these choices, we can define a notion of taking "-fixed points"
at the level of equivalence classes, and this process is compatible with a
general "restriction" process for root data with -action.Comment: v2: one word inserted, one citation inserted, one reference updated,
one misspelling correcte
Large entropy production inside black holes: a simple model
Particles dropped into a rotating black hole can collide near the inner
horizon with enormous energies. The entropy produced by these collisions can be
several times larger than the increase in the horizon entropy due to the
addition of the particles. In this paper entropy is produced by releasing large
numbers of neutrons near the outer horizon of a rotating black hole such that
they collide near the inner horizon at energies similar to those achieved at
the Relativistic Heavy Ion Collider. The increase in horizon entropy is
approximately 80 per dropped neutron pair, while the entropy produced in the
collisions is 160 per neutron pair. The collision entropy is produced inside
the horizon, so this excess entropy production does not violate Bousso's bound
limiting the entropy that can go through the black hole's horizon. The
generalized laws of black hole thermodynamics are obeyed. No individual
observer inside the black hole sees a violation of the second law of
thermodynamicsComment: 10 page
A 160-Gb/s OTDM demultiplexer based on parametric wavelength exchange
Parametric wavelength exchange (PWE) has been demonstrated as a versatile device in providing different functionalities. In this paper, we will concentrate, numerically and experimentally, on one of these functionalities, namely, all-optical time demultiplexing of 160-Gb/s return-to-zero (RZ) signals based on a pulsed-pump PWE in a 400 m highly nonlinear dispersion-shifted fiber. Experimental results show power penalties < 2.7 dB at bit-error rate of 10-9 for all demultiplexed 10-Gb/s RZ signals. We also derive theoretical expressions for the conversion/residual efficiencies and investigate the impact of pump pulse width and phase mismatch on these efficiencies. Furthermore, the impacts of pulsed-pump wavelength and power level on the characteristics of the switching window are investigated numerically. As a result, the demultiplexer can be easily upgraded to an add-drop multiplexer because of the complete exchange nature of PWE, which is justified by the surviving channels' waveform performance. © 2009 IEEE.published_or_final_versio
‘Like the stranger at a funeral who cries more than the bereaved’: ethical dilemmas in ethnographic research with children
This article contributes to debates on the practicality and utility of prior ethical review in ethnography and qualitative research using an ethnography of children’s involvement in artisanal gold mining work in Ghana as a case study. Reflecting on dilemmas and obstacles encountered in attempts to employ prescribed institutional ethical guidance modelled for childhood research in the UK during the fieldwork, the discussion brings to attention some of the problems that can arise when ethical guidance is not anchored in the lived realities or value systems of the setting in which fieldwork is conducted. The article seeks to rejuvenate calls for more flexible and socio-culturally responsive ethical review and practice as an alternative to the prescriptive ethical regimes
Improving compliance to colorectal cancer screening using blood and stool based tests in patients refusing screening colonoscopy in Germany
Background Despite strong recommendations for colorectal cancer (CRC)
screening, participation rates are low. Understanding factors that affect
screening choices is essential to developing future screening strategies.
Therefore, this study assessed patient willingness to use non-invasive stool
or blood based screening tests after refusing colonoscopy. Methods
Participants were recruited during regular consultations. Demographic, health,
psychological and socioeconomic factors were recorded. All subjects were
advised to undergo screening by colonoscopy. Subjects who refused colonoscopy
were offered a choice of non-invasive tests. Subjects who selected stool
testing received a collection kit and instructions; subjects who selected
plasma testing had a blood draw during the office visit. Stool samples were
tested with the Hb/Hp Complex Elisa test, and blood samples were tested with
the Epi proColon® 2.0 test. Patients who were positive for either were advised
to have a diagnostic colonoscopy. Results 63 of 172 subjects were compliant to
screening colonoscopy (37%). 106 of the 109 subjects who refused colonoscopy
accepted an alternative non-invasive method (97%). 90 selected the Septin9
blood test (83%), 16 selected a stool test (15%) and 3 refused any test (3%).
Reasons for blood test preference included convenience of an office draw,
overall convenience and less time consuming procedure. Conclusions 97% of
subjects refusing colonoscopy accepted a non-invasive screening test of which
83% chose the Septin9 blood test. The observation that participation can be
increased by offering non-invasive tests, and that a blood test is the
preferred option should be validated in a prospective trial in the screening
setting
True Neutrality as a New Type of Flavour
A classification of leptonic currents with respect to C-operation requires
the separation of elementary particles into the two classes of vector C-even
and axial-vector C-odd character. Their nature has been created so that to each
type of lepton corresponds a kind of neutrino. Such pairs are united in
families of a different C-parity. Unlike the neutrino of a vector type, any
C-noninvariant Dirac neutrino must have his Majorana neutrino. They constitute
the purely neutrino families. We discuss the nature of a corresponding
mechanism responsible for the availability in all types of axial-vector
particles of a kind of flavour which distinguishes each of them from others by
a true charge characterized by a quantum number conserved at the interactions
between the C-odd fermion and the field of emission of the corresponding types
of gauge bosons. This regularity expresses the unidenticality of truly neutral
neutrino and antineutrino, confirming that an internal symmetry of a
C-noninvariant particle is described by an axial-vector space. Thereby, a true
flavour together with the earlier known lepton flavour predicts the existence
of leptonic strings and their birth in single and double beta decays as a unity
of flavour and gauge symmetry laws. Such a unified principle explains the
availability of a flavour symmetrical mode of neutrino oscillations.Comment: 19 pages, LaTex, Published version in IJT
General Form of the Color Potential Produced by Color Charges of the Quark
Constant electric charge satisfies the continuity equation where is the current density of the electron.
However, the Yang-Mills color current density of the quark
satisfies the equation which is not a continuity
equation () which implies that a color charge
of the quark is not constant but it is time dependent where
are color indices. In this paper we derive general form of color
potential produced by color charges of the quark. We find that the general form
of the color potential produced by the color charges of the quark at rest is
given by \Phi^a(x) =A_0^a(t,{\bf x}) =\frac{q^b(t-\frac{r}{c})}{r}\[\frac{{\rm
exp}[g\int dr \frac{Q(t-\frac{r}{c})}{r}] -1}{g \int dr
\frac{Q(t-\frac{r}{c})}{r}}\]_{ab} where integration is an indefinite
integration, ~~ , ~~, ~~ is the retarded time, ~~ is the speed
of light, ~~ is the position of the quark at the retarded
time and the repeated color indices (=1,2,...8) are summed. For constant
color charge we reproduce the Coulomb-like potential
which is consistent with the Maxwell theory where
constant electric charge produces the Coulomb potential
.Comment: Final version, two more sections added, 45 pages latex, accepted for
publication in JHE
Messages from the other side: parasites receive damage cues from their host plants
As sessile organisms, plants rely on their environment for cues indicating imminent herbivory. These cues can originate from tissues on the same plant or from different individuals. Since parasitic plants form vascular connections with their host, parasites have the potential to receive cues from hosts that allow them to adjust defenses against future herbivory. However, the role of plant communication between hosts and parasites for herbivore defense remains poorly investigated. Here we examined the effects of damage to lupine hosts (Lupinus texensis) on responses of the attached hemiparasite (Castilleja indivisa), and indirectly, on a specialist herbivore of the parasite, buckeyes (Junonia coenia). Lupines produce alkaloids as defenses against herbivore that can be taken up by the parasite. We found that damage to lupine host plants by beet armyworm (Spodoptera exigua) significantly increased jasmonic acid (JA) levels in both the lupine host and parasite, suggesting uptake of phytohormones or priming of parasite defenses using host cues. However, lupine host damage did not induce changes in alkaloid levels in the hosts or parasites. Interestingly, the parasite had substantially higher concentrations of JA and alkaloids compared to lupine host plants. Buckeye herbivores consumed more parasite tissue when attached to damaged compared to undamaged hosts. We hypothesize that increased JA due to lupine host damage induced higher iridoid glycosides in the parasite, which are feeding stimulants for this specialist herbivore. Our results demonstrate that damage to hosts may affect both parasites and associated herbivores, indicating cascading effects of host damage on multiple trophic levels
Effects of quantum gravity on the inflationary parameters and thermodynamics of the early universe
The effects of generalized uncertainty principle (GUP) on the inflationary
dynamics and the thermodynamics of the early universe are studied. Using the
GUP approach, the tensorial and scalar density fluctuations in the inflation
era are evaluated and compared with the standard case. We find a good agreement
with the Wilkinson Microwave Anisotropy Probe data. Assuming that a quantum gas
of scalar particles is confined within a thin layer near the apparent horizon
of the Friedmann-Lemaitre-Robertson-Walker universe which satisfies the
boundary condition, the number and entropy densities and the free energy
arising form the quantum states are calculated using the GUP approach. A
qualitative estimation for effects of the quantum gravity on all these
thermodynamic quantities is introduced.Comment: 15 graghes, 7 figures with 17 eps graph
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