365 research outputs found
Stereological analysis of hippocampus in rat treated with chemotherapeutic agent oxaliplatin
Background: Oxaliplatin (OX) has been widely used for treatment of colorectal and other cancers. Adverse effect of OX and other anticancer agents on cognition have been reported, but studies on the effects of chemotherapy on brain structure are scarce. This study describes the morphometrical features of the hippocampus structures in rat following OX treatment using design-based stereological methods.
Materials and methods: Ten male Wistar rats were randomised into two groups. The rats from OX group received 2.4 mg/kg OX in vehicle for 5 consecutive days every week for 2 weeks intraperitoneally. Controls received vehicle only. Cavalieri’s method and the optical fractionator method were used for volume and neuron estimation, respectively.
Results: Cavalieri’s method was used to estimate volume and showed that the volume of the hippocampus was significantly decreased in OX group (31.84 ± ± 1.24 mm3) compared with the vehicle control group (36.95 ± 3.48 mm3). The optical fractionator method was used to estimate neuron number and showed that the number of neurons in dentate gyrus, cornu ammonis 1 and 3 in OX group (8.147 ± 2.84 × 105, 4.257 ± 0.59 × 105 and 2.133 ± 0.22 × 105, respectively) did not differ from those of vehicle control group (7.36 ± 1.42 × 105, 3.521 ± ± 0.54 × 105 and 1.989 ± 0.46 × 105, respectively).
Conclusions: These findings suggested that OX treatment induces loss of hippocampal volume without neuronal loss which might help to clarify the mechanism by which OX affects cognition and to improve preventive treatment strategies
Photon position measure
The positive operator valued measure (POVM) for a photon counting array
detector is derived and found to equal photon flux density integrated over
pixel area and measurement time. Since photon flux density equals number
density multiplied by the speed of light, this justifies theoretically the
observation that a photon counting array provides a coarse grained measurement
of photon position. The POVM obtained here can be written as a set of
projectors onto a basis of localized states, consistent with the description of
photon position in a recent quantum imaging proposal [M. Tsang, Phys. Rev.
Lett. \textbf{102}, 253601 (2009)]. The wave function that describes a photon
counting experiment is the projection of the photon state vector onto this
localized basis. Collapse is to the electromagnetic vacuum and not to a
localized state, thus violating the text book rules of quantum mechanics but
compatible with the theory of generalized observables and the nonlocalizability
of an incoming photon
Spectrum generating algebra for the continuous spectrum of a free particle in Lobachevski space
In this paper, we construct a Spectrum Generating Algebra (SGA) for a quantum
system with purely continuous spectrum: the quantum free particle in a
Lobachevski space with constant negative curvature. The SGA contains the
geometrical symmetry algebra of the system plus a subalgebra of operators that
give the spectrum of the system and connects the eigenfunctions of the
Hamiltonian among themselves. In our case, the geometrical symmetry algebra is
and the SGA is . We start with a
representation of by functions on a realization of the
Lobachevski space given by a two sheeted hyperboloid, where the Lie algebra
commutators are the usual Poisson-Dirac brackets. Then, introduce a quantized
version of the representation in which functions are replaced by operators on a
Hilbert space and Poisson-Dirac brackets by commutators. Eigenfunctions of the
Hamiltonian are given and "naive" ladder operators are identified. The
previously defined "naive" ladder operators shift the eigenvalues by a complex
number so that an alternative approach is necessary. This is obtained by a non
self-adjoint function of a linear combination of the ladder operators which
gives the correct relation among the eigenfunctions of the Hamiltonian. We give
an eigenfunction expansion of functions over the upper sheet of two sheeted
hyperboloid in terms of the eigenfunctions of the Hamiltonian.Comment: 23 page
The various power decays of the survival probability at long times for free quantum particle
The long time behaviour of the survival probability of initial state and its
dependence on the initial states are considered, for the one dimensional free
quantum particle. We derive the asymptotic expansion of the time evolution
operator at long times, in terms of the integral operators. This enables us to
obtain the asymptotic formula for the survival probability of the initial state
, which is assumed to decrease sufficiently rapidly at large .
We then show that the behaviour of the survival probability at long times is
determined by that of the initial state at zero momentum . Indeed,
it is proved that the survival probability can exhibit the various power-decays
like for an arbitrary non-negative integers as ,
corresponding to the initial states with the condition as .Comment: 15 pages, to appear in J. Phys.
Secondary literacy across the curriculum: Challenges and possibilities
This paper discusses the challenges and possibilities attendant upon successfully implementing literacy across the curriculum initiatives – or ‘school language policies’ as they have come to be known - particularly at the secondary or high school level. It provides a theoretical background to these issues, exploring previous academic discussions of school language policies, and highlights key areas of concern as well as opportunity with respect to school implementation of such policies. As such, it provides a necessary conceptual background to the subsequent papers in this special issue, which focus upon the Secondary Schools’ Literacy Initiative (SSLI) – a New Zealand funded programme that aims to establish cross-curricular language and literacy policies in secondary schools
The Role of Additive Neurogenesis and Synaptic Plasticity in a Hippocampal Memory Model with Grid-Cell Like Input
Recently, we presented a study of adult neurogenesis in a simplified hippocampal memory model. The network was required to encode and decode memory patterns despite changing input statistics. We showed that additive neurogenesis was a more effective adaptation strategy compared to neuronal turnover and conventional synaptic plasticity as it allowed the network to respond to changes in the input statistics while preserving representations of earlier environments. Here we extend our model to include realistic, spatially driven input firing patterns in the form of grid cells in the entorhinal cortex. We compare network performance across a sequence of spatial environments using three distinct adaptation strategies: conventional synaptic plasticity, where the network is of fixed size but the connectivity is plastic; neuronal turnover, where the network is of fixed size but units in the network may die and be replaced; and additive neurogenesis, where the network starts out with fewer initial units but grows over time. We confirm that additive neurogenesis is a superior adaptation strategy when using realistic, spatially structured input patterns. We then show that a more biologically plausible neurogenesis rule that incorporates cell death and enhanced plasticity of new granule cells has an overall performance significantly better than any one of the three individual strategies operating alone. This adaptation rule can be tailored to maximise performance of the network when operating as either a short- or long-term memory store. We also examine the time course of adult neurogenesis over the lifetime of an animal raised under different hypothetical rearing conditions. These growth profiles have several distinct features that form a theoretical prediction that could be tested experimentally. Finally, we show that place cells can emerge and refine in a realistic manner in our model as a direct result of the sparsification performed by the dentate gyrus layer
Schrödinger operators with δ and δ′-potentials supported on hypersurfaces
Self-adjoint Schrödinger operators with δ and δ′-potentials supported on a smooth compact hypersurface are defined explicitly via boundary conditions. The spectral properties of these operators are investigated, regularity results on the functions in their domains are obtained, and analogues of the Birman–Schwinger principle and a variant of Krein’s formula are shown. Furthermore, Schatten–von Neumann type estimates for the differences of the powers of the resolvents of the Schrödinger operators with δ and δ′-potentials, and the Schrödinger operator without a singular interaction are proved. An immediate consequence of these estimates is the existence and completeness of the wave operators of the corresponding scattering systems, as well as the unitary equivalence of the absolutely continuous parts of the singularly perturbed and unperturbed Schrödinger operators. In the proofs of our main theorems we make use of abstract methods from extension theory of symmetric operators, some algebraic considerations and results on elliptic regularity
- …