לוח שנה משולב

The talk will explain various measurements of X-ray absorption of astrophysical sources and the immense challenge to physically characterize the intervening matter.
Only 10% of the baryons of the local Universe reside in galaxies, while 90% are conjectured to occupy the intergalactic medium in a form that makes it impossible to detect their electromagnetic emission.
It will be shown how recent measurements of photo-electric absorption of the farthest known X-ray point sources, namely gamma-ray bursts and quasars, can account for the long sought baryons.
Since X-ray absorption requires heavy elements (Z > 5), massive galactic winds are invoked to explain how these elements reached intergalactic space.
The utilization of high-resolution atomic spectroscopy for estimating the mass flow in galactic winds emanating from around supermassive black holes will be demonstrated.

The non-hermitian formalism of quantum mechanics enables one to solve problems which are extremely hard to solve and often even impossible to solve within the framework of the standard formalism of quantum mechanics.
It this talk I will focus on a situation where in non-hermitian quantum
mechanics two eigenvalues and their corresponding eigenfunctions are
degenerated eigenvalues and states, respectively. We will discuss the effect of
this "accidental" situation (which cannot happen in the standard formalism of
quantum mechanics) on different type of observable phenomena.

We will show how there are observable phenomena that can be predicted by the
non-hermiitian formalism of quantum mechanics in light matter interactions.
Either in propagation of light in waveguides or when atoms or molecules or
nanostructures interact with laser fields.

References to the CROSSING RULE in non-hermitian QM
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NM and S. Friedland, "The Association of Resonance States with the Incomplete
Spectrum of Finite Complex-Scaled Hamiltonian Matrices." Phys. Rev. A, 22,
618-623 (1980).

E. Narevicius and NM, "Fingerprints of broad overlapping resonances in the e+H2
cross section." Phys. Rev. Lett., 81, No. 11 (1998);

E. Narevicius and NM, "Trapping of an electron due to molecular vibrations."
Phys. Rev. Lett., 84, 1681 (2000).

E. Narevicius, P. Serra and NM, "Critical phenomena associated with
self-orthogonality in non_Hermitian quantum mechanics." Europhys. Lett., 62,
789-794 (2003).

S. Klaiman, U. Gunther, and NM, "Visualization of Branch Points in PT-Symmetric
Waveguides, Phys. Rev. Lett. 101, 080402 (2008)

O. Peleg, M. Segev, G. Bartal, D. N. Christodoulides, and NM, "NonlinearWaves
in SubwavelengthWaveguide Arrays: Evanescent Bands and the "Phoenix Soliton
Phys. Rev. Lett. 102, 163902 (2009).

O. Peleg, Y. Plotnik, NM, O. Cohen, and M. Segev, "Self-trapped leaky waves and
their interactions",
Phys. Rev A80, 041801(R) 2009.

R. Lefebvre, O. Atabek, M. Sindelka, and NM, "Resonance Coalescence in
Molecular Photodissociation", Phys. Rev. Lett. 103, 123003, (2009).

B. Alfassi, O. Peleg, NM, and M. Segev
"Diverging Rabi Oscillations in Subwavelength Photonic Lattices"
Phys. Rev. Lett. 106, 073901 (2011)

NM, "Non-Hermitian Quantum Mechanics", Cambridge University Press, 2011.

What are the sources of trial-to-trial variability in neural responses in early sensory cortical areas and how does this variability affect perceptual decisions? In this talk I will describe results from two studies that aim to address these questions. In the first study, we examined co-variations between behavioral choices of monkeys performing a threshold visual detection task and neural population responses recorded simultaneously from their V1. We found that fluctuations in V1 responses to the same visual stimulus are correlated with fluctuations in perceptual decisions. Our results provide insight regarding the decoding mechanisms that mediate behavior based on V1 responses and suggest that most choice-related variability is already present in V1. Top-down modulations from higher visual cortical areas are one potential source for these decision related signals in V1. The goal of the second study was to characterize two forms of top-down effects in V1: modulations by spatial uncertainty and by stimulus relevance. We found that V1 responses are unaffected by spatial uncertainty, suggesting that target sensitivity is not a limited resource that can be improved by focal attention in V1. Conversely, V1 responses were significantly modulated by stimulus relevance. These modulations are likely to contribute to spatial gating of task-irrelevant information. However, the spatial and temporal characteristics of this top-down signal suggest that it is not a major source of choice-related variability in V1. Our results are therefore consistent with a predominantly bottom-up source of decision related activity in V1.