Romanian Space Science Institute

Ilfov, Romania

Romanian Space Science Institute

Ilfov, Romania
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Paraipan M.,Romanian Space Science Institute
EPJ Web of Conferences | Year: 2017

The spatial distribution of neutron fluences in the extended uranium target ("Quinta" assembly) irradiated with 0.66 GeV proton, 4 AGeV deuteron and carbon beams was studied using the reactions with different threshold energy (Eth). The data sets were obtained with 59Co samples. The accumulation rates for the following isotopes: 60Co (Eth 0 MeV), 59Fe (Eth 3 MeV), 58Co (Eth 10 MeV), 57Co (Eth 20 MeV), 56Co (Eth 32 MeV), 47Sc (Eth 55 MeV), and 48V (Eth 70 MeV) were measured with HPGe spectrometer. The experimental accumulation rates were compared with the predictions of the simulations with Geant4 code. Substantial difference between the reconstructed and the simulated data for the hard part of the neutron spectrum was analyzed. © The Authors, published by EDP Sciences, 2017.

Casadio R.,University of Bologna | Casadio R.,National Institute of Nuclear Physics, Italy | Micu O.,Romanian Space Science Institute | Scardigli F.,Polytechnic of Milan | Scardigli F.,Kyoto University
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

We address the issue of (quantum) black hole formation by particle collision in quantum physics. We start by constructing the horizon wave-function for quantum mechanical states representing two highly boosted non-interacting particles that collide in flat one-dimensional space. From this wave-function, we then derive a probability that the system becomes a black hole as a function of the initial momenta and spatial separation between the particles. This probability allows us to extend the hoop conjecture to quantum mechanics and estimate corrections to its classical counterpart. © 2014 The Authors.

Baldea I.,University of Heidelberg | Baldea I.,Romanian Space Science Institute
Nanoscale | Year: 2013

Results of a seminal study (B. Xu and N. J. Tao, Science, 2003, 301, 1221) on the single-molecule junctions based on bipyridine placed in a solvent have been challenged recently (S. Y. Quek et al., Nat. Nano, 2009, 4, 230) by implicitly assuming a negligible solvent impact on the molecular transport and by merely considering low bias conductance data. In this paper we demonstrate that solvent effects on the molecular transport are important, and to show this we focus our attention on the energy offset ε0 of the dominant molecular orbital (LUMO) relative to the electrode Fermi level. To estimate the energy offset εsol0 from the full I-V curves presented by Xu and Tao for wet junctions, we resort to the recently proposed transition voltage spectroscopy (TVS). TVS, which plays a key role in the present analysis, emphasizes that data beyond the ohmic conductance regime are needed to reveal the solvent impact. We show that εsol0 significantly differs from the energy offset ε00 deduced for dry junctions (J. R. Widawsky et al., Nano Lett., 2012, 12, 354). The present work demonstrates that solvent effects on molecular transport are important and can be understood quantitatively. Results of ab initio calculations with and without solvent are reported that excellently explain the difference δε0 = εsol0 - ε00. δε0 = ΔΔG + δΦ + δW can be disentangled in contributions with a clear physical content: solvation energies (ΔΔG), image charges (δΦ), and work functions (δW). Accurate analytical formulae for ΔΔG and δΦ are reported, which provide experimentalists with a convenient framework to quantify solvent effects obviating demanding numerical efforts. © The Royal Society of Chemistry 2013.

Baildea I.,University of Heidelberg | Baildea I.,Romanian Space Science Institute
Journal of Physical Chemistry C | Year: 2013

In a recent experimental work, results of the first transition voltage spectroscopy (TVS) investigation on azurin have been reported. This forms a great case to better understand the electron transfer through bacterial redox metalloproteins, a process of fundamental importance from chemical, physical, and biological perspectives, and of practical importance for nano(bio)electronics. In the present paper we challenge the tentative interpretation put forward in the aforementioned experimental study and propose a different theoretical interpretation. To explain the experimental TVS data, we adopt an extended Newns-Anderson framework, whose accuracy and robustness is demonstrated. We show that that this framework clearly meets the need to obtain a consistent description across experiments. Most importantly, the presently proposed theoretical approach permits unraveling novel aspects on the impact of the electrochemical scanning microscope environment on the charge transport through single-(bio)molecule junctions based on redox units. The usefulness of TVS as a versatile method of investigation, also able to provide important insight into the charge transport through metalloproteins, is emphasized. © 2013 American Chemical Society.

Baldea I.,University of Heidelberg | Baldea I.,Romanian Space Science Institute
Faraday Discussions | Year: 2014

The accurate determination of the lowest electron attachment (EA) and ionization (IP) energies for molecules embedded in molecular junctions is important for correctly estimating, for example, the magnitude of the currents (I) or the biases (V) where an I-V curve exhibits significant non-Ohmic behavior. Benchmark calculations for the lowest electron attachment and ionization energies of several typical molecules utilized to fabricate single-molecule junctions characterized by n-type conduction (4,4′-bipyridine, 1,4-dicyanobenzene and 4,4′-dicyano-1,1′-biphenyl) and p-type conduction (benzenedithiol, biphenyldithiol, hexanemonothiol and hexanedithiol) based on the EOM-CCSD (equation-of-motion coupled-cluster singles and doubles) state-of-the-art method of quantum chemistry are presented. They indicate significant differences from the results obtained within current approaches to molecular transport. The present study emphasizes that, in addition to a reliable quantum chemical method, basis sets much better than the ubiquitous double-zeta set employed for transport calculations are needed. The latter is a particularly critical issue for correctly determining EAs, which is impossible without including sufficient diffuse basis functions. The spatial distribution of the dominant molecular orbitals (MOs) is another important issue, on which the present study draws attention, because it sensitively affects the MO energy shifts Φ due to image charges formed in electrodes. The present results cannot substantiate the common assumption of a point-like MO midway between electrodes, which substantially affects the actual Φ-values. © The Royal Society of Chemistry 2014.

Popa L.A.,Romanian Space Science Institute
Journal of Cosmology and Astroparticle Physics | Year: 2011

We consider the possibility to observationally differentiate the Standard Model (SM) Higgs driven inflation with non-minimal coupling to gravity from other variants of SM Higgs inflation based on the scalar field theories with non-canonical kinetic term such as Galileon-like kinetic term and kinetic term with non-minimal derivative coupling to the Einstein tensor. In order to ensure consistent results, we study the SM Higgs inflation variants by using the same method, computing the full dynamics of the background and perturbations of the Higgs field during inflation at quantum level. Assuming that all the SM Higgs inflation variants are consistent theories, we use the MCMC technique to derive constraints on the inflationary parameters and the Higgs boson mass from their fit to WMAP7+SN+BAO data set. We conclude that a combination of the SM Higgs mass measurement by the LHC and accurate determination by the PLANCK satellite of the spectral index of curvature perturbations and tensor-to-scalar ratio will enable to distinguish among these models. We also show that the consistency relations of the SM Higgs inflation variants are distinct enough to differentiate among them. © 2011 IOP Publishing Ltd and SISSA.

Popa V.,Romanian Space Science Institute
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2011

The aim of the KM3NeT Project is to build a very large volume (more than 1 km3) neutrino telescope in the Mediterranean Sea. The up to date status of the project is presented, and the main physics goals are reviewed. The possibility to search for super-massive exotic particles (magnetic monopoles, nuclearites, Q-balls) is addressed in the final part of the paper. © 2010 Elsevier B.V. All rights reserved.

Vatasescu M.,Romanian Space Science Institute
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2012

We consider a specific wave packet preparation arising from the control of tunneling in the 0g-(6s,6p3 /2) double well potential of a Cs 2 cold molecule with chirped laser pulses. Such a possibility to manipulate the population dynamics in the 0g-(6s,6p3 /2) potential appears in a pump-dump scheme designed to form cold molecules by photoassociation of two cold cesium atoms. The initial population in the 0g-(6s,6p3 /2) double well is a wave packet prepared in the outer well at large interatomic distances (94 a0) by a photoassociation step with a first chirped pulse, being a superposition of several vibrational states whose energies surround the energy of a tunneling resonance. Our present work is focused on a second delayed chirped pulse, coupling the 0g-(6s,6p3 /2) surface with the a3Σu+(6s,6s) one in the zone of the double well barrier (15 a0) and creating deeply bound cold molecules in the a3Σu+(6s,6s) state. We explore the parameters choice (intensity, duration, chirp rate and sign) for this second pulse, showing that picoseconds pulses with a negative chirp can lead to trapping of population in the inner well in strongly bound vibrational states, out of the resonant tunneling able to transfer it back to the outer well. © 2011 Elsevier B.V. All rights reserved.

Vatasescu M.,Romanian Space Science Institute
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We investigate the entanglement between electronic and vibrational degrees of freedom produced by a vibronic coupling in a molecular system described in the Born-Oppenheimer approximation. Entanglement in a pure state of the Hilbert space H=Hel Hvib is quantified using the von Neumann entropy of the reduced density matrix and the reduced linear entropy. Expressions for these entanglement measures are derived for the 2×Nv and 3×Nv cases of the bipartite entanglement, where 2 and 3 are the dimensions of the electronic Hilbert space Hel, and Nv is the dimension of Hvib. We study the entanglement dynamics for two electronic states coupled by a laser pulse (a 2×Nv case), taking as an example a coupling between the a3Σu+(6s,6s) and 1g(6s,6p3/2) states of the Cs2 molecule. The reduced linear entropy expression obtained for the 3×Nv case is used to follow the entanglement evolution in a scheme proposed for the control of the vibronic dynamics in a Cs2 cold molecule, implying the a3Σu+(6s,6s), 0g-(6s,6p3/2), and 0g-(6s,5d) electronic states, which are coupled by a nonadiabatic radial coupling and a sequence of chirped laser pulses. © 2013 American Physical Society.

Ghenescu V.,Romanian Space Science Institute
Nuclear and Particle Physics Proceedings | Year: 2016

The very forward region of the detector at a future linear collider will be instrumented with two sampling calorimeters - BeamCal and LumiCal - for fast beam parameter estimates, precise luminosity measurements, as well as for the improvement of the hermeticity of the detector at small angles. These very forward calorimeters are designed to sustain high radiation doses and deliver precise and valuable data for the machine- and physics-related measurements. Sensor and ASIC prototypes were developed and tested. Here we report on sensor characteristics and test-beam results obtained from a sensor plane assembled with front-end and ADC ASICs. © 2015 Elsevier B.V.

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