In recent years, gravitational models motivated by quantum corrections to gravity which introduce higher order terms like
R
2
or terms in which the Riemann tensor is not symmetric have been studied ...by several authors in the form of a general Brans-Dicke type model containing the Ricci scalar, the Holst term and the Nieh-Yan invariant. In this paper we focus on the less explored Jordan frame of such theories and in the comparison between both this frame and the Einstein one. Furthermore, we discuss the role of the transformation of the torsion under conformal transformations and show that the transformation proposed in this paper (extended conformal transformation) contains a special case of the projective transformation of the connection used in some of the papers that motivated this work. We discuss the role and advantages of the extended conformal transformation and show that this new approach can have interesting consequences by working with different variables such as the metric and torsion. Moreover, we study the stability of the system via a dynamical analysis in the Jordan frame, this in order to analyze whether or not we have the fixed points that can be later identified as the inflationary attractor and the unstable fixed point where inflation could take place. Finally we study the scale invariant case of the general model in the Jordan frame. We find out that both the scalar spectral index and the tensor-to-scalar ratio are in agreement with the latest Planck results.
This Letter presents a novel approach to realising and fabricating a planar balun structure, where conventional bond wires are replaced by conductor bridges supported on polyimide blocks. Three ...different prototype structures were fabricated on 10 mil thick alumina substrate (ɛr = 9.8, tan δ = 0.0001) using thin film fabrication technology. More than double octave bandwidths are reported, from 1.25 to 4.7 GHz with losses lower than 1 dB, an amplitude imbalance (trace separation) below 0.75 dB and phase imbalance within ±5°. Measurements show good agreement with simplified 2D EM simulations. The performance of the balun is assessed for suitability in applications where amplitude and phase balance are of critical importance, such as push–pull or outphasing amplifier topologies.
In this work we present the results of the experimental characterization of Silicon Drift Detectors (SDDs) readout by CUBE preamplifiers for X-ray spectroscopy measurements. One specific goal of the ...work was to characterize SDDs of different sizes cooled at low temperature in view of their use in the upgrade of the SIDDHARTA nuclear physics experiment. Beside the target application, the results of this work are also of interest for a more extended use of the SDDs in other X-ray spectroscopy applications. The SDDs have been designed as single units with square shape of different areas, 64 mm 2 (8 mm × 8 mm) and 144 mm 2 (12 mm × 12 mm), and also as monolithic array of 3×3 elements of the 8 mm × 8 mm unit (total area 26 mm × 26 mm). The read-out of the SDDs is based on a CMOS (Complementary Metal Oxide Semiconductor) preamplifier (CUBE) both for the single unit and for the 3×3 array. For the readout of the array, an Application Specific Integrated Circuit (ASIC) has been used. An energy resolution better than 124 eV at the Mn-Kα line has been measured with a 64 mm 2 SDD cooled at the temperature of 50 K. The energy resolution remains good (<;130 eV) also at short shaping time (250 ns) thanks to the noise feature of the CUBE preamplifier. Results of measurements on SDDs of different format and also on arrays of SDDs are presented in this work.
The relationships between phase distortion, bias point and load modulation in power amplifiers are experimentally evaluated for two different GaN HEMT technologies. Measurements on devices with fixed ...and modulated load, to emulate the dynamic working conditions of the main stage of a Doherty amplifier, have been carried out through an advanced source/load-pull setup. Almost flat phase distortion against output power can be obtained by the proper bias point when the load remains constant, whereas it is shown that this possibility is not compatible with load modulation, inherently present in Doherty power amplifiers.
A new multi-modality imaging tool is under development in the framework of the INSERT (INtegrated SPECT/MRI for Enhanced Stratification in Radio-chemo Therapy) project, supported by the European ...Community. The final goal is to develop a custom SPECT apparatus, that can be used as an insert for commercially available MRI systems such as 3T MRI with 59cm bore diameter. INSERT is expected to offer more effective and earlier diagnosis with potentially better outcome in survival for the treatment of brain tumors, primarily glioma. Two SPECT prototypes will be developed, one dedicated to preclinical imaging, the second one dedicated to clinical imaging.
The basic building block of the SPECT detector ring is a small 5cm×5cm gamma camera, based on the well-established Anger architecture with a continuous scintillator readout by an array of silicon photodetectors. Silicon Drift Detectors (SDDs) and Silicon PhotoMultipliers (SiPM) are being considered as possible scintillator readout, considering that the detector choice plays a predominant role for the final performance of the system, such as energy and spatial resolution, as well as the useful field of view of the camera. Both solutions are therefore under study to evaluate their performances in terms of field of view (FOV), spatial and energy resolution. Preliminary simulations for both the preclinical and clinical systems have been carried out to evaluate resolution and sensitivity.
•We introduce INSERT, a new multi-modality SPECT/MRI instrument.•We propose two possible photodetectors (SDD, SiPM) for the scintillators readout.•We show possible results for INSERT, based on simulations.
We study the excited states of the pairing Hamiltonian providing an expansion for their energy in the strong coupling limit. To assess the role of the pairing interaction we apply the formalism to ...the case of a heavy atomic nucleus. We show that only a few statistical moments of the level distribution are sufficient to yield an accurate estimate of the energy for not too small values of the coupling G and we give the analytic expressions of the first four terms of the series. Further, we discuss the convergence radius Gsing of the expansion showing that it strongly depends upon the details of the level distribution. Furthermore Gsing is not related to the critical values of the coupling Gcrit, which characterize the physics of the pairing Hamiltonian, since it can exist even in the absence of these critical points.
•We study the excitation spectrum of the pairing Hamiltonian.•We provide an analytic expansion around the strong coupling limit.•We discuss the convergence radius of the expansion.•We connect the radius with the critical points of H.
Isoscalar dipole strength distributions in spherical medium- and heavy-mass nuclei are calculated within random phase approximation (RPA) or quasiparticle RPA. Different Skyrme-type interactions ...corresponding to incompressibilities in the range 200–250 MeV are used. The results are discussed in comparison with existing data on isoscalar giant dipole resonances. Two main issues are raised, firstly the calculated giant resonance energies are somewhat higher than the observed ones, and secondly a sizable fraction of strength is predicted below 20 MeV which needs to be experimentally confirmed.
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