The use of a broadband, frequency shaped femtosecond laser on translationally cold cesium molecules has recently demonstrated to be a very efficient method of cooling also the vibrational degree of freedom. A sample o...The use of a broadband, frequency shaped femtosecond laser on translationally cold cesium molecules has recently demonstrated to be a very efficient method of cooling also the vibrational degree of freedom. A sample of cold molecules, initially distributed over several vibrational levels, has thus been transfered into a single selected vibrational level of the singlet X^1∑g ground electronic state. Our method is based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but limited in its frequency bandwidth with a spatial light modulator. In such a way we are able to eliminate transitions from the selected level, in which molecules accumulate. In this paper we briefly report the main experimental results and then address, in a detailed way by computer simulations, the perspectives for a ＂complete＂ cooling of the molecules, including also the rotational degree of freedom. Since the pumping process strongly depends on the relative shape of the ground and excited potential curves, ro-vibrational cooling through different excited states is theoretically compared.展开更多
Amorphous alloys with a composition(at.%)Fe_(48)Cr_(15)Mo_(14)C_(15)B_(6)Y_(2) were prepared by using either pure elements(alloy B1)or a commercial AISI430 steel as a base material(B2).When prepared from pure elements...Amorphous alloys with a composition(at.%)Fe_(48)Cr_(15)Mo_(14)C_(15)B_(6)Y_(2) were prepared by using either pure elements(alloy B1)or a commercial AISI430 steel as a base material(B2).When prepared from pure elements,alloy(B1)could be cast in plate form with a fixed thickness of 2 mm and variable lengths between 10 and 20 mm by means of copper-mold injection in an air atmosphere.In the case of alloy B2,prepared by using commercial grade raw materials,rods of 2 mm diameter are obtained.Ribbons(B1 and B2)of width 5 mm and thickness about 30μm are prepared from the arc-melted ingots using a single roller melt spinner at a wheel speed of 40 m/s.The thermal and structural properties of the samples are measured by a combination of differential scanning calorimetry(DSC),x-ray diffraction and scanning electron microscopy.Chemical compositions are checked by energy dispersive spectroscopy analysis.X-ray diffraction and scanning electron microscopy observations confirm that an amorphous structure is obtained in all the samples.A minor fraction of crystalline phases(oxides and carbides)is detected on the as-cast surface.Values of hardness and Young modulus were measured by nanoindentation for both the alloys.The effects of adverse casting conditions(such as air atmosphere,non-conventional injection copper mold casting and the partial replacement of pure elements with commercial grade raw materials)on the glass formation and properties of the alloy are discussed.展开更多
The effects of rare earth addition on the glass forming ability of Fe50-xCr15Mo14C15B6Mx （x =0, 2 and M=Y, Gd） bulks and ribbons are studied. The thermal and structural properties of the samples are measured by a co...The effects of rare earth addition on the glass forming ability of Fe50-xCr15Mo14C15B6Mx （x =0, 2 and M=Y, Gd） bulks and ribbons are studied. The thermal and structural properties of the samples are measured by a combination of differential scanning calorimetry （DSC）, x-ray diffraction and scanning electron microscopy. Chemical compositions are checked by energy dispersive spectroscopy analysis. The copper mold casting technique leads to a fully amorphous structure up to 2mm only for compositions containing Y or Gd. In the case of ribbons, a fully amorphous phase is observed for all the compositions. The roles of Y and Gd are discussed on the basis of melting behavior analyzed by high-temperature DSC. Such elements act as oxygen scavengers, avoiding heterogeneous nucleation.展开更多
Fluctuations of energy and heat are investigated during the relaxation following the instantaneous temperature quench of an extended system. Results are obtained analytically for the Gaussian model and for the large N...Fluctuations of energy and heat are investigated during the relaxation following the instantaneous temperature quench of an extended system. Results are obtained analytically for the Gaussian model and for the large N model quenched below the critical temperature TC. The main finding is that fluctuations exceeding a critical threshold do condense. Though driven by a mechanism similar to that of Bose–Einstein condensation, this phenomenon is an out-of-equilibrium feature produced by the breaking of energy equipartition occurring in the transient regime. The dynamical nature of the transition is illustrated by phase diagrams extending in the time direction.展开更多
Cd1-xMnxTe/CdTe superlattices and thin films were grown by molecular beam epitaxy on GaAs （001） substrates. Spectroscopic ellipsometry measurements were performed on Cd1-x Mnx Te/ CdTe superlattices with composition...Cd1-xMnxTe/CdTe superlattices and thin films were grown by molecular beam epitaxy on GaAs （001） substrates. Spectroscopic ellipsometry measurements were performed on Cd1-x Mnx Te/ CdTe superlattices with compositions x = 0.4, 0.8, and Cd1-xMnx Te thin films with x = 0.2, 0.4, 0.6 at room temperature in the photon energy range 1.4-5 eV. In superlattices the pseudodielectric functions measured by ellipsometry show specific features related to the exciton transition between quantized interbands. The exciton transitions related to the heavy holes of 11 H, 22H, and 33H are observed and identified. In thin films spectroscopic ellipsometry allows the clear identification of the energy gap Eo. Additionally, critical point transitions are observable in both the spectra of the superlattices and films. Photoreflectance spectra were also performed at room temperature in order to compare with our ellipsometry results. After taking into account the strain-induced and quantum confinement effects, the theoretical calculations are in good agreement with our experimental spectra. Ellipsometry appears to be a suited technique to monitor the MBE growth, ultimately also in situ, of diluted magnetic low-dimensional systems.展开更多
In this paper we review some results obtained within the context of the predictive microbiology, which is a specific field of the population dynamics. In particular we discuss three models, which exploit tools of stat...In this paper we review some results obtained within the context of the predictive microbiology, which is a specific field of the population dynamics. In particular we discuss three models, which exploit tools of statistical mechanics, for bacterial dynamics in food of animal origin. In the first model, the random fluctuating behaviour, experimentally measured, of the temperature is considered. In the second model stochastic differential equations are introduced to take into account the influence of physical and chemical variables, such as temperature, pH and activity water, subject to deterministic and random variations. The third model, which is an extended version of the second one, neglects the environmental fluctuations, and concentrates on the role of the interspecific bacterial interactions. The comparison between expected results and observed data indicates that the presence of noise sources and interspecific bacterial interactions improves the predictive features of the models analyzed.展开更多
By analyzing phonon dispersion, we have evaluated the average Young＇s modulus and Poisson＇s ratio in graphite and in graphene grown on Ru（0001）, Pt（111）, Ir（111）, Ni（111）, and BC3/NbB2（0001）. In both flat ...By analyzing phonon dispersion, we have evaluated the average Young＇s modulus and Poisson＇s ratio in graphite and in graphene grown on Ru（0001）, Pt（111）, Ir（111）, Ni（111）, and BC3/NbB2（0001）. In both flat and corrugated graphene sheets and in graphite, we find a Poisson＇s ratio of 0.19 and a Young＇s modulus of 342 N/m. The unique exception is graphene/Ni（111）, for which we find different values because of the stretching of C-C bonds occurring in the commensurate overstructure （0.36 and 310 N/m for the Poisson＇s ratio and Young＇s modulus, respectively）. Such findings are in excellent agreement with calculations performed for a free-standing graphene membrane. The high crystalline quality of graphene grown on metal substrates leads to macroscopic samples with high tensile strength and bending flexibility for use in technological applications such as electromechanical devices and carbon-fiber reinforcements.展开更多
The typically tiny effect of radiation damping on a moving body can be amplified to a favorable extent by exploiting the sharp reflectivity slope at one edge of an optically induced stop-band in atoms loaded into an o...The typically tiny effect of radiation damping on a moving body can be amplified to a favorable extent by exploiting the sharp reflectivity slope at one edge of an optically induced stop-band in atoms loaded into an optical lattice.In this paper,this phenomenon is demonstrated for the periodically trapped and coherently driven cold 87Rb atoms,where radiation damping might be much larger than that anticipated in previous proposals and become comparable with radiation pressure.Such an enhancement could be observed even at speeds of only a few meters per second with less than 1.0%absorption,making radiation damping experimentally accessible.展开更多
We present an improved version of the superatom(SA)model to examine the slow-light dynamics of a few-photons signal field in cold Rydberg atoms with van der Waals(vdW)interactions.A main feature of this version is tha...We present an improved version of the superatom(SA)model to examine the slow-light dynamics of a few-photons signal field in cold Rydberg atoms with van der Waals(vdW)interactions.A main feature of this version is that it promises consistent estimations on total Rydberg excitations based on dynamic equations of SAs or atoms.We consider two specific cases in which the incident signal field contains more photons with a smaller detuning or less photons with a larger detuning so as to realize the single-photon-level light storage.It is found that vdW interactions play a significant role even for the slow-light dynamics of a single-photon signal field as distributed Rydberg excitations are inevitable in the picture of dark-state polariton.Moreover,the stored(retrieved)signal field exhibits a clearly asymmetric(more symmetric)profile because its leading and trailing edges undergo different(identical)traveling journeys,and higher storage/retrieval efficiencies with well preserved profiles apply only to weaker and well detuned signal fields.These findings are crucial to understand the nontrivial interplay of single-photon-level light storage and distributed Rydberg excitations.展开更多
文摘The use of a broadband, frequency shaped femtosecond laser on translationally cold cesium molecules has recently demonstrated to be a very efficient method of cooling also the vibrational degree of freedom. A sample of cold molecules, initially distributed over several vibrational levels, has thus been transfered into a single selected vibrational level of the singlet X^1∑g ground electronic state. Our method is based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but limited in its frequency bandwidth with a spatial light modulator. In such a way we are able to eliminate transitions from the selected level, in which molecules accumulate. In this paper we briefly report the main experimental results and then address, in a detailed way by computer simulations, the perspectives for a ＂complete＂ cooling of the molecules, including also the rotational degree of freedom. Since the pumping process strongly depends on the relative shape of the ground and excited potential curves, ro-vibrational cooling through different excited states is theoretically compared.
基金Supported by Regione Piemonte under Grant No D23the WWS Project of the Univerity of Torino.
文摘Amorphous alloys with a composition(at.%)Fe_(48)Cr_(15)Mo_(14)C_(15)B_(6)Y_(2) were prepared by using either pure elements(alloy B1)or a commercial AISI430 steel as a base material(B2).When prepared from pure elements,alloy(B1)could be cast in plate form with a fixed thickness of 2 mm and variable lengths between 10 and 20 mm by means of copper-mold injection in an air atmosphere.In the case of alloy B2,prepared by using commercial grade raw materials,rods of 2 mm diameter are obtained.Ribbons(B1 and B2)of width 5 mm and thickness about 30μm are prepared from the arc-melted ingots using a single roller melt spinner at a wheel speed of 40 m/s.The thermal and structural properties of the samples are measured by a combination of differential scanning calorimetry(DSC),x-ray diffraction and scanning electron microscopy.Chemical compositions are checked by energy dispersive spectroscopy analysis.X-ray diffraction and scanning electron microscopy observations confirm that an amorphous structure is obtained in all the samples.A minor fraction of crystalline phases(oxides and carbides)is detected on the as-cast surface.Values of hardness and Young modulus were measured by nanoindentation for both the alloys.The effects of adverse casting conditions(such as air atmosphere,non-conventional injection copper mold casting and the partial replacement of pure elements with commercial grade raw materials)on the glass formation and properties of the alloy are discussed.
文摘The effects of rare earth addition on the glass forming ability of Fe50-xCr15Mo14C15B6Mx （x =0, 2 and M=Y, Gd） bulks and ribbons are studied. The thermal and structural properties of the samples are measured by a combination of differential scanning calorimetry （DSC）, x-ray diffraction and scanning electron microscopy. Chemical compositions are checked by energy dispersive spectroscopy analysis. The copper mold casting technique leads to a fully amorphous structure up to 2mm only for compositions containing Y or Gd. In the case of ribbons, a fully amorphous phase is observed for all the compositions. The roles of Y and Gd are discussed on the basis of melting behavior analyzed by high-temperature DSC. Such elements act as oxygen scavengers, avoiding heterogeneous nucleation.
文摘Fluctuations of energy and heat are investigated during the relaxation following the instantaneous temperature quench of an extended system. Results are obtained analytically for the Gaussian model and for the large N model quenched below the critical temperature TC. The main finding is that fluctuations exceeding a critical threshold do condense. Though driven by a mechanism similar to that of Bose–Einstein condensation, this phenomenon is an out-of-equilibrium feature produced by the breaking of energy equipartition occurring in the transient regime. The dynamical nature of the transition is illustrated by phase diagrams extending in the time direction.
文摘Cd1-xMnxTe/CdTe superlattices and thin films were grown by molecular beam epitaxy on GaAs （001） substrates. Spectroscopic ellipsometry measurements were performed on Cd1-x Mnx Te/ CdTe superlattices with compositions x = 0.4, 0.8, and Cd1-xMnx Te thin films with x = 0.2, 0.4, 0.6 at room temperature in the photon energy range 1.4-5 eV. In superlattices the pseudodielectric functions measured by ellipsometry show specific features related to the exciton transition between quantized interbands. The exciton transitions related to the heavy holes of 11 H, 22H, and 33H are observed and identified. In thin films spectroscopic ellipsometry allows the clear identification of the energy gap Eo. Additionally, critical point transitions are observable in both the spectra of the superlattices and films. Photoreflectance spectra were also performed at room temperature in order to compare with our ellipsometry results. After taking into account the strain-induced and quantum confinement effects, the theoretical calculations are in good agreement with our experimental spectra. Ellipsometry appears to be a suited technique to monitor the MBE growth, ultimately also in situ, of diluted magnetic low-dimensional systems.
文摘In this paper we review some results obtained within the context of the predictive microbiology, which is a specific field of the population dynamics. In particular we discuss three models, which exploit tools of statistical mechanics, for bacterial dynamics in food of animal origin. In the first model, the random fluctuating behaviour, experimentally measured, of the temperature is considered. In the second model stochastic differential equations are introduced to take into account the influence of physical and chemical variables, such as temperature, pH and activity water, subject to deterministic and random variations. The third model, which is an extended version of the second one, neglects the environmental fluctuations, and concentrates on the role of the interspecific bacterial interactions. The comparison between expected results and observed data indicates that the presence of noise sources and interspecific bacterial interactions improves the predictive features of the models analyzed.
文摘By analyzing phonon dispersion, we have evaluated the average Young＇s modulus and Poisson＇s ratio in graphite and in graphene grown on Ru（0001）, Pt（111）, Ir（111）, Ni（111）, and BC3/NbB2（0001）. In both flat and corrugated graphene sheets and in graphite, we find a Poisson＇s ratio of 0.19 and a Young＇s modulus of 342 N/m. The unique exception is graphene/Ni（111）, for which we find different values because of the stretching of C-C bonds occurring in the commensurate overstructure （0.36 and 310 N/m for the Poisson＇s ratio and Young＇s modulus, respectively）. Such findings are in excellent agreement with calculations performed for a free-standing graphene membrane. The high crystalline quality of graphene grown on metal substrates leads to macroscopic samples with high tensile strength and bending flexibility for use in technological applications such as electromechanical devices and carbon-fiber reinforcements.
基金This work is supported by the National Natural Science Foundation of China(11104112)the National Basic Research Program of China(2011CB921603)the CRUI-British Council 2011 Exchange Program and the Fondo di Ateneo of the Brescia University
文摘The typically tiny effect of radiation damping on a moving body can be amplified to a favorable extent by exploiting the sharp reflectivity slope at one edge of an optically induced stop-band in atoms loaded into an optical lattice.In this paper,this phenomenon is demonstrated for the periodically trapped and coherently driven cold 87Rb atoms,where radiation damping might be much larger than that anticipated in previous proposals and become comparable with radiation pressure.Such an enhancement could be observed even at speeds of only a few meters per second with less than 1.0%absorption,making radiation damping experimentally accessible.
基金supported by the National Natural Science Foundation of China(Nos.11534002 and 12074061)the Cooperative Program by the Italian Ministry of Foreign Affairs and International Cooperation(No.PGR00960)the National Natural Science Foundation of China(No.11861131001).
文摘We present an improved version of the superatom(SA)model to examine the slow-light dynamics of a few-photons signal field in cold Rydberg atoms with van der Waals(vdW)interactions.A main feature of this version is that it promises consistent estimations on total Rydberg excitations based on dynamic equations of SAs or atoms.We consider two specific cases in which the incident signal field contains more photons with a smaller detuning or less photons with a larger detuning so as to realize the single-photon-level light storage.It is found that vdW interactions play a significant role even for the slow-light dynamics of a single-photon signal field as distributed Rydberg excitations are inevitable in the picture of dark-state polariton.Moreover,the stored(retrieved)signal field exhibits a clearly asymmetric(more symmetric)profile because its leading and trailing edges undergo different(identical)traveling journeys,and higher storage/retrieval efficiencies with well preserved profiles apply only to weaker and well detuned signal fields.These findings are crucial to understand the nontrivial interplay of single-photon-level light storage and distributed Rydberg excitations.
