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Papers by Alessio D'Alessandro

Research paper thumbnail of Electrically Small Matched Antennas With Time-Periodic and Space- Uniform Modulation

IEEE Transactions on Antennas and Propagation

A conceptual method to realize an impedancematched electrically small antenna is discussed, using... more A conceptual method to realize an impedancematched electrically small antenna is discussed, using a transmission line modulated only in time. The time-periodic spaceuniform modulation of a distributed shunt array of varcapacitors excites a mode with very small frequency but still a small (microwave) wavelength: the matching line then retains a practical size. The modulated transmission line brings the problem of impedance matching to a frequency f0 much higher than the signal, where the large antenna reactance can be easily compensated with a much higher bandwidth for the same Q factor: actually the bandwidth ∆f = f0/Q becomes large when f0 is much larger than the signal frequency. A simple way to obtain the space uniform modulation of the transmission line is illustrated, making use of a Wheatstone-bridge arrangement of the modulated varicaps. The signal and modulating lines, running in parallel on a section of the same length, see two very different equivalent shunt capacitances, so that the modulating voltage is almost uniform while the signal voltage may change significantly across the transmission line.

Research paper thumbnail of Physical understanding of an echo-Doppler test with voice-induced vibration

The physical understanding of a method of detecting mammalian cancer via vocalization during a no... more The physical understanding of a method of detecting mammalian cancer via vocalization during a normal echo-Doppler test is provided. The backscattered ultrasound frequency in the case of a vocal humming resonating in the chest wall is computed: the overall effect is that the signal/noise ratio could be easily improved at no cost. Clinical results are to appear separately elsewhere.

Research paper thumbnail of Confining properties of two-color QCD at finite density

Proceedings of The XXV International Symposium on Lattice Field Theory — PoS(LATTICE 2007), 2008

Research paper thumbnail of Magnetic Monopoles in the Deconfined Phase of Yang-Mills Theories

Proceedings of International Workshop on QCD Green’s Functions, Confinement and Phenomenology — PoS(QCD-TNT09), 2010

Research paper thumbnail of Magnetic monopoles in high temperature QCD

Proceedings of VIIIth Conference Quark Confinement and the Hadron Spectrum — PoS(ConfinementVIII), 2012

Research paper thumbnail of Confining properties in finite density QCD

AIP Conference Proceedings, 2007

We study the confining properties of two-color QCD at finite temperature and density by means of ... more We study the confining properties of two-color QCD at finite temperature and density by means of a disorder parameter detecting dual superconductivity of the QCD vacuum. We show that the disappearance of dual superconductivity (deconfinement) can be induced by a finite density of baryonic matter and that this phenomenon coincides with the restoration of chiral symmetry both at zero and

Research paper thumbnail of Dual superconductivity and typology of the QCD vacuum

AIP Conference Proceedings, 2007

According to this model the QCD vacuum behaves like a dual superconductor, "dual" as the roles of... more According to this model the QCD vacuum behaves like a dual superconductor, "dual" as the roles of the electric and magnetic fields are exchanged: the (chromo)electric field between two static color charges is compelled in narrow flux tubes yielding a linearly rising potential and confinement. Magnetic monopoles in the dual picture are the analogue of Cooper pairs in a superconductor: in the confined phase they condense breaking the U (1) electromagnetic symmetry.

Research paper thumbnail of Confining properties of 2-color QCD at finite density

We study the confining properties of QCD with two colors across the finite density phase transiti... more We study the confining properties of QCD with two colors across the finite density phase transition. A disorder parameter detecting dual superconductivity of the QCD vacuum is used as a probe for the confinement/deconfinement phase transition.

Research paper thumbnail of Confining properties of QCD at finite temperature and density

Physical Review D, 2007

A disorder parameter detecting dual superconductivty of the vacuum is used as a probe to characte... more A disorder parameter detecting dual superconductivty of the vacuum is used as a probe to characterize the confining properties of the phase diagram of two color QCD at finite temperature and density. We obtain evidence for the disappearing of dual superconductivity (deconfinement) induced by a finite density of baryonic matter, as well as for a coincidence of this phenomenon with the restoration of chiral symmetry both at zero and finite density. The saturation transition induced by Pauli blocking is studied as well, and a general warning is given about the possible effects that this unphysical transition could have on the study of the QCD phase diagram at strong values of the gauge coupling.

Research paper thumbnail of Thermal monopole condensation and confinement in finite temperature Yang-Mills theories

Physical Review D, 2010

We investigate the connection between Color Confinement and thermal Abelian monopoles populating ... more We investigate the connection between Color Confinement and thermal Abelian monopoles populating the deconfined phase of SU(2) Yang-Mills theory, by studying how the statistical properties of the monopole ensemble change as the confinement/deconfinement temperature is approached from above. In particular we study the distribution of monopole currents with multiple wrappings in the Euclidean time direction, corresponding to two or more particle permutations, and show that multiple wrappings increase as the deconfinement temperature is approached from above, in a way compatible with a condensation of such objects happening right at the deconfining transition. We also address the question of the thermal monopole mass, showing that different definitions give consistent results only around the transition, where the monopole mass goes down and becomes of the order of the critical temperature itself.

Research paper thumbnail of Magnetic monopoles in the high temperature phase of Yang–Mills theories

Nuclear Physics B, 2008

We investigate the properties of thermal abelian magnetic monopoles in the high temperature phase... more We investigate the properties of thermal abelian magnetic monopoles in the high temperature phase of Yang-Mills theories, following a recent proposal for their identification on lattice configurations. The study is done for SU(2) pure gauge theory, for temperatures going up to about 10 times the deconfining temperature and using the Maximal Abelian gauge to perform the abelian projection. We find that the monopole density has a well defined continuum limit. Its temperature dependence disagrees with a free particle gas prediction and is instead well described by a T 3 /(log(T /Λ)) α behaviour in all the explored range, with α ∼ 2 and Λ ∼ 100 MeV. Also the study of spatial correlations of thermal monopoles shows the presence of non-trivial interactions among them. Finally, we discuss the gauge dependence of our results, showing that it is significant and that, even within the Maximal Abelian gauge, Gribov copy effects are important.

Research paper thumbnail of Electrically Small Matched Antennas With Time-Periodic and Space- Uniform Modulation

IEEE Transactions on Antennas and Propagation

A conceptual method to realize an impedancematched electrically small antenna is discussed, using... more A conceptual method to realize an impedancematched electrically small antenna is discussed, using a transmission line modulated only in time. The time-periodic spaceuniform modulation of a distributed shunt array of varcapacitors excites a mode with very small frequency but still a small (microwave) wavelength: the matching line then retains a practical size. The modulated transmission line brings the problem of impedance matching to a frequency f0 much higher than the signal, where the large antenna reactance can be easily compensated with a much higher bandwidth for the same Q factor: actually the bandwidth ∆f = f0/Q becomes large when f0 is much larger than the signal frequency. A simple way to obtain the space uniform modulation of the transmission line is illustrated, making use of a Wheatstone-bridge arrangement of the modulated varicaps. The signal and modulating lines, running in parallel on a section of the same length, see two very different equivalent shunt capacitances, so that the modulating voltage is almost uniform while the signal voltage may change significantly across the transmission line.

Research paper thumbnail of Physical understanding of an echo-Doppler test with voice-induced vibration

The physical understanding of a method of detecting mammalian cancer via vocalization during a no... more The physical understanding of a method of detecting mammalian cancer via vocalization during a normal echo-Doppler test is provided. The backscattered ultrasound frequency in the case of a vocal humming resonating in the chest wall is computed: the overall effect is that the signal/noise ratio could be easily improved at no cost. Clinical results are to appear separately elsewhere.

Research paper thumbnail of Confining properties of two-color QCD at finite density

Proceedings of The XXV International Symposium on Lattice Field Theory — PoS(LATTICE 2007), 2008

Research paper thumbnail of Magnetic Monopoles in the Deconfined Phase of Yang-Mills Theories

Proceedings of International Workshop on QCD Green’s Functions, Confinement and Phenomenology — PoS(QCD-TNT09), 2010

Research paper thumbnail of Magnetic monopoles in high temperature QCD

Proceedings of VIIIth Conference Quark Confinement and the Hadron Spectrum — PoS(ConfinementVIII), 2012

Research paper thumbnail of Confining properties in finite density QCD

AIP Conference Proceedings, 2007

We study the confining properties of two-color QCD at finite temperature and density by means of ... more We study the confining properties of two-color QCD at finite temperature and density by means of a disorder parameter detecting dual superconductivity of the QCD vacuum. We show that the disappearance of dual superconductivity (deconfinement) can be induced by a finite density of baryonic matter and that this phenomenon coincides with the restoration of chiral symmetry both at zero and

Research paper thumbnail of Dual superconductivity and typology of the QCD vacuum

AIP Conference Proceedings, 2007

According to this model the QCD vacuum behaves like a dual superconductor, "dual" as the roles of... more According to this model the QCD vacuum behaves like a dual superconductor, "dual" as the roles of the electric and magnetic fields are exchanged: the (chromo)electric field between two static color charges is compelled in narrow flux tubes yielding a linearly rising potential and confinement. Magnetic monopoles in the dual picture are the analogue of Cooper pairs in a superconductor: in the confined phase they condense breaking the U (1) electromagnetic symmetry.

Research paper thumbnail of Confining properties of 2-color QCD at finite density

We study the confining properties of QCD with two colors across the finite density phase transiti... more We study the confining properties of QCD with two colors across the finite density phase transition. A disorder parameter detecting dual superconductivity of the QCD vacuum is used as a probe for the confinement/deconfinement phase transition.

Research paper thumbnail of Confining properties of QCD at finite temperature and density

Physical Review D, 2007

A disorder parameter detecting dual superconductivty of the vacuum is used as a probe to characte... more A disorder parameter detecting dual superconductivty of the vacuum is used as a probe to characterize the confining properties of the phase diagram of two color QCD at finite temperature and density. We obtain evidence for the disappearing of dual superconductivity (deconfinement) induced by a finite density of baryonic matter, as well as for a coincidence of this phenomenon with the restoration of chiral symmetry both at zero and finite density. The saturation transition induced by Pauli blocking is studied as well, and a general warning is given about the possible effects that this unphysical transition could have on the study of the QCD phase diagram at strong values of the gauge coupling.

Research paper thumbnail of Thermal monopole condensation and confinement in finite temperature Yang-Mills theories

Physical Review D, 2010

We investigate the connection between Color Confinement and thermal Abelian monopoles populating ... more We investigate the connection between Color Confinement and thermal Abelian monopoles populating the deconfined phase of SU(2) Yang-Mills theory, by studying how the statistical properties of the monopole ensemble change as the confinement/deconfinement temperature is approached from above. In particular we study the distribution of monopole currents with multiple wrappings in the Euclidean time direction, corresponding to two or more particle permutations, and show that multiple wrappings increase as the deconfinement temperature is approached from above, in a way compatible with a condensation of such objects happening right at the deconfining transition. We also address the question of the thermal monopole mass, showing that different definitions give consistent results only around the transition, where the monopole mass goes down and becomes of the order of the critical temperature itself.

Research paper thumbnail of Magnetic monopoles in the high temperature phase of Yang–Mills theories

Nuclear Physics B, 2008

We investigate the properties of thermal abelian magnetic monopoles in the high temperature phase... more We investigate the properties of thermal abelian magnetic monopoles in the high temperature phase of Yang-Mills theories, following a recent proposal for their identification on lattice configurations. The study is done for SU(2) pure gauge theory, for temperatures going up to about 10 times the deconfining temperature and using the Maximal Abelian gauge to perform the abelian projection. We find that the monopole density has a well defined continuum limit. Its temperature dependence disagrees with a free particle gas prediction and is instead well described by a T 3 /(log(T /Λ)) α behaviour in all the explored range, with α ∼ 2 and Λ ∼ 100 MeV. Also the study of spatial correlations of thermal monopoles shows the presence of non-trivial interactions among them. Finally, we discuss the gauge dependence of our results, showing that it is significant and that, even within the Maximal Abelian gauge, Gribov copy effects are important.