70 research outputs found
Boundary time crystals
This work was supported in part by \Progetti Interni - Scuola Normale Superiore" (A.R.), EU- 691 QUIC (R.F. and A.R.), CRF Singapore Ministry of Education (CPR-QSYNC 692) (R.F.), EPSRC program TOPNES (EP/I031014/1) (J.K.).In this work we introduce boundary time crystals. Here continuous time-translation symmetry breaking occurs only in a macroscopic fraction of a many-body quantum system. After introducing their definition and properties, we analyze in detail a solvable model where an accurate scaling analysis can be performed. The existence of the boundary time crystals is intimately connected to the emergence of a time-periodic steady state in the thermodynamic limit of a many-body open quantum system. We also discuss connections to quantum synchronization.PostprintPeer reviewe
Evidence of coexistence of change of caged dynamics at Tg and the dynamic transition at Td in solvated proteins
Mossbauer spectroscopy and neutron scattering measurements on proteins
embedded in solvents including water and aqueous mixtures have emphasized the
observation of the distinctive temperature dependence of the atomic mean square
displacements, , commonly referred to as the dynamic transition at some
temperature Td. At low temperatures, increases slowly, but it assume
stronger temperature dependence after crossing Td, which depends on the
time/frequency resolution of the spectrometer. Various authors have made
connection of the dynamics of solvated proteins including the dynamic
transition to that of glass-forming substances. Notwithstanding, no connection
is made to the similar change of temperature dependence of obtained by
quasielastic neutron scattering when crossing the glass transition temperature
Tg, generally observed in inorganic, organic and polymeric glass-formers.
Evidences are presented to show that such change of the temperature dependence
of from neutron scattering at Tg is present in hydrated or solvated
proteins, as well as in the solvents used unsurprisingly since the latter is
just another organic glass-formers. The obtained by neutron scattering at
not so low temperatures has contributions from the dissipation of molecules
while caged by the anharmonic intermolecular potential at times before
dissolution of cages by the onset of the Johari-Goldstein beta-relaxation. The
universal change of at Tg of glass-formers had been rationalized by
sensitivity to change in volume and entropy of the beta-relaxation, which is
passed onto the dissipation of the caged molecules and its contribution to
. The same rationalization applies to hydrated and solvated proteins for
the observed change of at Tg.Comment: 28 pages, 10 figures, 1 Tabl
Revealing the high-energy electronic excitations underlying the onset of high-temperature superconductivity in cuprates
In strongly-correlated systems the electronic properties at the Fermi energy (EF) are intertwined with those at high energy scales. One of the pivotal challenges in the field of high-temperature superconductivity (HTSC) is to understand whether and how the high energy scale physics associated with Mott-like excitations (|E-EF|>1 eV) is involved in the condensate formation. Here we show the interplay between the many-body high-energy CuO2 excitations at 1.5 and 2 eV and the onset of HTSC. This is revealed by a novel optical pump supercontinuum-probe technique, which provides access to the dynamics of the dielectric function in Y-Bi2212 over an extended energy range, after the photoinduced suppression of the superconducting pairing. These results unveil an unconventional mechanism at the base of HTSC both below and above the optimal hole concentration required to attain the maximum critical temperature (Tc)
Fast Scrambling at the Boundary
International audienceMany-body systems which saturate the quantum bound on chaos are attracting interest across a wide range of fields. Notable examples include the Sachdev-Ye-Kitaev model and its variations, all characterised by some form or randomness and all to all couplings. Here we study many-body quantum chaos in a quantum impurity model showing Non-Fermi-Liquid physics, the overscreened multichannel Kondo model. We compute exactly the low-temperature behavior of the out-of time order correlator in the limit of large and large number of channels , at fixed ratio . Due to strong correlations at the impurity site the spin fractionalizes in auxiliary fermions and bosons. We show that all the degrees of freedom of our theory acquire a Lyapunov exponent which is linear in temperature as , with a prefactor that depends on . Remarkably, for the impurity spin displays maximal chaos, while bosons and fermions only get up to half of the maximal Lyapunov exponent. Our results highlights two new features: a non-disordered model which is maximally chaotic due to strong correlations at its boundary and a fractionalization of quantum chaos
Boundary time crystals
In this work we introduce boundary time crystals. Here continuous time-translation symmetry breaking occurs only in a macroscopic fraction of a many-body quantum system. After introducing their definition and properties, we analyze in detail a solvable model where an accurate scaling analysis can be performed. The existence of the boundary time crystals is intimately connected to the emergence of a time-periodic steady state in the thermodynamic limit of a many-body open quantum system. We also discuss connections to quantum synchronization
Patellofemoral Joint Arthroplasty: Our Experience in Isolated Patellofemoral and Bicompartmental Arthritic Knees
Introduction Isolated patellofemoral (PF) arthritis is rare, and there is no complete agreement about the best surgical treatment. The operative treatments are total knee arthroplasty and patellofemoral replacement (PFR). The incidence of many early complications of PF arthroplasty has decreased with the introduction of newer designs. Nowadays, the main cause of revision surgery is the progression of tibiofemoral osteoarthritis. In the past, PF arthroplasty was contraindicated in patients with evidence of osteoarthritis or pain in medial or lateral tibiofemoral compartments. The improvement in implant designs and surgical techniques has allowed the addition of a monocompartmental arthroplasty for the medial or lateral tibiofemoral compartment. In this work, we evaluate our first experience with PF arthroplasty and its combination with unicompartmental knee arthroplasty. Materials and Methods From May 2014 to March 2016, we treated 14 patients. An isolated PF arthroplasty was performed in six knees (five patients), and a combined PF and unicompartmental knee arthroplasty was performed in nine cases. We observed a significant improvement in the clinical and functional Knee Society Scores (KSSs) after surgery in our patients. Results We obtained good results in our cases both for clinical and functional KSSs. Patellar clunk was recorded in one case. Discussion and Conclusion We are going toward a new attitude in which partial osteoarthritic changes could be treated with partial resurfacing prosthetic solutions such as unicompartmental, bi–unicompartmental or PFR alone, or unicompartmental combined, which respects the cruciates and achieves maximal bone preservation, which is vital, particularly, for young patients
Observing heme doming in myoglobin with femtosecond X-ray absorption spectroscopy
We report time-resolved X-ray absorption measurements after photolysis of carbonmonoxy myoglobin performed at the LCLS X-ray free electron laser with nearly 100 fs (FWHM) time resolution. Data at the Fe K-edge reveal that the photoinduced structural changes at the heme occur in two steps, with a faster (∼70 fs) relaxation preceding a slower (∼400 fs) one. We tentatively attribute the first relaxation to a structural rearrangement induced by photolysis involving essentially only the heme chromophore and the second relaxation to a residual Fe motion out of the heme plane that is coupled to the displacement of myoglobin F-helix
IPOMAGNESEMIA GRAVE CORRELATA ALL’ASSUNZIONE DI INIBITORE DI POMPA PROTONICA
Gli inibitori di pompa protonica (IPP) sono tra i farmaci più frequentemente assunti nella popolazione anziana, spesso cronicamente, anche per indicazioni non sempre giustificate. Sebbene siano farmaci ben tollerati, emergono sempre nuove e frequenti reazioni avverse. In particolare, negli ultimi anni, sono stati riportati vari case-report di ipomagnesemia insorta dopo terapia prolungata con IPP. Tuttavia, ad oggi, non è stato di-mostrato il meccanismo fisiopatologico con cui queste molecole possono indurre tale disionia. Il magnesio è il secondo catione più abbondante nella cellula e svolge ruoli chiave in molti processi intracellulari. La sua omeostasi è garantita dall’equilibrio tra l’assorbimento intestinale e l’escrezione (e riassorbimento) renale, non-ché dallo scambio con l’osso, che rappresenta più del-la metà dei suoi depositi. L’ipomagnesemia severa può causare tetania, convulsioni, aritmie cardiache, ipoparatiroidismo ed ipocalcemia/ipokaliemia. L’assorbi-mento del magnesio avviene nell’intestino in due modi: passivamente secondo gradiente di concentrazione (attraverso gli spazi paracellulari della mucosa nel piccolo intestino) e attivamente (quasi esclusivamente nel colon e nel tubulo contorto distale del rene) tramite dei trasportatori transcellulari saturabili, appartenenti alla famiglia delle proteine di canale (TRP) e chiamati TRPM6 e TRPM7. Si è ipotizzato che il deficit di magnesio associato a terapia con IPP possa essere dovuto più ad un malassorbimento intestinale del catione che ad una sua perdita renale, in quanto, nei casi riportati, la magnesuria è risultata ridotta. Descriviamo il caso di un uomo di 74 anni ricoverato presso l’U.O.C. di Geriatria del Policlinico Universitario di Palermo nel mese di marzo 2017 per grave ipocalcemia e ipomagnesemia
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