RESUMO
We explore the relaxation dynamics of elementary spin clusters in a kinetically constrained spin system. Inspired by experiments with Rydberg lattice gases, we focus on the situation in which an excited spin leads to a "facilitated" excitation of a neighboring spin. We show that even weak interactions that extend beyond nearest neighbors can have a dramatic impact on the relaxation behavior: they generate a linear potential, which under certain conditions leads to the onset of Bloch oscillations of spin clusters. These hinder the expansion of a cluster and, more generally, the relaxation of many-body states toward equilibrium. This shows that nonergodic behavior in kinetically constrained systems may occur as a consequence of the interplay between reduced connectivity of many-body states and weak interparticle interactions. We furthermore show that the emergent Bloch oscillations identified here can be detected in experiment through measurements of the Rydberg atom density and discuss how spin-orbit coupling between internal and external degrees of freedom of spin clusters can be used to control their relaxation behavior.
RESUMO
Quantum spin systems with kinetic constraints have become paradigmatic for exploring collective dynamical behavior in many-body systems. Here we discuss a facilitated spin system which is inspired by recent progress in the realization of Rydberg quantum simulators. This platform allows to control and investigate the interplay between facilitation dynamics and the coupling of spin degrees of freedom to lattice vibrations. Developing a minimal model, we show that this leads to the formation of polaronic quasiparticle excitations which are formed by many-body spin states dressed by phonons. We investigate in detail the properties of these quasiparticles, such as their dispersion relation, effective mass, and the quasiparticle weight. Rydberg lattice quantum simulators are particularly suited for studying this phonon-dressed kinetically constrained dynamics as their exaggerated length scales permit the site-resolved monitoring of spin and phonon degrees of freedom.
RESUMO
BACKGROUND AND AIMS: Sentinel node biopsy is currently used in surgery of malignant melanoma and breast cancer. The feasibility of sentinel node mapping in gastrointestinal cancers and its diagnostic sensitivity is unclear. It could be of particular value in the management of early gastric cancer in which radical D2 lymphadenectomy may be unnecessary. MATERIALS AND METHODS: From January 2004 to June 2005, ten patients with preoperative diagnosis of early gastric cancer and no nodal involvement (cT1N0) were submitted to sentinel node biopsy using the dual mapping procedure with endoscopic blue dye and 99mTc radio colloid injection. All the patients underwent standard radical gastrectomy and D2 lymphadenectomy. The resected nodes were evaluated by routine (hematoxylin-eosin) histopathological examination; the sentinel (blue or hot) nodes, in addition, were evaluated with immunohistochemistry for cytokeratin. RESULTS: The detection rate of this procedure was 100%. The preliminary results and perspectives for feasibility of sentinel node biopsy and its accuracy in predicting the nodal status in early gastric cancer are discussed.