Ideally embedded space-times

Due to the growing interest in embeddings of space-time in higher-dimensional spaces we consider a specific type of embedding. After proving an inequality between intrinsically defined curvature invariants and the squared mean curvature, we extend the notion of ideal embeddings from Riemannian geometry to the indefinite case. Ideal embeddings are such that the embedded manifold receives the least amount of tension from the surrounding space. Then it is shown that the de Sitter spaces, a Robertson-Walker space-time and some anisotropic perfect fluid metrics can be ideally embedded in a five-dimensional pseudo-Euclidean space.Comment: layout changed and typos corrected; uses revtex

Quantum radiation in a plane cavity with moving mirrors

We consider the electromagnetic vacuum field inside a perfect plane cavity with moving mirrors, in the nonrelativistic approximation. We show that low frequency photons are generated in pairs that satisfy simple properties associated to the plane geometry. We calculate the photon generation rates for each polarization as functions of the mechanical frequency by two independent methods: on one hand from the analysis of the boundary conditions for moving mirrors and with the aid of Green functions; and on the other hand by an effective Hamiltonian approach. The angular and frequency spectra are discrete, and emission rates for each allowed angular direction are obtained. We discuss the dependence of the generation rates on the cavity length and show that the effect is enhanced for short cavity lengths. We also compute the dissipative force on the moving mirrors and show that it is related to the total radiated energy as predicted by energy conservation.Comment: 17 pages, 1 figure, published in Physical Review

Inertial forces in the Casimir effect with two moving plates

We combine linear response theory and dimensional regularization in order to derive the dynamical Casimir force in the low frequency regime. We consider two parallel plates moving along the normal direction in $D-$dimensional space. We assume the free-space values for the mass of each plate to be known, and obtain finite, separation-dependent mass corrections resulting from the combined effect of the two plates. The global mass correction is proportional to the static Casimir energy, in agreement with Einstein's law of equivalence between mass and energy for stressed rigid bodies.Comment: 9 pages, 1 figure; title and abstract changed; to appear in Physical Review

Expression Of Mcl-1 And Ki-67 In Papillary Thyroid Carcinomas

Studying molecules that are differentially expressed in cancers as well as benign and normal tissues is crucial for identifying novel bio-markers for cancer immunotherapy. This study aimed to investigate the clinical utility of the immunochemical expression of the proliferative cell marker Ki-67 and the apoptotic blocker Mcl-1 in papillary thyroid carcinoma (PTC). Methods: We built a tissue microarray with 282 thyroid specimens. There were 59 PTCs including 35 classic (CPTC), 3 tall cell (TCPTC) and 21 follicular variants (FVPTC); 79 benign thyroid diseases (22 follicular adenomas; 57 adenomatoid hyperplasia); 33 Hashimoto's thyroiditis (HT) specimens; and 111 normal thyroid tissues. Clinical history and ultrasound data were retrospectively obtained by chart review. Results: Mcl-1 overexpression was evident in 66.7% of the PTC tissues compared to 32% of the benign thyroid diseases. Mcl-1 strong staining distinguished benign from malignant thyroid lesions (sensitivity = 61.3%; specificity = 72.8%; negative predictive value, NPV = 68%; positive predictive value, PPV = 66.7% and 67.5% accuracy). Positive nuclear Ki-67 staining was observed in 34% of PTCs vs. 19% of thyroid adenomas (P = 0.031). Strong Mcl-1 and Ki-67 co-expression was identified in 57.5% of PTCs with a higher PPV (75.8%). Mcl-1 and Ki-67 expression was not associated with any clinicopathological feature of malignancy. No deaths occurred during the follow-up. Conclusions: Mcl-1 immunochemical overexpression allowed differentiating low-risk PTC from the benign thyroid lesions. We suggest that Mcl-1 expression may help differentiate follicular patterned thyroid lesions. The influence of the Mcl-1 expression on several features of tumor aggressiveness has to be studied in large series of high-risk thyroid carcinomas.124420921

Just follow the suit! Trust in human-robot interactions during card game playing

Robots are currently being developed to enter our lives and interact with us in different tasks. For humans to be able to have a positive experience of interaction with such robots, they need to trust them to some degree. In this paper, we present the development and evaluation of a social robot that was created to play a card game with humans, playing the role of a partner and opponent. This type of activity is especially important, since our target group is elderly people - a population that often suffers from social isolation. Moreover, the card game scenario can lead to the development of interesting trust dynamics during the interaction, in which the human that partners with the robot needs to trust it in order to succeed and win the game. The design of the robot's behavior and game dynamics was inspired in previous user-centered design studies in which elderly people played the same game. Our evaluation results show that the levels of trust differ according to the previous knowledge that players have of their partners. Thus, humans seem to significantly increase their trust level towards a robot they already know, whilst maintaining the same level of trust in a human that they also previously knew. Henceforth, this paper shows that trust is a multifaceted construct that develops differently for humans and robots.info:eu-repo/semantics/acceptedVersio

Casimir forces between arbitrary compact objects: Scalar and electromagnetic field

We develop an exact method for computing the Casimir energy between arbitrary compact objects, both with boundary conditions for a scalar field and dielectrics or perfect conductors for the electromagnetic field. The energy is obtained as an interaction between multipoles, generated by quantum source or current fluctuations. The objects' shape and composition enter only through their scattering matrices. The result is exact when all multipoles are included, and converges rapidly. A low frequency expansion yields the energy as a series in the ratio of the objects' size to their separation. As examples, we obtain this series for two spheres with Robin boundary conditions for a scalar field and dielectric spheres for the electromagnetic field. The full interaction at all separations is obtained for spheres with Robin boundary conditions and for perfectly conducting spheres.Comment: 24 pages, 3 figures, contribution to QFEXT07 proceeding