203 research outputs found
The Computational Power of Minkowski Spacetime
The Lorentzian length of a timelike curve connecting both endpoints of a
classical computation is a function of the path taken through Minkowski
spacetime. The associated runtime difference is due to time-dilation: the
phenomenon whereby an observer finds that another's physically identical ideal
clock has ticked at a different rate than their own clock. Using ideas
appearing in the framework of computational complexity theory, time-dilation is
quantified as an algorithmic resource by relating relativistic energy to an
th order polynomial time reduction at the completion of an observer's
journey. These results enable a comparison between the optimal quadratic
\emph{Grover speedup} from quantum computing and an speedup using
classical computers and relativistic effects. The goal is not to propose a
practical model of computation, but to probe the ultimate limits physics places
on computation.Comment: 6 pages, LaTeX, feedback welcom
Fault Models for Quantum Mechanical Switching Networks
The difference between faults and errors is that, unlike faults, errors can
be corrected using control codes. In classical test and verification one
develops a test set separating a correct circuit from a circuit containing any
considered fault. Classical faults are modelled at the logical level by fault
models that act on classical states. The stuck fault model, thought of as a
lead connected to a power rail or to a ground, is most typically considered. A
classical test set complete for the stuck fault model propagates both binary
basis states, 0 and 1, through all nodes in a network and is known to detect
many physical faults. A classical test set complete for the stuck fault model
allows all circuit nodes to be completely tested and verifies the function of
many gates. It is natural to ask if one may adapt any of the known classical
methods to test quantum circuits. Of course, classical fault models do not
capture all the logical failures found in quantum circuits. The first obstacle
faced when using methods from classical test is developing a set of realistic
quantum-logical fault models. Developing fault models to abstract the test
problem away from the device level motivated our study. Several results are
established. First, we describe typical modes of failure present in the
physical design of quantum circuits. From this we develop fault models for
quantum binary circuits that enable testing at the logical level. The
application of these fault models is shown by adapting the classical test set
generation technique known as constructing a fault table to generate quantum
test sets. A test set developed using this method is shown to detect each of
the considered faults.Comment: (almost) Forgotten rewrite from 200
Iron Metabolism in the Tumor Microenvironment-Implications for Anti-Cancer Immune Response
New insights into the field of iron metabolism within the tumor microenvironment have been uncovered in recent years. Iron promotes the production of reactive oxygen species, which may either trigger ferroptosis cell death or contribute to malignant transformation. Once transformed, cancer cells divert tumor-infiltrating immune cells to satisfy their iron demand, thus affecting the tumor immunosurveillance. In this review, we highlight how the bioavailability of this metal shapes complex metabolic pathways within the tumor microenvironment and how this affects both tumor-associated macrophages and tumor-infiltrating lymphocytes functions. Furthermore, we discuss the potentials as well as the current clinical controversies surrounding the use of iron metabolism as a target for new anticancer treatments in two opposed conditions: i) the "hot" tumors, which are usually enriched in immune cells infiltration and are extremely rich in iron availability within the microenvironment, and ii) the "cold" tumors, which are often very poor in immune cells, mainly due to immune exclusion
COVID-19 and schools: what is the risk of contagion? Results of a rapid-antigen-test-based screening campaign in Florence, Italy
INTRODUCTION: in the COVID-19 era, the debate around the risk of contagion at school, is intense in Italy. The Department of Welfare and Wealth of Florence promoted a screening campaign with antigen rapid tests for all the students and school personnel. The aim of this study is to assess the SARS-Cov2 circulation in the school setting by means of a mass screening conducted in every primary and middle school of Florence. METHODS: All the students attending primary and middle schools of Florence and the school personnel were asked to take part. The campaign started on 16(th) November 2020 and was completed on 12(th) February 2021. If the antigen rapid test resulted positive, a molecular test was provided to confirm the result. RESULTS: 18,414 subjects were tested with 15,233 students (82.7%) and 3,181 members of the school personnel (17.3%). Only in 27 cases (0.15%) the rapid test gave a positive result. Moreover, only 14 of the 27 positive rapid tests were confirmed as positive by the molecular test. These results show a very low number of SARS-CoV-2 cases among the people tested (0.08% of the total). CONCLUSIONS: These results show that the spread of SARS-CoV-2 infection at school, during the months of the screening and with the respect of strict preventive measures was low
Computational Complexity of interacting electrons and fundamental limitations of Density Functional Theory
One of the central problems in quantum mechanics is to determine the ground
state properties of a system of electrons interacting via the Coulomb
potential. Since its introduction by Hohenberg, Kohn, and Sham, Density
Functional Theory (DFT) has become the most widely used and successful method
for simulating systems of interacting electrons, making their original work one
of the most cited in physics. In this letter, we show that the field of
computational complexity imposes fundamental limitations on DFT, as an
efficient description of the associated universal functional would allow to
solve any problem in the class QMA (the quantum version of NP) and thus
particularly any problem in NP in polynomial time. This follows from the fact
that finding the ground state energy of the Hubbard model in an external
magnetic field is a hard problem even for a quantum computer, while given the
universal functional it can be computed efficiently using DFT. This provides a
clear illustration how the field of quantum computing is useful even if quantum
computers would never be built.Comment: 8 pages, 3 figures. v2: Version accepted at Nature Physics; differs
significantly from v1 (including new title). Includes an extra appendix (not
contained in the journal version) on the NP-completeness of Hartree-Fock,
which is taken from v
Sign- and magnitude-tunable coupler for superconducting flux qubits
We experimentally confirm the functionality of a coupling element for
flux-based superconducting qubits, with a coupling strength whose sign and
magnitude can be tuned {\it in situ}. To measure the effective , the
groundstate of a coupled two-qubit system has been mapped as a function of the
local magnetic fields applied to each qubit. The state of the system is
determined by directly reading out the individual qubits while tunneling is
suppressed. These measurements demonstrate that can be tuned from
antiferromagnetic through zero to ferromagnetic.Comment: Updated text and figure
Imaging technologies in the differential diagnosis and follow-up of brown tumor in primary hyperparathyroidism: case report and review of the literature
Brown tumors are osteolytic lesions associated with hyperparathyroidism (HPT). They may involve various skeletal segments, but rarely the cranio-facial bones. We report a case of a young boy with a swelling of the jaw secondary to a brown tumor presenting as the first manifestation of primary HPT (PHPT). He was found to have brown tumor located in the skull, as well. Different imaging technologies were employed for the diagnosis and follow-up after parathyroidectomy. We enclose a review of the literature on the employment of such imaging technologies in the differential diagnosis of osteolytic lesions. A multidisciplinary approach comprising clinical, laboratory and imaging findings is essential for the differential diagnosis of brown tumor in PHPT
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