35 research outputs found
Research Priorities for Achieving Healthy Marine Ecosystems and Human Communities in a Changing Climate
ABSTRACT: The health of coastal human communities and marine ecosystems are at risk from a host of anthropogenic stressors, in particular, climate change. Because ecological health and human well-being are inextricably connected, effective and positive responses to current risks require multidisciplinary solutions. Yet, the complexity of coupled social-ecological systems has left many potential solutions unidentified or insufficiently explored. The urgent need to achieve positive social and ecological outcomes across local and global scales necessitates rapid and targeted multidisciplinary research to identify solutions that have the greatest chance of promoting benefits for both people and nature. To address these challenges, we conducted a forecasting exercise with a diverse, multidisciplinary team to identify priority research questions needed to promote sustainable and just marine social-ecological systems now and into the future, within the context of climate change and population growth. In contrast to the traditional reactive cycle of science and management, we aimed to generate questions that focus on what we need to know, before we need to know it. Participants were presented with the question, "If we were managing oceans in 2050 and looking back, what research, primary or synthetic, would wish we had invested in today?" We first identified major social and ecological events over the past 60 years that shaped current human relationships with coasts and oceans. We then used a modified Delphi approach to identify nine priority research areas and 46 questions focused on increasing sustainability and well-being in marine social-ecological systems. The research areas we identified include relationships between ecological and human health, access to resources, equity, governance, economics, resilience, and technology. Most questions require increased collaboration across traditionally distinct disciplines and sectors for successful study and implementation. By identifying these questions, we hope to facilitate the discourse, research, and policies needed to rapidly promote healthy marine ecosystems and the human communities that depend upon them
A genealogy of hacking
Hacking is now a widely discussed and known phenomenon, but remains difficult to define and empirically identify because it has come to refer to many different, sometimes incompatible, material practices. This paper proposes genealogy as a framework for understanding hacking by briefly revisiting Foucault’s concept of genealogy and interpreting its perspectival stance through the feminist materialist concept of the situated observer. Using genealogy as a theoretical frame a history of hacking will be proposed in four phases. The first phase is the ‘pre-history’ of hacking in which four core practices were developed. The second phase is the ‘golden age of cracking’ in which hacking becomes a self-conscious identity and community and is for many identified with breaking into computers, even while non-cracking practices such as free software mature. The third phase sees hacking divide into a number of new practices even while old practices continue, including the rise of serious cybercrime, hacktivism, the division of Open Source and Free Software and hacking as an ethic of business and work. The final phase sees broad consciousness of state-sponsored hacking, the re-rise of hardware hacking in maker labs and hack spaces and the diffusion of hacking into a broad ‘clever’ practice. In conclusion it will be argued that hacking consists across all the practices surveyed of an interrogation of the rationality of information techno-cultures enacted by each hacker practice situating itself within a particular techno-culture and then using that techno-culture to change itself, both in changing potential actions that can be taken and changing the nature of the techno-culture itself
Long-term Mortality in HIV-Positive Individuals Virally Suppressed for >3 Years With Incomplete CD4 Recovery
Virally suppressed HIV-positive individuals on combination antiretroviral therapy who do not achieve a CD4 count >200 cells/µL have substantially increased long-term mortality. The increased mortality was seen across different patient groups and for all causes of deat
CD4:CD8 ratio and CD8 count as prognostic markers for mortality in HIV-positive patients on ART:Antiretroviral Therapy Cohort Collaboration
We investigated whether CD4:CD8 ratio and CD8 count were prognostic for all-cause, AIDS, and non-AIDS mortality in virologically suppressed patients with high CD4 count.
We used data from 13 European and North American cohorts of human immunodeficiency virus-infected, antiretroviral therapy (ART)-naive adults who started ART during 1996-2010, who were followed from the date they had CD4 count ≥350 cells/μL and were virologically suppressed (baseline). We used stratified Cox models to estimate unadjusted and adjusted (for sex, people who inject drugs, ART initiation year, and baseline age, CD4 count, AIDS, duration of ART) all-cause and cause-specific mortality hazard ratios for tertiles of CD4:CD8 ratio (0-0.40, 0.41-0.64 [reference], >0.64) and CD8 count (0-760, 761-1138 [reference], >1138 cells/μL) and examined the shape of associations using cubic splines.
During 276526 person-years, 1834 of 49865 patients died (249 AIDS-related; 1076 non-AIDS-defining; 509 unknown/unclassifiable deaths). There was little evidence that CD4:CD8 ratio was prognostic for all-cause mortality after adjustment for other factors: the adjusted hazard ratio (aHR) for lower vs middle tertile was 1.11 (95% confidence interval [CI], 1.00-1.25). The association of CD8 count with all-cause mortality was U-shaped: aHR for higher vs middle tertile was 1.13 (95% CI, 1.01-1.26). AIDS-related mortality declined with increasing CD4:CD8 ratio and decreasing CD8 count. There was little evidence that CD4:CD8 ratio or CD8 count was prognostic for non-AIDS mortality.
In this large cohort collaboration, the magnitude of adjusted associations of CD4:CD8 ratio or CD8 count with mortality was too small for them to be useful as independent prognostic markers in virally suppressed patients on ART
Measurement-Induced State Transitions in a Superconducting Qubit: Within the Rotating Wave Approximation
Superconducting qubits typically use a dispersive readout scheme, where a
resonator is coupled to a qubit such that its frequency is qubit-state
dependent. Measurement is performed by driving the resonator, where the
transmitted resonator field yields information about the resonator frequency
and thus the qubit state. Ideally, we could use arbitrarily strong resonator
drives to achieve a target signal-to-noise ratio in the shortest possible time.
However, experiments have shown that when the average resonator photon number
exceeds a certain threshold, the qubit is excited out of its computational
subspace, which we refer to as a measurement-induced state transition. These
transitions degrade readout fidelity, and constitute leakage which precludes
further operation of the qubit in, for example, error correction. Here we study
these transitions using a transmon qubit by experimentally measuring their
dependence on qubit frequency, average photon number, and qubit state, in the
regime where the resonator frequency is lower than the qubit frequency. We
observe signatures of resonant transitions between levels in the coupled
qubit-resonator system that exhibit noisy behavior when measured repeatedly in
time. We provide a semi-classical model of these transitions based on the
rotating wave approximation and use it to predict the onset of state
transitions in our experiments. Our results suggest the transmon is excited to
levels near the top of its cosine potential following a state transition, where
the charge dispersion of higher transmon levels explains the observed noisy
behavior of state transitions. Moreover, occupation in these higher energy
levels poses a major challenge for fast qubit reset
Overcoming leakage in scalable quantum error correction
Leakage of quantum information out of computational states into higher energy
states represents a major challenge in the pursuit of quantum error correction
(QEC). In a QEC circuit, leakage builds over time and spreads through
multi-qubit interactions. This leads to correlated errors that degrade the
exponential suppression of logical error with scale, challenging the
feasibility of QEC as a path towards fault-tolerant quantum computation. Here,
we demonstrate the execution of a distance-3 surface code and distance-21
bit-flip code on a Sycamore quantum processor where leakage is removed from all
qubits in each cycle. This shortens the lifetime of leakage and curtails its
ability to spread and induce correlated errors. We report a ten-fold reduction
in steady-state leakage population on the data qubits encoding the logical
state and an average leakage population of less than
throughout the entire device. The leakage removal process itself efficiently
returns leakage population back to the computational basis, and adding it to a
code circuit prevents leakage from inducing correlated error across cycles,
restoring a fundamental assumption of QEC. With this demonstration that leakage
can be contained, we resolve a key challenge for practical QEC at scale.Comment: Main text: 7 pages, 5 figure
Measurement-induced entanglement and teleportation on a noisy quantum processor
Measurement has a special role in quantum theory: by collapsing the
wavefunction it can enable phenomena such as teleportation and thereby alter
the "arrow of time" that constrains unitary evolution. When integrated in
many-body dynamics, measurements can lead to emergent patterns of quantum
information in space-time that go beyond established paradigms for
characterizing phases, either in or out of equilibrium. On present-day NISQ
processors, the experimental realization of this physics is challenging due to
noise, hardware limitations, and the stochastic nature of quantum measurement.
Here we address each of these experimental challenges and investigate
measurement-induced quantum information phases on up to 70 superconducting
qubits. By leveraging the interchangeability of space and time, we use a
duality mapping, to avoid mid-circuit measurement and access different
manifestations of the underlying phases -- from entanglement scaling to
measurement-induced teleportation -- in a unified way. We obtain finite-size
signatures of a phase transition with a decoding protocol that correlates the
experimental measurement record with classical simulation data. The phases
display sharply different sensitivity to noise, which we exploit to turn an
inherent hardware limitation into a useful diagnostic. Our work demonstrates an
approach to realize measurement-induced physics at scales that are at the
limits of current NISQ processors
A obliteração da cultura e a naturalização da escolha nas confabulações da psicologia evolucionista
Non-Abelian braiding of graph vertices in a superconducting processor
Indistinguishability of particles is a fundamental principle of quantum
mechanics. For all elementary and quasiparticles observed to date - including
fermions, bosons, and Abelian anyons - this principle guarantees that the
braiding of identical particles leaves the system unchanged. However, in two
spatial dimensions, an intriguing possibility exists: braiding of non-Abelian
anyons causes rotations in a space of topologically degenerate wavefunctions.
Hence, it can change the observables of the system without violating the
principle of indistinguishability. Despite the well developed mathematical
description of non-Abelian anyons and numerous theoretical proposals, the
experimental observation of their exchange statistics has remained elusive for
decades. Controllable many-body quantum states generated on quantum processors
offer another path for exploring these fundamental phenomena. While efforts on
conventional solid-state platforms typically involve Hamiltonian dynamics of
quasi-particles, superconducting quantum processors allow for directly
manipulating the many-body wavefunction via unitary gates. Building on
predictions that stabilizer codes can host projective non-Abelian Ising anyons,
we implement a generalized stabilizer code and unitary protocol to create and
braid them. This allows us to experimentally verify the fusion rules of the
anyons and braid them to realize their statistics. We then study the prospect
of employing the anyons for quantum computation and utilize braiding to create
an entangled state of anyons encoding three logical qubits. Our work provides
new insights about non-Abelian braiding and - through the future inclusion of
error correction to achieve topological protection - could open a path toward
fault-tolerant quantum computing
Suppressing quantum errors by scaling a surface code logical qubit
Practical quantum computing will require error rates that are well below what
is achievable with physical qubits. Quantum error correction offers a path to
algorithmically-relevant error rates by encoding logical qubits within many
physical qubits, where increasing the number of physical qubits enhances
protection against physical errors. However, introducing more qubits also
increases the number of error sources, so the density of errors must be
sufficiently low in order for logical performance to improve with increasing
code size. Here, we report the measurement of logical qubit performance scaling
across multiple code sizes, and demonstrate that our system of superconducting
qubits has sufficient performance to overcome the additional errors from
increasing qubit number. We find our distance-5 surface code logical qubit
modestly outperforms an ensemble of distance-3 logical qubits on average, both
in terms of logical error probability over 25 cycles and logical error per
cycle ( compared to ). To investigate
damaging, low-probability error sources, we run a distance-25 repetition code
and observe a logical error per round floor set by a single
high-energy event ( when excluding this event). We are able
to accurately model our experiment, and from this model we can extract error
budgets that highlight the biggest challenges for future systems. These results
mark the first experimental demonstration where quantum error correction begins
to improve performance with increasing qubit number, illuminating the path to
reaching the logical error rates required for computation.Comment: Main text: 6 pages, 4 figures. v2: Update author list, references,
Fig. S12, Table I