2,774 research outputs found
Ultrafast optical ranging using microresonator soliton frequency combs
Light detection and ranging (LIDAR) is critical to many fields in science and
industry. Over the last decade, optical frequency combs were shown to offer
unique advantages in optical ranging, in particular when it comes to fast
distance acquisition with high accuracy. However, current comb-based concepts
are not suited for emerging high-volume applications such as drone navigation
or autonomous driving. These applications critically rely on LIDAR systems that
are not only accurate and fast, but also compact, robust, and amenable to
cost-efficient mass-production. Here we show that integrated dissipative
Kerr-soliton (DKS) comb sources provide a route to chip-scale LIDAR systems
that combine sub-wavelength accuracy and unprecedented acquisition speed with
the opportunity to exploit advanced photonic integration concepts for
wafer-scale mass production. In our experiments, we use a pair of free-running
DKS combs, each providing more than 100 carriers for massively parallel
synthetic-wavelength interferometry. We demonstrate dual-comb distance
measurements with record-low Allan deviations down to 12 nm at averaging times
of 14 s as well as ultrafast ranging at unprecedented measurement rates of
up to 100 MHz. We prove the viability of our technique by sampling the
naturally scattering surface of air-gun projectiles flying at 150 m/s (Mach
0.47). Combining integrated dual-comb LIDAR engines with chip-scale
nanophotonic phased arrays, the approach could allow widespread use of compact
ultrafast ranging systems in emerging mass applications.Comment: 9 pages, 3 figures, Supplementary information is attached in
'Ancillary files
Microresonator solitons for massively parallel coherent optical communications
Optical solitons are waveforms that preserve their shape while propagating,
relying on a balance of dispersion and nonlinearity. Soliton-based data
transmission schemes were investigated in the 1980s, promising to overcome the
limitations imposed by dispersion of optical fibers. These approaches, however,
were eventually abandoned in favor of wavelength-division multiplexing (WDM)
schemes that are easier to implement and offer improved scalability to higher
data rates. Here, we show that solitons may experience a comeback in optical
communications, this time not as a competitor, but as a key element of
massively parallel WDM. Instead of encoding data on the soliton itself, we
exploit continuously circulating dissipative Kerr solitons (DKS) in a
microresonator. DKS are generated in an integrated silicon nitride
microresonator by four-photon interactions mediated by Kerr nonlinearity,
leading to low-noise, spectrally smooth and broadband optical frequency combs.
In our experiments, we use two interleaved soliton Kerr combs to transmit a
data stream of more than 50Tbit/s on a total of 179 individual optical carriers
that span the entire telecommunication C and L bands. Equally important, we
demonstrate coherent detection of a WDM data stream by using a pair of
microresonator Kerr soliton combs - one as a multi-wavelength light source at
the transmitter, and another one as a corresponding local oscillator (LO) at
the receiver. This approach exploits the scalability advantages of
microresonator soliton comb sources for massively parallel optical
communications both at the transmitter and receiver side. Taken together, the
results prove the significant potential of these sources to replace arrays of
continuous-wave lasers in high-speed communications.Comment: 10 pages, 3 figure
Antitumor Tâcell function requires CPEB4âmediated adaptation to chronic endoplasmic reticulum stress
Tumor growth is influenced by a complex network of interactions between multiple cell types in the tumor microenvironment (TME). These constrained conditions trigger the endoplasmic reticulum (ER) stress response, which extensively reprograms mRNA translation. When uncontrolled over time, chronic ER stress impairs the antitumor effector function of CD8 T lymphocytes. How cells promote adaptation to chronic stress in the TME without the detrimental effects of the terminal unfolded protein response (UPR) is unknown. Here, we find that, in effector CD8 T lymphocytes, RNA-binding protein CPEB4 constitutes a new branch of the UPR that allows cells to adapt to sustained ER stress, yet remains decoupled from the terminal UPR. ER stress, induced during CD8 T-cell activation and effector function, triggers CPEB4 expression. CPEB4 then mediates chronic stress adaptation to maintain cellular fitness, allowing effector molecule production and cytotoxic activity. Accordingly, this branch of the UPR is required for the antitumor effector function of T lymphocytes, and its disruption in these cells exacerbates tumor growth.© 2023 The Authors. Published under the terms of the CC BY NC ND 4.0 license
The pitfalls of plural valuation
This paper critically examines the current political context in which valuation studies of nature are undertaken. It challenges the belief that somehow, more and technically better valuation will drive the societal change toward more just and sustainable futures. Instead, we argue that current and proposed valuation practices risk to continue to overrepresent the values of those who hold power and dominate the valuation space, and to perpetuate the discrimination of the views and values of nondominant stakeholders. In tackling this politically sensitive issue, we define a political typology of valuations, making explicit the roles of power and discrimination. This is done to provide valuation professionals and other actors with a simple framework to determine if valuation actions and activities are constructive, inclusive, resolve injustices and enable systemic change, or rather entrench the status quo or aggravate existing injustices. The objective is to buttress actors in their decisions to support, accept, improve, oppose, or reject such valuations
Establishing a Reference Baseline for Midday Stem Water Potential in Olive and Its Use for Plant-Based Irrigation Management
Midday stem water potential (SWP) is rapidly becoming adopted as a standard tool for plant-based irrigation management in many woody perennial crops. A reference or âbaselineâ SWP has been used in some crops (almond, prune, grape, and walnut) to account for the climatic influence of air vapor pressure deficit (VPD) on SWP under non-limiting soil moisture conditions. The baseline can be determined empirically for field trees maintained under such non-limiting conditions, but such conditions are difficult to achieve for an entire season. We present the results of an alternative survey-based approach, using a large set of SWP and VPD data collected over multiple years, from irrigation experiments in olive orchards located in multiple countries [Spain, United States (California), Italy, and Argentina]. The relation of SWP to midday VPD across the entire data set was consistent with an upper limit SWP which declined with VPD, with the upper limit being similar to that found in Prunus. A best fit linear regression estimate for this upper limit (baseline) was found by selecting the maximum R2 and minimum probability for various upper fractions of the SWP/VPD relation. In addition to being surprisingly similar to the Prunus baseline, the olive baseline was also similar (within 0.1 MPa) to a recently published mechanistic olive soil-plant-atmosphere-continuum (SPAC) model for âsuper high densityâ orchard systems. Despite similarities in the baseline, the overall physiological range of SWP exhibited by olive extends to about â8 MPa, compared to about â4 MPa for economically producing almond. This may indicate that, despite species differences in physiological responses to low water availability (drought), there may be convergent adaptations/acclimations across species to high levels of water availability. Similar to its use in other crops, the olive baseline will enable more accurate and reproducible plant-based irrigation management for both full and deficit irrigation practices, and we present tentative SWP guidelines for this purpose
Searching for Exoplanets Using a Microresonator Astrocomb
Detection of weak radial velocity shifts of host stars induced by orbiting
planets is an important technique for discovering and characterizing planets
beyond our solar system. Optical frequency combs enable calibration of stellar
radial velocity shifts at levels required for detection of Earth analogs. A new
chip-based device, the Kerr soliton microcomb, has properties ideal for
ubiquitous application outside the lab and even in future space-borne
instruments. Moreover, microcomb spectra are ideally suited for astronomical
spectrograph calibration and eliminate filtering steps required by conventional
mode-locked-laser frequency combs. Here, for the calibration of astronomical
spectrographs, we demonstrate an atomic/molecular line-referenced,
near-infrared soliton microcomb. Efforts to search for the known exoplanet HD
187123b were conducted at the Keck-II telescope as a first in-the-field
demonstration of microcombs
Exploring the usefulness of scenario archetypes in science-policy processes: experience across IPBES assessments
Scenario analyses have been used in multiple science-policy assessments to better understand complex plausible futures. Scenario archetype approaches are based on the fact that many future scenarios have similar underlying storylines, assumptions, and trends in drivers of change, which allows for grouping of scenarios into typologies, or archetypes, facilitating comparisons between a large range of studies. The use of scenario archetypes in environmental assessments foregrounds important policy questions and can be used to codesign interventions tackling future sustainability issues. Recently, scenario archetypes were used in four regional assessments and one ongoing global assessment within the Intergovernmental Science-Policy Platform for Biodiversity and Ecosystem Services (IPBES). The aim of these assessments was to provide decision makers with policy-relevant knowledge about the state of biodiversity, ecosystems, and the contributions they provide to people. This paper reflects on the usefulness of the scenario archetype approach within science-policy processes, drawing on the experience from the IPBES assessments. Using a thematic analysis of (a) survey data collected from experts involved in the archetype analyses across IPBES assessments, (b) notes from IPBES workshops, and (c) regional assessment chapter texts, we synthesize the benefits, challenges, and frontiers of applying the scenario archetype approach in a science-policy process. Scenario archetypes were perceived to allow syntheses of large amounts of information for scientific, practice-, and policy-related purposes, streamline key messages from multiple scenario studies, and facilitate communication of them to end users. In terms of challenges, they were perceived as subjective in their interpretation, oversimplifying information, having a limited applicability across scales, and concealing contextual information and novel narratives. Finally, our results highlight what methodologies, applications, and frontiers in archetype-based research should be explored in the future. These advances can assist the design of future large-scale sustainability-related assessment processes, aiming to better support decisions and interventions for equitable and sustainable futures
Multiplicity dependence of jet-like two-particle correlations in p-Pb collisions at = 5.02 TeV
Two-particle angular correlations between unidentified charged trigger and
associated particles are measured by the ALICE detector in p-Pb collisions at a
nucleon-nucleon centre-of-mass energy of 5.02 TeV. The transverse-momentum
range 0.7 5.0 GeV/ is examined,
to include correlations induced by jets originating from low
momen\-tum-transfer scatterings (minijets). The correlations expressed as
associated yield per trigger particle are obtained in the pseudorapidity range
. The near-side long-range pseudorapidity correlations observed in
high-multiplicity p-Pb collisions are subtracted from both near-side
short-range and away-side correlations in order to remove the non-jet-like
components. The yields in the jet-like peaks are found to be invariant with
event multiplicity with the exception of events with low multiplicity. This
invariance is consistent with the particles being produced via the incoherent
fragmentation of multiple parton--parton scatterings, while the yield related
to the previously observed ridge structures is not jet-related. The number of
uncorrelated sources of particle production is found to increase linearly with
multiplicity, suggesting no saturation of the number of multi-parton
interactions even in the highest multiplicity p-Pb collisions. Further, the
number scales in the intermediate multiplicity region with the number of binary
nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation.Comment: 23 pages, 6 captioned figures, 1 table, authors from page 17,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/161
Multi-particle azimuthal correlations in p-Pb and Pb-Pb collisions at the CERN Large Hadron Collider
Measurements of multi-particle azimuthal correlations (cumulants) for charged
particles in p-Pb and Pb-Pb collisions are presented. They help address the
question of whether there is evidence for global, flow-like, azimuthal
correlations in the p-Pb system. Comparisons are made to measurements from the
larger Pb-Pb system, where such evidence is established. In particular, the
second harmonic two-particle cumulants are found to decrease with multiplicity,
characteristic of a dominance of few-particle correlations in p-Pb collisions.
However, when a gap is placed to suppress such correlations,
the two-particle cumulants begin to rise at high-multiplicity, indicating the
presence of global azimuthal correlations. The Pb-Pb values are higher than the
p-Pb values at similar multiplicities. In both systems, the second harmonic
four-particle cumulants exhibit a transition from positive to negative values
when the multiplicity increases. The negative values allow for a measurement of
to be made, which is found to be higher in Pb-Pb collisions at
similar multiplicities. The second harmonic six-particle cumulants are also
found to be higher in Pb-Pb collisions. In Pb-Pb collisions, we generally find
which is indicative of a Bessel-Gaussian
function for the distribution. For very high-multiplicity Pb-Pb
collisions, we observe that the four- and six-particle cumulants become
consistent with 0. Finally, third harmonic two-particle cumulants in p-Pb and
Pb-Pb are measured. These are found to be similar for overlapping
multiplicities, when a gap is placed.Comment: 25 pages, 11 captioned figures, 3 tables, authors from page 20,
published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/87
The pitfalls of plural valuation
This paper critically examines the current political context in which valuation studies of nature are undertaken. It challenges the belief that somehow, more and technically better valuation will drive the societal change toward more just and sustainable futures. Instead, we argue that current and proposed valuation practices risk to continue to overrepresent the values of those who hold power and dominate the valuation space, and to perpetuate the discrimination of the views and values of nondominant stakeholders. In tackling this politically sensitive issue, we define a political typology of valuations, making explicit the roles of power and discrimination. This is done to provide valuation professionals and other actors with a simple framework to determine if valuation actions and activities are constructive, inclusive, resolve injustices and enable systemic change, or rather entrench the status quo or aggravate existing injustices. The objective is to buttress actors in their decisions to support, accept, improve, oppose, or reject such valuations
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