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We report a reduced complexity single polarization all-pass modulation scheme that uses overlap and discard to implement continuous transmission. We find that transmitter NSRs of −25 dB and −21 dB can be achieved with 1/3 and 1/6 the complexity, respectively, of reported solutions. We compare this modulation scheme with a conventional Mach-Zehnder modulator solution by measures of throughput, spectral efficiency, DSP and hardware complexity as well as back-to-back modem margin.

The observation that many lavas associated with mantle plumes have higher 3He/4He ratios than the upper convecting mantle underpins geophysical, geodynamic and geochemical models of Earth’s deep interior. High 3He/4He ratios are thought to derive from the solar nebula or from solar-wind-irradiated material that became incorporated into Earth during early planetary accretion. Traditionally, this high-3He/4He component has been considered intrinsic to the mantle, having avoided outgassing caused by giant impacts and billions of years of mantle convection1–4. Here we report the highest magmatic 3He/4He ratio(67.2 ± 1.8 times the atmospheric ratio) yet measured in terrestrial igneous rocks, in olivines from Baffin Island lavas. We argue that the extremely high-3He/4He helium in these lavas might derive from Earth’s core5–9. The viability of the core hypothesis relaxes the long-standing constraint—based on noble gases in lavas associated with mantle plumes globally—that volatile elements from the solar nebula have survived in the mantle since the early stages of accretion.

Before the Perseverance rover landing, the acoustic environment of Mars was unknown. Models predicted that: (1) atmospheric turbulence changes at centimetre scales or smaller at the point where molecular viscosity converts kinetic energy into heat1, (2) the speed of sound varies at the surface with frequency2,3and (3) high-frequency waves are strongly attenuated with distance in CO2(refs. 2–4). However, theoretical models were uncertain because of a lack of experimental data at low pressure and the difficulty to characterize turbulence or attenuation in a closed environment. Here, using Perseverance microphone recordings, we present the first characterization of the acoustic environment on Mars and pressure fluctuations in the audible range and beyond, from 20 Hz to 50 kHz. We find that atmospheric sounds extend measurements of pressure variations down to 1,000 times smaller scales than ever observed before, showing a dissipative regime extending over five orders of magnitude in energy. Using point sources of sound (Ingenuity rotorcraft, laser-induced sparks), we highlight two distinct values for the speed of sound that are about 10 m s−1apart below and above 240 Hz, a unique characteristic of low-pressure CO2-dominated atmosphere. We also provide the acoustic attenuation with distance above 2 kHz, allowing us to explain the large contribution of the CO2vibrational relaxation in the audible range. These results establish a ground truth for the modelling of acoustic processes, which is critical for studies in atmospheres such as those of Mars and Venus.

High‐resolution 2D and 3D data remotely acquired by SuperCam's Remote Micro‐Imager and Mastcam‐Z aboard the Perseverancerover enabled us to characterize the stratigraphic architecture and sedimentary record of the Kodiak butte, an isolated remnant of the western delta fan of Jezero crater. Using these data, we build up on previous interpretations of the butte interpreted as a prograding Gilbert‐type deltaic series. We characterize three individual stratigraphic Units 0 to 2 on the eastern and northern faces of the butte. Each Unit displays the same vertical succession of prodeltaic/lacustrine bottomsets, delta slope toesets and foresets, and fluvially influenced topsets of a deltaic plain with a braided river pattern, shown by 11 individual sedimentary facies. We infer that these individual Units record the formation of three distinct deltaic mouth bars successively across time and space. For the first time on another planet than Earth, we are able to construct a precise sequence stratigraphic framework to highlight lake‐level fluctuations at the time the Kodiak butte was emplaced, during the latest stages of deltaic activity. We identify four hydrogeological cycles indicated by alternating rises and falls of the lake‐level on the order of 5–10 m. These were most probably linked to climatic events and variations controlling lake water inputs in probable relation to an astronomical control. Kodiak butte is an isolated remnant of the main western sedimentary fan of Jezero crater. It displays the characteristic structures of a Gilbert‐type delta, a structure that shows deposition of fluvial material into a standing body of water, here interpreted to be a lake within Jezero crater. 11 individual sedimentary facies (textures, grain‐sizes, and structures) of the rocks exposed at Kodiak suggest that the depositional environments ranged from the fluvial plain to a steep subaqueous slope and into the bottom of the shallow Jezero lake. Our observations further show that Kodiak butte is organized into three distinct stratigraphic Units (0–2), each displaying the same vertical succession of bottomsets, toesets, foresets and topsets. This architecture is interpreted as reflecting three distinct deltaic packages, formed consecutively and not at the same time. Using these facies and stratigraphic architecture data, we are able for the first time on another planet than Earth, to precisely construct a sequence stratigraphic framework for the formation of Kodiak. This framework illustrates with unprecedented precision successive episodes of rises and falls of the paleo‐lake‐level (in the order of 5–10 m) involved in the construction and evolution of the western Jezero delta. New observations on the Kodiak delta remnant were carried out to characterize its detailed facies and stratigraphic architectureThree deltaic mouth bars are identified showing 4D succession of depositional settings ranging from deltaic plain to slope to shallow lakeThe first ever sequence stratigraphic framework on Mars shows four cycles of alternating rises and falls of the lake‐level within 5–10 m New observations on the Kodiak delta remnant were carried out to characterize its detailed facies and stratigraphic architecture Three deltaic mouth bars are identified showing 4D succession of depositional settings ranging from deltaic plain to slope to shallow lake The first ever sequence stratigraphic framework on Mars shows four cycles of alternating rises and falls of the lake‐level within 5–10 m

(U‐Th)/He geochronology and cosmogenic 3He in iron oxides reveal mineral precipitation ages as old as 55 Ma and exposure ages greater than 5 Ma for canga‐cemented plateaus in the Quadrilátero Ferrífero, Brazil, showing that lateritic profiles overlying banded iron‐formation (BIF) landscapes in tropical regions have a long history of surface exposure. The long‐term erosion history obtained from cosmogenic 3He on BIF plateaus confirms that relic surfaces persist in the landscape for millions of years. Combined 3He and (U‐Th)/He dating shows that cangas are preferentially goethite cemented by biogeochemical reactions in the subsurface. Importantly, pebbles of hematite‐magnetite in colluvia or shallow creeks draining the canga‐cemented plateaus record a much longer exposure history than in situ canga blocks, showing that even older duricrusts, now eroded, once blanketed these plateaus. Physically stable but biogeochemically dynamic, cangas armor the landscape by pervasive and recurrent iron cycling and cementation, slowing down the delivery of weathered BIF or friable hematite–magnetite ore to erosion. We combine (U‐Th)/He dating and cosmogenic 3He measurements in supergene iron oxides to study relic banded iron‐formation (BIF) landscapesWe confirm that cangas are long‐lasting features that armor the landscape and slow the delivery of weathered BIF to erosionPrecipitation of goethite cements takes place primarily in the subsurface

Following K‐Ar dating of a mudstone and a sandstone, a third sample has been dated by the Curiosity rover exploring Gale Crater. The Mojave 2 mudstone, which contains relatively abundant jarosite, yielded a young K‐Ar bulk age of 2.57 ± 0.39 Ga (1σprecision). A two‐step heating experiment was implemented in an effort to resolve the K‐Ar ages of primary and secondary mineralogical components within the sample. This technique involves measurement of 40Ar released in low‐temperature (500°C) and high‐temperature (930°C) steps, and a model of the potassium distribution within the mineralogical components of the sample. Using this method, the high‐temperature step yields a K‐Ar model age of 4.07 ± 0.63 Ga associated with detrital plagioclase, compatible with the age obtained on the Cumberland mudstone by Curiosity. The low‐temperature step, associated with jarosite mixed with K‐bearing evaporites and/or phyllosilicates, gave a youthful K‐Ar model age of 2.12 ± 0.36 Ga. The interpretation of this result is complicated by the potential for argon loss after mineral formation. Comparison with the results on Cumberland and previously published constraints on argon retentivity of the individual phases likely to be present suggests that the formation age of the secondary materials, correcting for plausible extents of argon loss, is still less than 3 Ga, suggesting post‐3 Ga aqueous processes occurred in the sediments in Gale Crater. Such a result is inconsistent with K‐bearing mineral formation in Gale Lake and instead suggests postdepositional fluid flow at a time after surface fluvial activity on Mars is thought to have largely ceased. A third radiometric age dating experiment has been conducted on MarsThe model formation age of plagioclase is greater than 4 Ga, while the model age for jarosite is less than 3 GaThe young jarosite age suggests the presence of liquid water in Gale Crater during the Amazonian period, most likely in the subsurface

The first samples collected by the Mars 2020 mission represent units exposed on the Jezero Crater floor, from the potentially oldest Séítah formation outcrops to the potentially youngest rocks of the heavily cratered Máaz formation. Surface investigations reveal landscape‐to‐microscopic textural, mineralogical, and geochemical evidence for igneous lithologies, some possibly emplaced as lava flows. The samples contain major rock‐forming minerals such as pyroxene, olivine, and feldspar, accessory minerals including oxides and phosphates, and evidence for various degrees of aqueous activity in the form of water‐soluble salt, carbonate, sulfate, iron oxide, and iron silicate minerals. Following sample return, the compositions and ages of these variably altered igneous rocks are expected to reveal the geophysical and geochemical nature of the planet's interior at the time of emplacement, characterize martian magmatism, and place timing constraints on geologic processes, both in Jezero Crater and more widely on Mars. Petrographic observations and geochemical analyses, coupled with geochronology of secondary minerals, can also reveal the timing of aqueous activity as well as constrain the chemical and physical conditions of the environments in which these minerals precipitated, and the nature and composition of organic compounds preserved in association with these phases. Returned samples from these units will help constrain the crater chronology of Mars and the global evolution of the planet's interior, for understanding the processes that formed Jezero Crater floor units, and for constraining the style and duration of aqueous activity in Jezero Crater, past habitability, and cycling of organic elements in Jezero Crater. Here we provide a narrative of sample collection and associated in situ rover observations for the rocks collected by the Perseverance rover to provide a preliminary description of the first samples of the Mars 2020 mission. These rocks collected in Jezero Crater represent the first samples from Mars with a known geologic context, the first collected with the potential to be returned to Earth for laboratory analysis, and the first cores from rock outcrops on another planet. Remote and proximal analyses indicate that all crater floor outcrops investigated are igneous in origin. Laboratory analyses of these rocks will be useful to study the planet's interior at the time of emplacement, characterize martian magmatism, and place timing constraints on geologic processes, both in Jezero Crater and more widely on Mars. All collected rocks have interacted with water and contain secondary geochemical and mineralogical evidence that can be used to understand aqueous environments in the crater and the potential conditions of habitability for ancient life on Mars. Nine samples, consisting of four pairs of rock cores and a tube of atmospheric gas, were collected from the floor of Jezero Crater, MarsIn situ observations of crater floor outcrops, used as proxies for the samples, reveal aqueously altered igneous lithologiesPerseverance will leave one sample from each pair at the Three Forks depot and retain a second to be cached with future samples Nine samples, consisting of four pairs of rock cores and a tube of atmospheric gas, were collected from the floor of Jezero Crater, Mars In situ observations of crater floor outcrops, used as proxies for the samples, reveal aqueously altered igneous lithologies Perseverance will leave one sample from each pair at the Three Forks depot and retain a second to be cached with future samples

Variability in the sulfur isotopic composition in sediments can reflect atmospheric, geologic and biological processes. Evidence for ancient fluvio-lacustrine environments at Gale crater on Mars and a lack of efficient crustal recycling mechanisms on the planet suggests a surface environment that was once warm enough to allow the presence of liquid water, at least for discrete periods of time, and implies a greenhouse effect that may have been influenced by sulfur-bearing volcanic gases. Here we report in situ analyses of the sulfur isotopic compositions of SO2volatilized from ten sediment samples acquired by NASA’s Curiosity rover along a 13 km traverse of Gale crater. We find large variations in sulfur isotopic composition that exceed those measured for Martian meteorites and show both depletion and enrichment in 34S. Measured values of δ34S range from −47 ± 14‰ to 28 ± 7‰, similar to the range typical of terrestrial environments. Although limited geochronological constraints on the stratigraphy traversed by Curiosity are available, we propose that the observed sulfur isotopic signatures at Gale crater can be explained by equilibrium fractionation between sulfate and sulfide in an impact-driven hydrothermal system and atmospheric processing of sulfur-bearing gases during transient warm periods.

What allows a planet to be both within a potentially habitable zone and sustain habitability over long geologic time? With the advent of exoplanetary astronomy and the ongoing discovery of terrestrial‐type planets around other stars, our own solar system becomes a key testing ground for ideas about what factors control planetary evolution. Mars provides the solar system's longest record of the interplay of the physical and chemical processes relevant to habitability on an accessible rocky planet with an atmosphere and hydrosphere. Here we review current understanding and update the timeline of key processes in early Mars history. We then draw on knowledge of exoplanets and the other solar system terrestrial planets to identify six broad questions of high importance to the development and sustaining of habitability (unprioritized): (1) Is small planetary size fatal? (2) How do magnetic fields influence atmospheric evolution? (3) To what extent does starting composition dictate subsequent evolution, including redox processes and the availability of water and organics? (4) Does early impact bombardment have a net deleterious or beneficial influence? (5) How do planetary climates respond to stellar evolution, e.g., sustaining early liquid water in spite of a faint young Sun? (6) How important are the timescales of climate forcing and their dynamical drivers? Finally, we suggest crucial types of Mars measurements (unprioritized) to address these questions: (1) in situ petrology at multiple units/sites; (2) continued quantification of volatile reservoirs and new isotopic measurements of H, C, N, O, S, Cl, and noble gases in rocks that sample multiple stratigraphic sections; (3) radiometric age dating of units in stratigraphic sections and from key volcanic and impact units; (4) higher‐resolution measurements of heat flux, subsurface structure, and magnetic field anomalies coupled with absolute age dating. Understanding the evolution of early Mars will feed forward to understanding the factors driving the divergent evolutionary paths of the Earth, Venus, and thousands of small rocky extrasolar planets yet to be discovered. As more rocky planets are found around other stars, a key question is which factors are most important to understanding whether they are habitable? Within our solar system Mars preserves the longest record of the history of terrestrial planets, even longer than Earth. Exploration of Mars' rock record provides to the ability to understand why its environment ‐‐ its habitability ‐‐ changed so profoundly, going from a watery world, to the cold, dry world of today. In this paper, we review what is known of Mars history after several decades of exploration. We then list 6 key questions for understanding terrestrial planets generally and what makes them Earth‐like, Mars‐like, Venus‐like or otherwise have different fates. We then make recommendations of measurements needed in our own solar system, on Mars, to better understand how Earth‐like worlds change over time, keeping the ability to sustain life (or not) over time. Understanding the solar system terrestrial planets is crucial for interpretation of the history and habitability of rocky exoplanetsMars' accessible geologic record extends back past 4 Ga and possibly to as long ago as 5 Myr after solar system formationMars is key for testing theories of planetary evolution and processes that sustain habitability (or not) on rocky planets with atmospheres

K‐Ar and noble gas surface exposure age measurements were carried out on the Windjana sandstone, Kimberley region, Gale Crater, Mars, by using the Sample Analysis at Mars instrument on the Curiosity rover. The sandstone is unusually rich in sanidine, as determined by CheMin X‐ray diffraction, contributing to the high K2O concentration of 3.09 ± 0.20 wt % measured by Alpha‐Particle X‐ray Spectrometer analysis. A sandstone aliquot heated to ~915°C yielded a K‐Ar age of 627 ± 50 Ma. Reheating this aliquot yielded no additional Ar. A second aliquot heated in the same way yielded a much higher K‐Ar age of 1710 ± 110 Ma. These data suggest incomplete Ar extraction from a rock with a K‐Ar age older than 1710 Ma. Incomplete extraction at ~900°C is not surprising for a rock with a large fraction of K carried by Ar‐retentive K‐feldspar. Likely, variability in the exact temperature achieved by the sample from run to run, uncertainties in sample mass estimation, and possible mineral fractionation during transport and storage prior to analysis may contribute to these discrepant data. Cosmic ray exposure ages from 3He and 21Ne in the two aliquots are minimum values given the possibility of incomplete extraction. However, the general similarity between the 3He (57 ± 49 and 18 ± 32 Ma, mean 30 Ma) and 21Ne (2 ± 32 and 83 ± 24 Ma, mean 54 Ma) exposure ages provides no evidence for underextraction. The implied erosion rate at the Kimberley location is similar to that reported at the nearby Yellowknife Bay outcrop. Second in situ dating on Mars using SAM in MSLK‐Ar age discrepantCosmogenic isotope ages young and internally compatible

After prolonged mechanical ventilation patients may experience the ‘post intensive care syndrome’ (PICS) and may be candidates for post-discharge follow-up clinics. We aimed to ascertain the incidence and severity of PICS symptoms in patients surviving prolonged mechanical ventilation and to describe their views regarding follow-up clinics. In a teaching hospital, we conducted a cohort study of all adult patients discharged alive after ventilation in ICU for ≥7 days during 2013. We administered the EuroQol-5D (EQ-5D) and Hospital Anxiety and Depression Scale (HADS) via telephone interview and asked patients their views about the possible utility of a follow-up clinic. We studied 48 patients. At follow-up (average 19.5 months), seven (15%) patients had died and 14 (29%) did not participate (eight declined; two were non–English speakers; four were non-contactable). Among the 27 responders, 16 (59%) reported at least moderate problems in ≥1 EQ-5D dimension; 10 (37%) in ≥2 dimensions, and 8 (30%) in ≥3 dimensions. Moreover, 10 (37%) patients reported marked psychological symptoms; six (22%) scored borderline or abnormal on the HADS for both anxiety and depression; and four (15%) scored borderline or abnormal for one component. Finally, 21/26 (81%) patients stated that an ICU follow-up clinic would have been beneficial. At long–term follow-up, the majority of survivors of prolonged mechanical ventilation reported impaired quality of life and significant psychological symptoms. Most believed that a follow-up clinic would have been beneficial.

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The 1H and 13C nmr spectral assignments of 7bRN24,5,8,8atetrahydro7methyl4oxocyclopropacpyrrolo3,2eindol21Hylcarbonyl1Hindol5yl2benzofurancarboxamide Adozelesin 1 are described. Complete and unambiguous assignments of the hydrogen and carbon spectra were made using a combination of conventional homonuclear and gradientselected inversedetected heteronuclear nmr experiments: double quantum filtered 1H1H correlation spectroscopy COSY, gradientselected heteronuclear single quantum coherence spectroscopy gsHSQC, and gradientselected heteronuclear multiple bond coherence spectroscopy gsHMBC. The enhanced sensitivity of these experiments allowed a smaller sample concentration and shorter spectral collection times for a full nmr analysis of this compound. The nmr data corroborates the published structure of this compound.

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Bovine somatotropin was studied with respect to thermal stability, quantitative thermal denaturation kinetics, and refolding potential following thermal denaturation using a panel of 6 monoclonal antibodies and the Conformation-Sensitive Immunoassay (CSI). The antibody panel consisted of 4 conformation-dependent and 2 sequence-specific antibodies. Each of the antibodies revealed unique thermal stability profiles for their respective epitopes suggesting that they each recognize different antigenic determinants. Comparing the thermal stability profiles generated with these antibodies allowed the stability of bovine somatotropin to be "dissected" based on individual structural features. The degree to which bovine somatotropin is stabilized by disulfide bonds was examined using CSI-based quantitative thermal denaturation kinetics profiles generated under reducing and nonreducing conditions. All of the conformational epitopes unfolded faster under reducing conditions indicating that the two disulfide bonds within the somatotropin molecule impart some degree of global stabilization. The ability of bovine somatotropin to refold after reducing or nonreducing thermal denaturation was also examined using the antibody panel and the CSI. The results show that, although significant refolding was evident for some epitopes, bovine somatotropin cannot refold to the native state following thermal denaturation under either reducing or nonreducing conditions.

Helium, Sr, and Nd isotopic ratios and major and trace element compositions have been measured on a suite of lavas from the intra-plate volcanos of the Juan Fernandez Archipelago, Chile. Lavas from the islands of Mas Afuera and Mas a Tierra and from Monte Alpha and Friday seamounts have Sr and Nd isotopic ratios lying on the low143Nd/144Nd side of the mantle array (87Sr/86Sr:0.7034–0.7037;143Nd/144Nd:0.51281–0.51289). The homogeneity of these tracers suggests the involvement of a restricted range of mantle source compositions throughout Juan Fernandez volcanism. In marked contrast is the large range in3He/4He, from 7.8 to 18.0 RA. A bimodal3He/4He distribution on Mas a Tierra is associated with two distinct volcanic lineages;3He/4He ratios of 14.5–18.0 RA (n=15) occur in alkalic and tholeiitic shield basalts, whereas post-shield basanites range from 11.2 to 13.6 RA (n=12). Elemental and isotopic systematics demonstrate a transition from an enriched (Loihi-like) plume source in the shield lavas to a more MORB-like source in the post-shield volcanics. The transition between these sources is much more pronounced in3He/4He than in the other isotopic tracers. The predominantly tholeiitic basalts of Mas Afuera have exceptionally uniform isotopic and elemental characteristics; Sr and Nd ratios are similar to those of Mas a Tierra, but3He/4He ratios are lower and more uniform at 8.3±0.5 RA (n=17). The dramatic distinction between Mas Afuera and Mas a Tierra helium is surprising given the great similarity between the two islands in other geochemical characteristics. Both the Mas Afuera and Mas a Tierra results demonstrate that helium records systematic processes not readily apparent from other isotopic or elemental indicators. Neither magma chamber degassing nor local metasomatic events are likely to be responsible. We suggest that the observed variations may be attributed to mixing of plume and asthenospheric sources in which the plume component is characterized by a heterogeneous distribution of volatiles or has suffered extraction of small degree partial melts prior to mixing.

DISCUSSION The Limehouse Link tunnel Introducers Proc. Instn Civ. Engrs Tramp., 1996,117, Feb., 70 R. S. Blyth, D. W. Scott, P.T . McCreight, K. R. Farley, P. R. Glass, P. Back and M. C. Stevenson Reporter Transport Board Transport Planning and Road Panel G . Parkhouse were unlikely to be realized in practice. The objective was the total removal the tempoof rary propping. This was achieved through a programme of monitoring, instrumentation and observations at the start each tunnel front...

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