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What is a cross-coupling? An argument for a universal definition
No full textDespite amazing advances in cross-coupling technologies over the past several decades, there is not a consistent definition of what a cross-coupling reaction is. Often, definitions rely on comparison to “traditional” palladium-catalyzed cross-couplings pioneered in the 1970s by chemists such as Suzuki, Negishi, and Heck. While these reactions provide a basis for a cross-coupling definition, they do not define this type of transformation, originally described by Linstead almost 20 years prior. Rather than modify and compartmentalize modern transformations to categorize them into either a synthetic or mechanistic definition, we make an argument for broadening the cross-coupling definition to the union of two distinct molecular entities in a covalent-bond-forming process, to encourage discussion around exploring novel reactivity and disconnections. In addition to making a case for a universal cross-coupling definition, we cite specific examples of reactions that break the mold of prior cross-coupling definitions. We believe this perspective will stimulate dialog around what it means to be a cross-coupling and in turn inspire future developments within this field
Fully-coupled thermal-electric modeling of thermoelectric generators
No full textNumerical models of thermoelectric generators require quantification of discretization uncertainty, the scrutinization of thermoelectric phenomena on model energy imbalances and simultaneous thermal–electric predictions, and the rectification of disagreement with analytic models when considering temperature-dependent material properties. Within this methods paper, two fully coupled, thermal–electric unicouple-level models are developed and evaluated over various thermal and electrical conditions to address the aforementioned issues—a numeric model in ANSYS CFX and an iterative analytic model. Model results were compared to ANSYS Thermal–Electric (TE) and ANSYS Fluent. Agreement between all models’ electrical and thermal predictions was achieved, albeit ANSYS Fluent’s thermal predictions exhibited high percent differences (7–8%) and had global energy imbalances on the order of 15% due to incongruent thermal–electrical power output predictions. ANSYS TE congruently predicts power output when considering the device’s thermal behavior and electrical performance separately, with disagreement on the order of a percent. Through incorporating all thermoelectric phenomena, ANSYS CFX’s global energy imbalances were hundredths to thousandths of a percent; exclusion of pertinent thermoelectric phenomena such as Thomson and Bridgman heating caused imbalances of tens of percent. The inclusion of Thomson heat is imperative when modeling thermoelectric devices. The analytic model’s thermal and electrical performance predictions are within ANSYS CFX’s uncertainty (2–5%), and these predictions yielded percent difference of less than 1% in comparison to ANSYS CFX when the unicouple produces ±50% maximum power. By using temperature-integrated averages of material properties, analytic modeling is sufficient for the thermal–electric characterization of unicouples with interconnectors operating under Dirichlet thermal boundary conditions
Cold mode gas accretion on two galaxy groups at z ∼ 2
No full textWe present Keck Cosmic Web Imager (KCWI) integral field spectroscopy (IFS) observations of rest-frame UV emission lines Lyα, CIVλλ 1548 Å, 1550Å, and HeII 1640 Å observed in the circumgalactic medium (CGM) of two z = 2 radio-loud quasar host galaxies. We detect extended emission on 80–90 kpc scale in Lyα in both systems with CIV and HeII emission also detected out to 30–50 kpc. All emission lines show kinematics with a blue and redshifted gradient pattern consistent with velocities seen in massive dark matter haloes and similar to kinematic patterns of inflowing gas seen in hydrodynamical simulations. Using the kinematics of both resolved Lyα emission and absorption, we can confirm that both kinematic structures are associated with accretion. Combining the KCWI data with molecular gas observations with Atacama Large Millimeter/submillimeter Array (ALMA) and high-spatial resolution of ionized gas with Keck OSIRIS, we find that both quasar host galaxies reside in proto-group environments at z = 2. We estimate 1–6 × 10¹⁰ M_⊙ of warm-ionized gas within 30–50 kpc from the quasar that is likely accreting on to the galaxy group. We estimate inflow rates of 60–200 M_⊙ yr⁻¹, within an order of magnitude of the outflow rates in these systems. In the 4C 09.17 system, we detect narrow gas streams associated with satellite galaxies, potentially reminiscent of ram-pressure stripping seen in local galaxy groups and clusters. We find that the quasar host galaxies reside in dynamically complex environments, with ongoing mergers, gas accretion, ISM stripping, and outflows likely playing an important role in shaping the assembly and evolution of massive galaxies at cosmic noon
Deep Synoptic Array science: a 50 Mpc fast radio burst constrains the mass of the Milky Way circumgalactic medium
No full textWe present the Deep Synoptic Array (DSA-110) discovery and interferometric localization of the so far non-repeating FRB 20220319D. The FRB originates in a young, rapidly star-forming barred spiral galaxy, IRAS 02044+7048, at just 50 Mpc. Although the NE2001 and YMW16 models for the Galactic interstellar-medium (ISM) contribution to the DM of FRB 20220319D exceed its total observed DM, we show that uncertainties in these models accommodate an extragalactic origin for the burst. We derive a conservative upper limit on the DM contributed by the circumgalactic medium (CGM) of the Milky Way: the limit is either 28.7 pc cm⁻³ and 47.3 pc cm⁻³, depending on which of two pulsars nearby on the sky to FRB 20220319D is used to estimate the ISM DM. These limits both imply that the total Galactic CGM mass is <10¹¹ M_⊙, and that the baryonic mass of the Milky Way is ≲60% of the cosmological average given the total halo mass. More stringent albeit less conservative constraints are possible when the DMs of pulsars in the distant globular cluster M53 are additionally considered. Although our constraints are sensitive to possible anisotropy in the CGM and to the assumed form of the radial-density profile, they are not subject to uncertainties in the chemical and thermal properties of the CGM. Our results strongly support scenarios commonly predicted by galaxy-formation simulations wherein feedback processes expel baryonic matter from the halos of galaxies like the Milky Way
A 100-Gb/s PAM4 Optical Transmitter in a 3-D-Integrated SiPh-CMOS Platform Using Segmented MOSCAP Modulators
No full textThis article presents a 100-Gb/s four-level pulse-amplitude modulation (PAM4) optical transmitter system implemented in a 3-D-integrated silicon photonics-CMOS platform. The photonics chip includes a push–pull segmented Mach–Zehnder modulator (MZM) structure using highly capacitive (415 fF–1.1 pF), yet optically efficient ( V_πL=0.8V⋅ cm) metal–oxide–silicon capacitor (MOSCAP) phase modulators. Two pairs of U-shaped modulator segments with effective lengths of 170 and 450 μm are driven at 50 GBd by a dual-channel 28-nm CMOS driver, which is flip-chip bonded to the photonics chip. The driver cores utilize digitally controllable pre-distortion (PD) and inductive peaking to achieve sufficient electro-optical bandwidth (EOBW). The drivers deliver 1.2-Vppd swing to modulators using a 0.9-V supply and on-chip serializers that generate 50-Gb/s data streams. The electronics chip consumes 240 mW achieving 2.4-pJ/bit energy efficiency. The overall EOBW, without any PD, is increased by approximately 56% and 48% for the 170- and 450- μm segments, respectively, when compared to their EOBW measured by 65-GHz 50-Ω terminated probes. The optical input power to the photonics chip is +10 dBm, and an erbium-doped fiber amplifier amplifies output signals by 11 dB. The 50-Gb/s nonreturn to zero (NRZ) optical raw eye diagram exhibits 4.3-dB extinction ratio (ER) and 1.2 dBm of optical modulation amplitude (OMA). The 100-Gb/s PAM4 optical raw eye diagram shows 4.3-dB ER and 1.4-dBm OMA with a transmitter dispersion eye closure quaternary (TDECQ) of 1.53 dB after a five-tap feed-forward-equalization (FFE) filter. The PAM4 TDECQ changes by 53% when the temperature is increased from 30 °C to 90 °C at the optimum forward bias voltage of 1 V
The magmatic web beneath Hawai‘i
No full textThe deep magmatic architecture of the Hawaiian volcanic system is central to understanding the transport of magma from the upper mantle to the individual volcanoes. We leverage advances in earthquake monitoring with deep learning algorithms to image the structures underlying a major mantle earthquake swarm of nearly 200,000 events that rapidly accelerated after the 2018 Kīlauea caldera collapse. At depths of 36 to 43 kilometers, we resolve a 15-kilometers-long collection of near-horizontal sheeted structures that we identify as a sill complex. These sills connect to the lower depths of Kīlauea’s plumbing by a 25-kilometers-long belt of seismicity. Additionally, a column of seismicity links the sill complex to a shallow décollement near Mauna Loa. These findings implicate the mantle sill complex as a nexus for magma transport beneath Hawai‘i and furthermore indicate widespread magmatic connectivity in the volcanic system
A highly anisotropic polymorph
No full textSuperconductivity with an anisotropy is revealed in a layered material. This result points towards a version of superconductivity where spin–orbit interactions produce a material that is resilient to external magnetic fields
An approximate line attractor in the hypothalamus encodes an aggressive state
No full textThe hypothalamus regulates innate social behaviors, including mating and aggression. These behaviors can be evoked by optogenetic stimulation of specific neuronal subpopulations within MPOA and VMHvl, respectively. Here, we perform dynamical systems modeling of population neuronal activity in these nuclei during social behaviors. In VMHvl, unsupervised analysis identified a dominant dimension of neural activity with a large time constant (>50 s), generating an approximate line attractor in neural state space. Progression of the neural trajectory along this attractor was correlated with an escalation of agonistic behavior, suggesting that it may encode a scalable state of aggressiveness. Consistent with this, individual differences in the magnitude of the integration dimension time constant were strongly correlated with differences in aggressiveness. In contrast, approximate line attractors were not observed in MPOA during mating; instead, neurons with fast dynamics were tuned to specific actions. Thus, different hypothalamic nuclei employ distinct neural population codes to represent similar social behaviors
Modeling compact binary merger waveforms beyond general relativity
No full textThe parametrized post-Einsteinian framework modifies inspiral waveform models to incorporate effects beyond general relativity (GR). We extend the existing model into the merger-ringdown regime. The modification introduced here adds a single degree of freedom that corresponds to a change in the binary coalescence time. Other merger properties remain as predicted by GR. We discuss parameter estimation with this model, and how it can be used to extract information from beyond-GR waveforms
The Gross-Neveu-Yukawa archipelago
No full textWe perform a bootstrap analysis of a mixed system of four-point functions of bosonic and fermionic operators in parity-preserving 3d CFTs with O(N) global symmetry. Our results provide rigorous bounds on the scaling dimensions of the O(N)-symmetric Gross-Neveu-Yukawa (GNY) fixed points, constraining these theories to live in isolated islands in the space of CFT data. We focus on the cases N = 1, 2, 4, 8, which have applications to phase transitions in condensed matter systems, and compare our bounds to previous analytical and numerical results