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1. Influence of Aryl Substituents on the Alignment of Ligands in the Dirhodium Tetrakis(1,2,2‐Triarylcyclopropane‐ carboxylate) Catalysts

   https://doi.org/10.1002/cctc.202001206  

   Ren, Zhi; Musaev, Djamaladdin_G; Davies, Huw_M_L (September 2020, ChemCatChem)

   Abstract Computational studies revealed that dirhodium tetrakis(1,2,2‐triarylcyclopropanecarboxylate) (Rh₂(TPCP)₄) catalysts adopt distinctive high symmetry orientations, which are dependent on the nature of the aryl substitution pattern. The parent catalyst, Rh₂(TPCP)₄, and those with ap‐substituent at the C1 aryl, such as Rh₂(p‐BrTPCP)₄and Rh₂(p‐PhTPCP)₄, adopt aC₂‐symmetric structure. Rh₂(3,5‐di(p‐^tBuC₆H₄)TPCP)₄, 3,5‐disubstituted at the C1 aryl, adopts aD₂‐symmetric structure, whereas catalysts with ano‐substituent at the C1 aryl, such as Rh₂(o‐Cl‐5‐BrTPCP)_4,adopt aC₄‐symmetric structure. 

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2. Resolving the contrasting leaf hydraulic adaptation of C₃ and C₄ grasses

   https://doi.org/10.1111/nph.20341  

   Baird, Alec_S; Taylor, Samuel_H; Pasquet‐Kok, Jessica; Vuong, Christine; Zhang, Yu; Watcharamongkol, Teera; Cochard, Hervé; Scoffoni, Christine; Edwards, Erika_J; Osborne, Colin_P; et al (January 2025, New Phytologist)

   Summary Grasses are exceptionally productive, yet their hydraulic adaptation is paradoxical. Among C₃grasses, a high photosynthetic rate (A_area) may depend on higher vein density (D_v) and hydraulic conductance (K_leaf). However, the higherD_vof C₄grasses suggests a hydraulic surplus, given their reduced need for highK_leafresulting from lower stomatal conductance (g_s).Combining hydraulic and photosynthetic physiological data for diverse common garden C₃and C₄species with data for 332 species from the published literature, and mechanistic modeling, we validated a framework for linkages of photosynthesis with hydraulic transport, anatomy, and adaptation to aridity.C₃and C₄grasses had similarK_leafin our common garden, but C₄grasses had higherK_leafthan C₃species in our meta‐analysis. Variation inK_leafdepended on outside‐xylem pathways. C₄grasses have highK_leaf : g_s, which modeling shows is essential to achieve their photosynthetic advantage.Across C₃grasses, higherA_areawas associated with higherK_leaf, and adaptation to aridity, whereas for C₄species, adaptation to aridity was associated with higherK_leaf : g_s. These associations are consistent with adaptation for stress avoidance.Hydraulic traits are a critical element of evolutionary and ecological success in C₃and C₄grasses and are crucial avenues for crop design and ecological forecasting. 

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3. Reduced global plant respiration due to the acclimation of leaf dark respiration coupled with photosynthesis

   https://doi.org/10.1111/nph.19355  

   Ren, Yanghang; Wang, Han; Harrison, Sandy_P; Prentice, I_Colin; Atkin, Owen_K; Smith, Nicholas_G; Mengoli, Giulia; Stefanski, Artur; Reich, Peter_B (October 2023, New Phytologist)

   Summary Leaf dark respiration (R_d) acclimates to environmental changes. However, the magnitude, controls and time scales of acclimation remain unclear and are inconsistently treated in ecosystem models.We hypothesized thatR_dand Rubisco carboxylation capacity (V_cmax) at 25°C (R_d,25,V_cmax,25) are coordinated so thatR_d,25variations supportV_cmax,25at a level allowing full light use, withV_cmax,25reflecting daytime conditions (for photosynthesis), andR_d,25/V_cmax,25reflecting night‐time conditions (for starch degradation and sucrose export). We tested this hypothesis temporally using a 5‐yr warming experiment, and spatially using an extensive field‐measurement data set. We compared the results to three published alternatives:R_d,25declines linearly with daily average prior temperature;R_dat average prior night temperatures tends towards a constant value; andR_d,25/V_cmax,25is constant.Our hypothesis accounted for more variation in observedR_d,25over time (R² = 0.74) and space (R² = 0.68) than the alternatives. Night‐time temperature dominated the seasonal time‐course ofR_d, with an apparent response time scale ofc.2 wk.V_cmaxdominated the spatial patterns.Our acclimation hypothesis results in a smaller increase in globalR_din response to rising CO₂and warming than is projected by the two of three alternative hypotheses, and by current models. 

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4. Constraining the H ₂ column densities in the diffuse interstellar medium using dust extinction and H I data

   https://doi.org/10.1051/0004-6361/202347968  

   Skalidis, R; Goldsmith, P F; Hopkins, P F; Ponnada, S B (February 2024, Astronomy & Astrophysics)

   Context. Carbon monoxide (CO) is a poor tracer of H₂in the diffuse interstellar medium (ISM), where most of the carbon is not incorporated into CO molecules, unlike the situation at higher extinctions. Aims. We present a novel, indirect method for constraining H₂column densities (N_H2) without employing CO observations. We show that previously recognized nonlinearities in the relation between the extinction,A_V(H₂), derived from dust emission and the H Icolumn density (N_H I) are due to the presence of molecular gas. Methods. We employed archival (N_H2) data, obtained from the UV spectra of stars, and calculatedA_V(H₂) toward these sight lines using 3D extinction maps. The following relation fits the data: logN_H2= 1.38742 (logA_V(H₂)⁾³− 0.05359 (logA_V(H₂)⁾²+ 0.25722 logA_V(H₂) + 20.67191. This relation is useful for constrainingN_H2in the diffuse ISM as it requires onlyN_H Iand dust extinction data, which are both easily accessible. In 95% of the cases, the estimates produced by the fitted equation have deviations of less than a factor of 3.5. We constructed aN_H2map of our Galaxy and compared it to the CO integrated intensity (W_CO) distribution. Results. We find that the average ratio (X_CO) betweenN_H2andW_COis approximately equal to 2 × 10²⁰cm⁻²(K km s⁻¹)⁻¹, consistent with previous estimates. However, we find that theX_COfactor varies by orders of magnitude on arcminute scales between the outer and the central portions of molecular clouds. For regions withN_H2≳ 10²⁰cm⁻², we estimate that the average H₂fractional abundance,f_H2= 2N_H2/(2N_H2+N_H I), is 0.25. Multiple (distinct) largely atomic clouds are likely found along high-extinction sightlines (A_V≥ 1 mag), hence limitingf_H2in these directions. Conclusions. More than 50% of the lines of sight withN_H2≥ 10²⁰cm⁻²are untraceable by CO with aJ= 1−0 sensitivity limitW_CO= 1 K km s⁻¹. 

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5. On the complexity of bidirected interleaved Dyck-reachability

   https://doi.org/10.1145/3434340  

   Li, Yuanbo; Zhang, Qirun; Reps, Thomas (January 2021, Proceedings of the ACM on Programming Languages)

   Many program analyses need to reason about pairs of matching actions, such as call/return, lock/unlock, or set-field/get-field. The family of Dyck languages {D_k}, whereD_khaskkinds of parenthesis pairs, can be used to model matching actions as balanced parentheses. Consequently, many program-analysis problems can be formulated as Dyck-reachability problems on edge-labeled digraphs.Interleaved Dyck-reachability(InterDyck-reachability), denoted byD_k⊙D_k-reachability, is a natural extension of Dyck-reachability that allows one to formulate program-analysis problems that involvemultiplekinds of matching-action pairs. Unfortunately, the general InterDyck-reachability problem is undecidable. In this paper, we study variants of InterDyck-reachability onbidirected graphs, where for each edge ⟨p,q⟩ labeled by an open parenthesis ”(_a”, there is an edge ⟨q,p⟩ labeled by the corresponding close parenthesis ”)_a”, andvice versa. Language-reachability on a bidirected graph has proven to be useful both (1) in its own right, as a way to formalize many program-analysis problems, such as pointer analysis, and (2) as arelaxationmethod that uses a fast algorithm to over-approximate language-reachability on a directed graph. However, unlike its directed counterpart, the complexity of bidirected InterDyck-reachability still remains open. We establish the first decidable variant (i.e.,D₁⊙D₁-reachability) of bidirected InterDyck-reachability. InD₁⊙D₁-reachability, each of the two Dyck languages is restricted to have only a single kind of parenthesis pair. In particular, we show that the bidirectedD₁⊙D₁problem is in PTIME. We also show that when one extends each Dyck language to involvekdifferent kinds of parentheses (i.e.,D_k⊙D_k-reachability withk≥ 2), the problem is NP-hard (and therefore much harder). We have implemented the polynomial-time algorithm for bidirectedD₁⊙D₁-reachability.D_k⊙D_k-reachability provides a new over-approximation method for bidirectedD_k⊙D_k-reachability in the sense thatD_k⊙D_k-reachability can first be relaxed to bidirectedD₁⊙D₁-reachability, and then the resulting bidirectedD₁⊙D₁-reachability problem is solved precisely. We compare thisD₁⊙D₁-reachability-based approach against another known over-approximatingD_k⊙D_k-reachability algorithm. Surprisingly, we found that the over-approximation approach based on bidirectedD₁⊙D₁-reachability computesmore precisesolutions, even though theD₁⊙D₁formalism is inherently less expressive than theD_k⊙D_kformalism. 

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