Inspecting the Running Process of Horizontal Federated Learning via Visual Analytics.

As a decentralized training approach, horizontal federated learning (HFL) enables distributed clients to collaboratively learn a machine learning model while keeping personal/private information on local devices. Despite the enhanced performance and efficiency of HFL over local training, clues for inspecting the behaviors of the participating clients and the federated model are usually lacking due to the privacy-preserving nature of HFL. Consequently, the users can only conduct a shallow-level analysis of potential abnormal behaviors and have limited means to assess the contributions of individual clients and implement the necessary intervention. Visualization techniques have been introduced to facilitate the HFL process inspection, usually by providing model metrics and evaluation results as a dashboard representation. Although the existing visualization methods allow a simple examination of the HFL model performance, they cannot support the intensive exploration of the HFL process. In this article, strictly following the HFL privacy-preserving protocol, we design an exploratory visual analytics system for the HFL process termed HFLens, which supports comparative visual interpretation at the overview, communication round, and client instance levels. Specifically, the proposed system facilitates the investigation of the overall process involving all clients, the correlation analysis of clients' information in one or different communication round(s), the identification of potential anomalies, and the contribution assessment of each HFL client. Two case studies confirm the efficacy of our system. Experts' feedback suggests that our approach indeed helps in understanding and diagnosing the HFL process better.

Gear Shifting of Quadriceps during Isometric Knee Extension Disclosed Using Ultrasonography.

Ultrasonography has been widely employed to estimate the morphological changes of muscle during contraction. To further investigate the motion pattern of quadriceps during isometric knee extensions, we studied the relative motion pattern between femur and quadriceps under ultrasonography. An interesting observation is that although the force of isometric knee extension can be controlled to change almost linearly, femur in the simultaneously captured ultrasound video sequences has several different piecewise moving patterns. This phenomenon is like quadriceps having several forward gear ratios like a car starting from rest towards maximal voluntary contraction (MVC) and then returning to rest. Therefore, to verify this assumption, we captured several ultrasound video sequences of isometric knee extension and collected the torque/force signal simultaneously. Then we extract the shapes of femur from these ultrasound video sequences using video processing techniques and study the motion pattern both qualitatively and quantitatively. The phenomenon can be seen easier via a comparison between the torque signal and relative spatial distance between femur and quadriceps. Furthermore, we use cluster analysis techniques to study the process and the clustering results also provided preliminary support to the conclusion that, during both ramp increasing and decreasing phases, quadriceps contraction may have several forward gear ratios relative to femur.

Novel Consensus Gene Selection Criteria for Distributed GPU Partial Least Squares-Based Gene Microarray Analysis in Diffused Large B Cell Lymphoma (DLBCL) and Related Findings.

This paper proposes a novel consensus gene selection criteria for partial least squares-based gene microarray analysis. By quantifying the extent of consistency and distinctiveness of the differential gene expressions across different double cross validations (CV) or randomizations in terms of occurrence and randomization p-values, the proposed criteria are able to identify a more comprehensive genes associated with the underlying disease. A Distributed GPU implementation has been proposed to accelerate the gene selection problem and about 8-11 times speed up has been achieved based on the microarray datasets considered. Simulation results using various cancer gene microarray datasets show that the proposed approach is able to achieve highly comparable classification accuracy in comparing with many conventional approaches. Furthermore, enrichment analysis on the selected genes for Diffused Large B Cell Lymphoma (DLBCL) and Prostate Cancer datasets and show that only the proposed approach is able to identify gene lists enriched in different pathways with significant p-values. In contrast, sufficient statistical significance cannot be found for conventional SVM-RFE and the t-test. The reliability in identifying and establishing statistical significance of the gene findings makes the proposed approach an attractive alternative for cancer related researches based on gene expression profiling or other similar data.

Automatic Extraction of Central Tendon of Rectus Femoris (CT-RF) in Ultrasound Images Using a New Intensity-Compensated Free-Form Deformation-Based Tracking Algorithm With Local Shape Refinement.

Ultrasonography is an important diagnostic imaging technique for visualization of tendons, which provides useful health diagnostic and fundamental information in neuromuscular studies of human motion systems. Conventional ultrasonic-based tendon studies, however, are highly dependent on subjective experience of operators due to various impairments of ultrasound images. Dynamic changes of muscle and tendon deformation in a sequence can hardly be manually processed. Consequently, there is an urgent need for automatic analysis of tendon behavior. This paper proposes an automatic ultrasonic tendon tracking algorithm to extract the shape deformation of central tendon of rectus femoris (CT-RF) from ultrasonic image sequences. The tracking problem is complicated by the highly deformable tendon, time-varying brightness, and the inconspicuousness of the target. To address this difficult tracking problem, we proposed a new intensity-compensated free-form deformation (IC-FFD)-based tracking algorithm with local shape refinement (LSR). Experimental results and comparison show that the proposed IC-FFD-LSR algorithm outperforms IC-FFD and conventional methods such as MI-FFD in CT-RF tracking.

Molecular Catalysis of the Electrochemical and Photochemical Reduction of CO2 with Earth-Abundant Metal Complexes. Selective Production of CO vs HCOOH by Switching of the Metal Center.

Molecular catalysis of carbon dioxide reduction using earth-abundant metal complexes as catalysts is a key challenge related to the production of useful products--the "solar fuels"--in which solar energy would be stored. A direct approach using sunlight energy as well as an indirect approach where sunlight is first converted into electricity could be used. A Co(II) complex and a Fe(III) complex, both bearing the same pentadentate N5 ligand (2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene), were synthesized, and their catalytic activity toward CO2 reduction was investigated. Carbon monoxide was formed with the cobalt complex, while formic acid was obtained with the iron-based catalyst, thus showing that the catalysis product can be switched by changing the metal center. Selective CO2 reduction occurs under electrochemical conditions as well as photochemical conditions when using a photosensitizer under visible light excitation (λ > 460 nm, solvent acetonitrile) with the Co catalyst. In the case of the Fe catalyst, selective HCOOH production occurs at low overpotential. Sustained catalytic activity over long periods of time and high turnover numbers were observed in both cases. A catalytic mechanism is suggested on the basis of experimental results and preliminary quantum chemistry calculations.

Dual-Emissive Cyclometalated Iridium(III) Polypyridine Complexes as Ratiometric Biological Probes and Organelle-Selective Bioimaging Reagents.

In this Article, we present a series of cyclometalated iridium(III) polypyridine complexes of the formula [Ir(N^C)2(N^N)](PF6) that showed dual emission under ambient conditions. The structures of the cyclometalating and diimine ligands were changed systematically to investigate the effects of the substituents on the dual-emission properties of the complexes. On the basis of the photophysical data, the high-energy (HE) and low-energy (LE) emission features of the complexes were assigned to triplet intraligand ((3)IL) and triplet charge-transfer ((3)CT) excited states, respectively. Time-dependent density functional theory (TD-DFT) calculations supported these assignments and indicated that the dual emission resulted from the interruption of the communication between the higher-lying (3)IL and the lower-lying (3)CT states by a triplet amine-to-ligand charge-transfer ((3)NLCT) state. Also, the avidin-binding properties of the biotin complexes were studied by emission titrations, and the results showed that the dual-emissive complexes can be utilized as ratiometric probes for avidin. Additionally, all the complexes exhibited efficient cellular uptake by live HeLa cells. The MTT and Annexin V assays confirmed that no cell death and early apoptosis occurred during the cell imaging experiments. Interestingly, laser-scanning confocal microscopy revealed that the complexes were selectively localized on the cell membrane, mitochondria, or both, depending on the nature of the substituents of the ligands. The results of this work will contribute to the future development of dual-emissive transition metal complexes as ratiometric probes and organelle-selective bioimaging reagents.

Probing the reactivity of microhydrated α-nucleophile in the anionic gas-phase S(N)2 reaction.

To probe the kinetic performance of microsolvated α-nucleophile, the G2(+)M calculations were carried out for the gas-phase S(N)2 reactions of monohydrated and dihydrated α-oxy-nucleophiles XO(-)(H2O)(n = 1,2) (X = HO, CH3O, F, Cl, Br), and α-sulfur-nucleophile, HSS(-)(H2O)(n = 1,2), toward CH3Cl. We compared the reactivities of hydrated α-nucleophiles to those of hydrated normal nucleophiles. Our calculations show that the α-effect of monohydrated and dihydrated α-oxy-nucleophiles will become weaker than those of unhydrated ones if we apply a plot of activation barrier as a function of anion basicity. Whereas the enhanced reactivity of monohydrated and dihydrated ROO(-) (R = H, Me) could be observed if compared them with the specific normal nucleophiles, RO(-) (R = H, Me). This phenomena can not be seen in the comparisons of XO(-)(H2O)(n = 1,2) (X = F, Cl, Br) with ClC2H4O(-)(H2O)(n = 1,2), a normal nucleophile with similar gas basicity to XO(-)(H2O)(n = 1,2). These results have been carefully analyzed by natural bond orbital theory and activation strain model. Meanwhile, the relationships between activation barriers with reaction energies and the ionization energies of α-nucleophile are also discussed.

Strongly phosphorescent neutral rhenium(i) isocyanoborato complexes: synthesis, characterization, and photophysical, electrochemical, and computational studies.

A new series of neutral isocyanoborato rhenium(I) diimine complexes [Re(CO)3 (N^N)(CNBR3 )], where N^N=bpy, 4,4'-Me2 bpy, phen, 4,7-Me2 phen, 2,9-Me2 phen, 3,4,7,8-Me4 phen; R=C6 F5 , C6 H5 , Cl, 4-ClC6 H4 , 3,5-(CF3 )2 C6 H3 , with various isocyanoborate and diimine ligands of diverse electronic and steric nature have been synthesized and characterized. The X-ray crystal structures of six complexes have also been determined. These complexes displayed intense bluish green to yellow phosphorescence at room temperature in dichloromethane solution. The photophysical and electrochemical properties of these complexes had been investigated. To elucidate the electronic structures and transitions of these complexes, DFT and TD-DFT calculations have been performed, which revealed that the lowest-energy electronic transition associated with these complexes originates from a mixture of MLCT [dπ(Re)→π*(N^N)] and LLCT [π(CNBR3 )→π*(N^N)] transitions.

Catalytic water oxidation by ruthenium(II) quaterpyridine (qpy) complexes: evidence for ruthenium(III) qpy-N,N'''-dioxide as the real catalysts.

Polypyridyl and related ligands have been widely used for the development of water oxidation catalysts. Supposedly these ligands are oxidation-resistant and can stabilize high-oxidation-state intermediates. In this work a series of ruthenium(II) complexes [Ru(qpy)(L)2 ](2+) (qpy=2,2':6',2'':6'',2'''-quaterpyridine; L=substituted pyridine) have been synthesized and found to catalyze Ce(IV) -driven water oxidation, with turnover numbers of up to 2100. However, these ruthenium complexes are found to function only as precatalysts; first, they have to be oxidized to the qpy-N,N'''-dioxide (ONNO) complexes [Ru(ONNO)(L)2 ](3+) which are the real catalysts for water oxidation.

Concerted or stepwise mechanism? New insight into the water-mediated neutral hydrolysis of carbonyl sulfide.

The water-mediated neutral hydrolysis mechanism of carbonyl sulfide (OCS) has been re-examined using the hybrid supramolecule/continuum models with n = 2-8 explicit water cluster at the level of MP2(fc)(CPCM)/6-311++G(d,p)//MP2(fc)(CPCM)/6-31+G(d). Present calculations indicate that the potential energy surface in water solution is different from the one in the gas-phase, and only stepwise mechanism is observed in aqueous solution, i.e., monothiocarbonic acid (H2CO2S) is formed via monothiocarbonate (OCSOH(-), MTC) and its counterion, protonated water cluster, (H2O)nH3O(+). The predicted rate-determining step (RDS) barrier for the stepwise mechanism in water solution, about 90 kJ/mol, shows good agreement with the experimental values, 83.7-96.2 kJ/mol using six- or eight-water model including two cooperative water molecules. Moreover, two reaction pathways, the nucleophilic addition of water molecule across the C═O or the C═S bond of OCS are competitive.

G2(+)M study on N-alkylamino cation affinities of neutral main-group element hydrides: trends across the periodic table.

We have made an extensive theoretical exploration of gas-phase N-alkylamino cation affinities (NAAMCA), including amino cation affinities (AMCA) and N-dimethylamino cation affinities (NDMAMCA), of neutral main-group element hydrides of groups 15-17 and periods 2-4 in the periodic table by using the G2(+)M method. Some similarities and differences are found between NAAMCA and the corresponding alkyl cation affinities (ACA) of H(n)X. Our calculations show that the AMCA and NDMAMCA are systematically lower than the corresponding proton affinities (PA) for H(n)X. In general, there is no linear correlation between NAAMCA and PA of H(n)X. Instead, the correlations exist only within the central elements X in period 2, or periods 3-4, which is significantly different from the reasonable correlations between ACA and PA for all H(n)X. NAAMCA (H(n)X) are weaker than NAAMCA (H(n-1)X(-)) by more than 700 kJ/mol and generally stronger than ACA (H(n)X), with three exceptions: H2ONR2(+)(R = H, Me) and HFNH2(+). These new findings can be rationalized by the negative hyperconjugation and Pauli repulsion.

The α-effect exhibited in gas-phase S(N)2@N and S(N)2@C reactions.

In order to explore the existence of α-effect in gas-phase S(N)2@N reactions, and to compare its similarity and difference with its counterpart in S(N)2@C reactions, we have carried out a theoretical study on the reactivity of six α-oxy-Nus (FO(-), ClO(-), BrO(-), HOO(-), HSO(-), H2NO(-)) in the S(N)2 reactions toward NR2Cl (R = H, Me) and RCl (R = Me, i-Pr) using the G2(+)M theory. An enhanced reactivity induced by the α-atom is found in all examined systems. The magnitude of the α-effect in the reactions of NR2Cl (R = H, Me) is generally smaller than that in the corresponding S(N)2 reaction, but their variation trend with the identity of α-atom is very similar. The origin of the α-effect of the S(N)2@N reactions is discussed in terms of activation strain analysis and thermodynamic analysis, indicating that the α-effect in the S(N)2@N reactions largely arises from transition state stabilization, and the "hyper-reactivity" of these α-Nus is also accompanied by an enhanced thermodynamic stability of products from the n(N) → σ*(O-Y) negative hyperconjugation. Meanwhile, it is found that the reactivity of oxy-Nus in the S(N)2 reactions toward NMe2Cl is lower than toward i-PrCl, which is different from previous experiments, that is, the S(N)2 reactions of NH2Cl is more facile than MeCl.

Comprehensive theoretical studies on the gas phase SN2 reactions of anionic nucleophiles toward chloroamine and N-chlorodimethylamine with inversion and retention mechanisms.

The anionic S(N)2 reactions at neutral nitrogen, Nu(-) + NR(2)Cl → NR(2)Nu + Cl(-) (R = H, Me; Nu = F, Cl, Br, OH, SH, SeH, NH(2), PH(2), AsH(2)) have been systematically studied computationally at the modified G2(+) level. Two reaction mechanisms, inversion and retention of configuration, have been investigated. The main purposes of this work are to explore the reactivity trend of anions toward NR(2)Cl (R = H, Me), the steric effect on the potential energy surfaces, and the leaving ability of the anion in S(N)2@N reactions. Our calculations indicate that the complexation energies are determined by the gas basicity (GB) of the nucleophile and the electronegativity (EN) of the attacking atom, and the overall reaction barrier in the inversion pathway is basically controlled by the GB value of the nucleophile. The retention pathway in the reactions of NR(2)Cl with Nu(-) (Nu = F, Cl, Br, OH, SH, SeH) is energetically unfavorable due to the barriers being larger than those in the inversion pathway by more than 120 kJ mol(-1). Activation strain model analyses show that a higher deformation energy and a weaker interaction between deformed reactants lead to higher overall barriers in the reactions of NMe(2)Cl than those in the reactions of NH(2)Cl. Our studies on the reverse process of the title reactions suggest that the leaving ability of the anion in the gas phase anionic S(N)2@N reactions is mainly determined by the strength of the N-LG bond, which is related to the negative hyperconjugation inherent in NR(2)Nu (R = H, Me; Nu = HO, HS, HSe, NH(2), PH(2), AsH(2)).

Insight into the role of the counteranion of an imidazolium salt in organocatalysis: a combined experimental and computational study.

N-Heterocyclic carbenes (NHCs) can serve as very reactive nucleophilic catalysts and exhibit strong basicity. Herein, we initiate a combined experimental and computational investigation of the NHC-catalyzed ring-closing reactions of 4-(2-formylphenoxy)but-2-enoate derivatives 1 to uncover the relationship between the counteranion of an azolium salt, the nucleophilicity and basicity of the carbene species, and the catalytic performance of the carbene species by taking imidazolium salts IPr⋅HX (X=counteranion, IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) as the representative precatalysts. The plausible mechanisms of IPr-mediated ring-closing reactions have been investigated by using DFT calculations. The hydrogen-accepting ability, assigned as the basicity of the counteranion of IPr⋅HX and evaluated by DFT calculations, is correlated with the rate of deprotonation of C2 in IPr⋅HX, which could be monitored by the capture of the free carbene formed in situ with elemental sulfur. The deprotonation of C2 in IPr⋅HX with a more basic anion gives rise to a higher concentration of the free carbene and vice versa. At a relatively low concentration, IPr prefers to show a nucleophilic character to induce the intramolecular Stetter reaction. At a relatively high concentration, IPr primarily acts as a base to afford benzofuran derivatives. These data comprehensively disclose, for the first time, that the counteranions of azolium salts significantly influence not only the catalytic activity, but also possibly the reaction mechanism.

Cooperative effect of water molecules in the self-catalyzed neutral hydrolysis of isocyanic acid: a comprehensive theoretical study.

The detailed reaction mechanism for the water-assisted hydrolysis of isocyanic acid, HNCO + (n + 1) H(2)O → CO(2) + NH(3) + nH(2)O (n = 0-6), taking place in the gas phase, has been investigated. All structures were optimized and characterized at the MP2/6-31 + G level of theory, and then re-optimized at MP2/6-311++G. The seven explicit water molecules participating in the hydrolysis can be divided into two groups, one directly involved in the proton relay, and the other located in the vicinity of the substrate playing the cooperative role by engaging in hydrogen-bonding to HN = C = O. Two possible reaction pathways, the addition of water molecule across the C = N bond or across the C = O bond, are discussed, and the former is proved to be more favorable energetically. Our calculations suggest that, in the most kinetically favorable pathway for the titled hydrolysis, three water molecules are directly participating in the hydrogen transfer via an eight-membered cyclic transition state, while the other four water molecules catalyze the hydrolysis of HN = C = O by forming three eight-membered cooperative loops near the substrate. This strain-free hydrogen-bond network leads to the best estimated rate-determining activation energy of 24.9 kJ mol(-1) at 600 K, in excellent agreement with the gas-phase kinetic experimental result, 25.8 kJ mol(-1).

Enhanced reactivity of RC[triple bond]CZ- (R = H and Cl; Z = O, S, and Se) and the influence of leaving group on the alpha-effect in the E2 reactions.

The enhanced reactivity exhibited by six pseudo-alpha-bases, RC[triple bond]CZ(-) (R = H and Cl; Z = O, S, and Se) in gas-phase E2 reactions with ethyl chloride was examined at the G2(+) level. It is found that anomalous reactivity is observed despite the fact that these chalcogen bases do not possess adjacent lone-pair electrons. The influence of the halide leaving groups on the alpha-effect and the origin of the alpha-effect in the E2 reactions of ethyl halides are investigated and discussed.

Cooperative effect of solvent in the neutral hydration of ketenimine: an ab initio study using the hybrid cluster/continuum model.

The detailed reaction pathways for the hydration of ketenimine by water and water clusters containing up to five explicit water molecules (CH(2) =C=NH + (n + 1)H(2)O --> CH(3)CONH(2) + nH(2)O, n = 0-4) in the gas phase have been investigated by the MP2 method in conjunction with the 6-31+G* and 6-311++G** basis sets, and the effects of bulk solvent are taken into account according to the conductor-like polarizable continuum model (COSMO). In the hybrid cluster/continuum model, apart from one directly attacking water molecule, four explicit water molecules participating in the water-assisted hydrolysis of ketenimine are divided into two groups, one involving in the proton relay and the other near the nonreactive nitrogen or carbon atom. Two possible reaction channels, water addition across the C=C bond or across the C horizontal lineN bond of ketenimine, are discussed. Our results indicate that the kinetically favorable mechanism involves an eight-membered ring transition state structure formed by a proton transfer chain of three water molecules. Meanwhile, two additional cooperative water molecules near the nonreactive region assist the hydration by engaging in hydrogen bonding to the substrate; such an interaction is found to be important in the hydration of ketenimine and other cumulenes. The lowest rate-determining activation barriers of C=C and C=N addition are 98.9 and 95.1 kJ/mol, respectively, suggesting that the two channels are competitive when more water molecules take part in the hydration. COSMO solution models do not modify the calculated energy barriers in a significant way.

Exploring the Reactivity Trends in the E2 and SN2 Reactions of X(-) + CH3CH2Cl (X = F, Cl, Br, HO, HS, HSe, NH2 PH2, AsH2, CH3, SiH3, and GeH3).

The reactivity order of 12 anions toward ethyl chloride has been investigated by using the G2(+) method, and the competitive E2 and SN2 reactions are discussed and compared. The reactions studied are X(-) + CH3CH2Cl → HX + CH2═CH2 + Cl(-) and X(-) + CH3CH2Cl → CH3CH2X + Cl(-), with X = F, Cl, Br, HO, HS, HSe, NH2 PH2, AsH2, CH3, SiH3, and GeH3. Our results indicate that there is no general and straightforward relationship between the overall barriers and the proton affinity (PA) of X(-); instead, discernible linear correlations only exist for the X's within the same group of the periodic table. Similar correlations are also found with the electronegativity of central atoms in X, deformation energy of the E2 transition state (TS), and the overall enthalpy of reaction. It is revealed that the electronegativity will significantly affect the barrier height, and a more electronegative X will stabilize the E2 and SN2 transition states. Multiple linear regression analysis shows that there is a reasonable linear correlation between E2 (or SN2) overall barriers and the linear combination of PA of X(-) and electronegativity of the central atom.