Core Unit Research Articles

Synthesis and Relaxivity study of amino acid-branched radical dendrimers as MRI contrast agents for potential brain tumor imaging.

This study introduces a series of water-soluble radical dendrimers (G0 to G5) as promising magnetic resonance imaging (MRI) contrast agents that could potentially address clinical safety concerns associated with current gadolinium-based contrast agents. By using a simplified synthetic approach based on a cyclotriphosphazene core and lysine-derived branching units, we successfully developed a G5 dendrimer containing up to 192 units of 2,2,6,6-Tetramethylpiperidinyloxy (TEMPO) radical. This synthesis offers advantages including ease of preparation, purification, and tunable water solubility through the incorporation of glutamic acid anion residues. Comprehensive characterization using 1H NMR, FT-IR, and SEC-HPLC confirmed the dendrimers' structures and purity. Electron paramagnetic resonance (EPR) spectroscopy revealed that TEMPO groups in higher generation dendrimers exhibited decreased mobility and stronger spin exchange in their local environments. In vitro MRI showed that relaxivity (r1) increased with higher dendrimer generations, with G5 exhibiting an exceptionally high r1 of over 24 mM-1s-1. Molecular dynamics simulations provided crucial insights into structure-property relationships, revealing the importance of water accessibility to TEMPO groups for enhancing relaxivity. Vero cell viability assay demonstrated G3 and G3.5 have good biocompatibility. In vivo MRI experiments in mice demonstrated that G3.5 was excreted through the kidneys and selectively accumulated in glioblastoma tumors. STATEMENT OF SIGNIFICANCE: This study explores a class of MRI contrast agents based on organic radical dendrimers as a potential alternative to gadolinium-based agents. We present a simplified synthesis method for water-soluble dendrimers containing up to 192 TEMPO radical units-the highest number achieved to date for this class of compounds-resulting in record-high relaxivity values. Our approach offers easier preparation, purification, and tunable water solubility, representing an improvement over existing methods. Through combined experimental and computational studies, we provide insights into the structure-property relationships governing relaxivity. In vivo experiments demonstrate the dendrimers' potential for glioblastoma imaging, with predominantly renal excretion. This work represents a step towards developing metal-free MRI contrast agents with promising relaxivity and biocompatibility, potentially opening new avenues for diagnostic imaging research.

Presaturated iron‐core fault current limiters for MVDC power system applications

AbstractThis paper presents design and dynamic performance investigation of a full‐scale, modular topology (arranged on the sides of a regular hexagon), medium voltage direct current (MVDC) permanent magnet (PM) biased presaturated fault current limiter (PMFCL). This PMFCL represents a cost‐effective design with enhanced longevity, reliability, scalability, and controllability. The scalability of this modular design can be extended by adding or removing CI (letters: CI) core units for different power system applications in a voltage range from to or more. The rated steady‐state (DC) and fault currents of and , respectively. The detection free and self‐triggering performance of this PMFCL is designed and simulated through a 3D coupled model of electric‐circuit magnetic‐field of COMSOL Multiphysics. Accurate representation of PM behaviour, especially in the second quadrant of its hysteresis loop of Jiles‐Atherton method gives realistic performance of the PMFCL. Comprehensive finite element simulations are carried out to study the effect of design parameters on the dynamic performance of PMFCL. Good agreement is found between COMSOL simulation results of DC‐biased PFCL and experimental results of a developed small‐scale prototype. Results reveal that the MVDC PMFCL shows significant improvement and satisfactory performance, in terms of fault current clipping ratio, fault current slope, and power losses, as compared to the conventional MVDC DC‐biased presaturated CI iron‐core fault current limiter (PFCL).

Photoinduced Electron Transfer System from Cesium Lead Bromide Quantum Dots to Naphthalenediimide Supramolecular Polymers.

Supramolecular polymers (SPs) formed via the stacking of π-conjugated molecules are attractive nanomaterials because of their potential optoelectronic properties derived from the non-covalent interaction between the π-skeletons. Especially, SPs possessing naphthalenediimide (NDI) core units can act as superior electron acceptors due to their deep lowest unoccupied molecular orbital (LUMO). Interaction of such SP with electron donors can realize a charge transfer system, but this has not been established. Herein, we report a photoinduced electron transfer system from cesium lead bromide quantum dot (QD) as an electron donor to SP composed of cholesterol-functionalized NDI derivatives. The supramolecular polymerization in a non-polar solvent was analyzed in detail via microscopic and spectroscopic analyses. Upon mixing the SP with QDs, the photoluminescence intensity and lifetime of QDs decreased significantly, indicating efficient photoinduced electron transfer from QD to SP.

Extension of the π-system of monoaryl-substituted norbornadienes with acetylene bridges: influence on the photochemical conversion and storage of light energy

Extension of the π-system of monoaryl-substituted norbornadienes with acetylene bridges: influence on the photochemical conversion and storage of light energy

Additive entanglement and intersectionality in UN human rights monitoring: examining the inclusion of disability

ABSTRACT This paper builds on intersectionality theory to provide a novel analytical approach for examining the inclusion of disability in the United Nations human rights monitoring processes. Notably, it develops the concept of additive entanglement to provide a lens for understanding the emergence of identity catalogues in human rights governance. To explain the effects of this type of entanglement, the article codes and analyses the references to disability in 2111 concluding observations of eight core United Nations Human Rights monitoring bodies from 2000 until 2018. By studying these types of discursive constructions, the article provides a conceptual approach to exploring the configuration of lists of identity categories in human rights governance. It offers an innovative technique for analysing how United Nations bodies form population clusters by privileging specific category combinations such as disability with age and gender when observing the human rights of persons with disabilities.

Non-fused Nonfullerene Acceptors with an Asymmetric Benzo[1,2-b:3,4-b', 6,5-b"]trithiophene (BTT) Donor Core and Different AcceptorTerminal Units for Organic Solar Cells.

Here in, we have designed two new unfused non-fullerene small molecules using asymmetric benzo[1,2-b:3.4-b', 6,5-b"]trithiophene (BTT) as the central donor core and different terminal units i. e., 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (NFA-4) and 1,3-diethyl-2-thioxodi hydropyrimidine-4,6 (1H,5H)-dione (NFA-5) and examined their optical and electrochemical properties. Using a wide band-gap copolymer D18, organic solar cells (OSCs) based on bulk heterojunction of D18:NFA-4 and D18:NFA-5 showed overall power conversion efficiency (PCE) of about 17.07 % and 11.27 %, respectively. The increased PCE for the NFA-4-based OSC, compared to NFA-5 counterpart, is due higher value of short circuit current (JSC), open circuit voltage (VOC), and fill factor (FF). Following the addition of small amount of NFA-5 to the binary bulk heterojunction D18:NFA-4, the ternary organic solar cells attained a PCE of 18.05 %, surpassing that of the binary counterparts due to the higher values of which is higher than that for the binary counterparts and attributed to the increased values of JSC, FF, and VOC. The higher value of JSC is linked to the efficient use to excitons transferred from NFA-5 to NFA-4 with a greated dipole moment than NFA-5 and subsequently dissociated into a free charge carrier efficiently.

Research and optimization of the gain characteristics of cascode amplifiers

Abstract. With the continuous development of IC technology, high-performance operational amplifiers are widely used in various circuit systems such as high-speed Analog-to-Digital Converters (ADCs), Digital-to-Analog Converters (DACs), switched capacitor filters, bandgap voltage reference sources, precision comparators. The amplifier has become the core unit circuit of analog IC and mixed-signal IC design, and its performance directly affects the overall performance of the circuit and system. The design of high-performance operational amplifiers has always been one of the hotspots in the research of analog IC design in order to meet the needs of various application fields. Cascode Amplifier is a classic structure widely used in high-frequency and high-gain electronic circuits. This project aims to study the gain characteristics of cascode amplifiers, explore the main factors affecting their gain, and propose methods to optimize the gain. Through theoretical analysis and simulation, the influence of different parameters on gain is verified. Then the optimization strategy is summarized to provide a reference for actual circuit design.

The paddlewheel complex of 1,8-naphthyridine and palladium(II)

This work presents the synthesis of the tetracationic paddlewheel complex of 1,8-naphthyridine and palladium(II), [Pd2(µ-napy)4]X4, (X = BF4− or PF6−). Single-crystal X-ray diffraction confirms a D4h symmetric paddlewheel structure encompassing the two Pd units in the metal core coordinated by four ditopic 1,8-naphthyridine ligands, featuring a relatively short Pd–Pd distance. Spectroscopic analyses combined with density-functional theory (DFT) provide insights into the nature of the Pd–Pd and Pd–Napy interactions as well as observed optical absorption frequencies.

13C NMR studies and orientational order of rod-like mesogens with strongly polar terminal cyano group

ABSTRACT 13C NMR studies of two rod-like mesogens with core units consisting of two and three phenyl rings with strongly polar terminal cyano groups are reported. The two-ring mesogen displayed an enantiotropic smectic A (SmA) mesophase while for the three-ring mesogen, enantiotropic nematic and SmA mesophases were observed. The solution 13C NMR studies of both the mesogens are carried out besides static 13C NMR measurements in the liquid crystalline phase. For the two-ring mesogen, the chemical shift anisotropy (CSA) tensors of the core unit are determined by the 2D-separation of undistorted powder patterns by effortless recoupling (SUPER) experiment. Furthermore, 2D-separated local field (SLF) measurements are realised for both the mesogens in the liquid crystalline phase to determine the 13C-1H dipolar couplings to find the orientational order parameters of the phenyl rings. The main order parameter (Szz) of the two-ring mesogen varies from 0.63 to 0.53 across the SmA phase and for the three-ring mesogen, the Szz values are found to be ~0.73 in the SmA phase and ~0.69 in the nematic phase. The CSA values determined from the SUPER experiment are expected to be a significant utility for molecules with polar terminal nitro/cyano groups as ferroelectric nematic phases are realised in them.

Barriers to the application of simulation technologies in the education of health care students

Abstract Simulation technologies (ST) in health and medical education are undergoing rapid development due to the undoubted advantages of the methods and forms of simulation used - high quality, significant efficiency, economy, reliability and safety for the patient. At the same time, the application of ST is still underrepresented in the education of health care students. The main aim of this study was to identify the barriers and perspectives for the application of ST in the education of health professional students in Bulgaria from the perspective of the respondents’ expertise. A qualitative study of the expert (n = 17) opinion of those directly involved in the introduction, application, and evaluation of the use of ST in the education of healthcare students was conducted in 2023 in Varna. The questionnaire regarding the barriers and perspectives in the use of ST in the education of undergraduate and postgraduate students in health specialties students was used. The main barriers to the widespread use of ST in the training of students were identified as follows: the lack of adapted curricula that combine traditional practical sessions with patients and those on simulators; the lack of a sufficient number of trained and motivated trainers; the reluctance of trainers to introduce or more widely use ST; lack of or insufficient space to locate a simulation centre or equipment in relevant core units; the high cost of purchasing and maintaining ST and limited financial resources, as well as the large number of students in the groups. According to one of the experts, ‘there are no barriers to the use of ST, but real patient contact and a personalized approach to the patient is impossible to replicate through technology,’ highlighting the importance in combining traditional training with real patients and modern with the use of technology. Ethical issues in training healthcare professionals with simulators appear to be a new aspect of medical education with the application of ST. Key messages • In the effort for widespread implementation of ST in the training of health professions students, it is important to achieve a balance with traditional training experienced with real patients. • Identifying and overcoming barriers is an important prerequisite for the rapid and widespread application of ST in the training of health care students.

13C CSA Tensors and Orientational Order of Model and Dimer Mesogens Comprising of Phenyl Benzoate.

A Model mesogen and its symmetrical Dimer made up of phenyl benzoate core unit are investigated by 13C NMR spectroscopy. The existence of layer order in smectic A and smectic C phases of Dimer mesogen is established by powder X-ray diffraction. The chemical shift anisotropy (CSA) tensors of Model mesogen are determined by 2D separation of undistorted powder patterns by effortless recoupling (SUPER) experiment and are utilized for calculating the order parameters employing the alignment-induced chemical shifts (AIS). Additionally, 2D separated local field (SLF) NMR is availed for extracting 13C-1H dipolar couplings for both mesogens and used for computing the order parameters. A good agreement in the order parameters calculated from 13C-1H dipolar couplings and AIS is observed. Accordingly, the main order parameter (Szz) for the phenyl rings of the Model mesogen is found to be in the range 0.54-0.82, and for the Dimer mesogen, the values span 0.64-0.82 across mesophases. Since the phenyl benzoate core unit is frequently employed structural moiety for constructing the main chain as well as side chain liquid crystalline polymers and liquid crystalline elastomers, the CSA tensors reported here will be of immense utility for the structural characterization of these materials.

Low-velocity impact on a CFRP sandwich plate with a reentrant auxetic core

Theoretical analysis is utilized to model the low-velocity impact (LVI) on a Carbon-Fiber Reinforced Polymer (CFRP) sandwich plate with reentrant auxetic core. The Zig-Zag theory is employed to formulate the displacement field of the sandwich plate. The mechanical characteristics of the reentrant auxetic core unit cell are determined through the application of Gibson’s equations. The influences of the unit cell thickness, the unit cell angle, the number of layers of the unit cell along the plate thickness, the impactor radius, and the impactor initial velocity on the LVI study of CFRP sandwich plate with reentrant auxetic core are investigated in detail.

Time-reversal symmetry breaking in the chemosensory array reveals a general mechanism for dissipation-enhanced cooperative sensing

The Escherichia coli chemoreceptors form an extensive array that achieves cooperative and adaptive sensing of extracellular signals. The receptors control the activity of histidine kinase CheA, which drives a nonequilibrium phosphorylation-dephosphorylation reaction cycle for response regulator CheY. Cooperativity and dissipation are both important aspects of chemotaxis signaling, yet their consequences have only been studied separately. Recent single-cell FRET measurements revealed that kinase activity of the array spontaneously switches between active and inactive states, with asymmetric switching times that signify time-reversal symmetry breaking in the underlying dynamics. Here, we present a nonequilibrium lattice model of the chemosensory array, which demonstrates that the observed asymmetric switching dynamics can only be explained by an interplay between the dissipative reactions within individual core units and the cooperative coupling between neighboring units. Microscopically, the switching time asymmetry originates from irreversible transition paths. The model shows that strong dissipation enables sensitive and rapid signaling response by relieving the speed-sensitivity trade-off, which can be tested by future single-cell experiments. Overall, our model provides a general framework for studying biological complexes composed of coupled subunits that are individually driven by dissipative cycles and the rich nonequilibrium physics within.

Investigation on the energy absorption characteristics of novel graded auxetic re-entrant honeycombs

In this work, innovative graded auxetic re-entrant honeycombs constructed by adjusting the geometric parameters of a core unit cell are proposed, and their deformation modes and energy absorption characteristics with different impact speeds are systematically investigated. The novel graded design utilizes structural hierarchy on the meso-scale and functional gradient on the macro-scale. The numerical simulation models are verified by comparing the experimental results. The results show that compared with the ungraded honeycomb (URH), one of the graded honeycombs (GRHs), named GRH1, can greatly improve the specific energy absorption by 36.4%, 10.8%, and 6.00% for the quasi-static, low, and high-speed impact at a strain of 0.6. At the same time, the initial peak stress of GRH1 is decreased by 43.2% and 27.1% compared with that of URH for low and high-speed impact, respectively. It could be indicated that the GRH1 was an ideal energy-absorbing structure. This work provides a new route for designing graded auxetic honeycombs with enough insight to understand the deformation mechanism of the structures, which could be used in lightweight buffer protective systems.

Organoboron Polymorphs with Different Molecular Packing Modes for Optical Waveguides.

Organoboron compounds offer a new strategy to design optoelectronic materials with high fluorescence efficiency. In this paper, the organoboron compound B-BNBP with double B←N bridged bipyridine bearing four fluorine atoms as core unit is facilely synthesized and exhibits a narrowband emission spectrum and a high photoluminescence quantum yield (PLQY) of 86.53 % in solution. Its polymorphic crystals were controllable prepared by different solution self-assembly methods. Two microcrystals possess different molecular packing modes, one-dimensional microstrips (1D-MSs) for H-aggregation and two-dimensional microdisks (2D-MDs) for J-aggregation, owing to abundant intermolecular interactions of four fluorine atoms sticking out conjugated plane. Their structure-property relationships were investigated by crystallographic analysis and theoretical calculation. Strong emission spectra with the full width at half maximum (FWHM) of less than 30 nm can also be observed in thin film and 2D-MDs. 1D-MSs possess thermally activated delayed fluorescence (TADF) property and exhibit superior optical waveguide performance with an optical loss of 0.061 dB/μm. This work enriches the diversity of polymorphic microcrystals and further reveals the structure-property relationship in organoboron micro/nano-crystals.

Study on the load capacity of prefabricated buckling-restrained braces with ductile steel castings based on singular function

Prefabricated buckling-restrained braces with ductile steel castings were used in the special concentrically braced frames to enable brace yield without buckling and prevent brittle failure of brace joints. This study presents a simplified three-segment calculation model subjected to axial force, based on the failure mode of the bracing system, utilizing singular function to derive formulas for the ultimate capacity of the braces. The accuracy of the computational formula was validated through numerical simulations and experimental findings. The outcomes indicate that the core unit of the brace undergoes third-order buckling deformation under axial force. The ultimate capacity of the braces is observed to increase with the cross-sectional area of the core unit but decrease with the length of the ductile steel castings. The theoretical values of the ultimate bearing capacity of the bracing system closely align with numerical simulations and experimental results, with error margins of 2.9 % to 9.3 % and 3.2 % to 4.6 %, respectively. These findings offer a theoretical foundation for the stability assessment of such brace configurations.

Exploiting macrocyclic polylactam for sensing V-series nerve agents: A computational study

The nerve agents are organophosphorus compounds (OPs) developed as chemical warfare agents (CWAs) that inhibit acetylcholinesterase (AChE) and lead to impeding neurological signals in mammals. Therefore, detecting such nerve agents is important, and efforts to study the fundamental interactions of host systems with CWAs are scarce in the literature. In this report, the cyclic 18-membered tetralactam [Ⅰ] as a host molecule has been chosen to sense V-series nerve agents. The DFT calculated results reveal that VM, VG, and VX, bind strongly with the core unit of the host molecule tetralactam [Ⅰ] with a preference for VM. The remarkably higher binding affinity of VM is governed by more hydrogen bonding interactions with the core of the cyclic 18-membered tetralactam [Ⅰ]. The nerve agent Russian VX has been found to bind weakly with the receptor molecule. The hydrogen bonding interactions of these nerve agents have further been analyzed with non-covalent interactions (NCI) and atoms in molecule (AIM) calculations. The tetralactam moiety exhibits the binding with V-series nerve agents and the absorption spectral results can be used as diagnostic signatures for sensing of such nerve agents in useful applications.

New Molecularly Flexible Self-Assembling Benzothiadiazole Derivatives: Mesomorphism And DFT Investigations

In the present study, we have synthesized symmetric/unsymmetrical BTD embedded self-assembling molecules and investigated for their mesomorphic properties. Two symmetrical series (BTDK-(2-18) and BTDC-(4-18)) comprises benzothiadiazole moiety as a central core unit which is connected to two different systematically varied end-groups, alkoxy ester and alkoxy coumaryl unit connected through ether and imine linkages. On the other hand, the asymmetric molecules have an alkoxy chalconyl unit at one end and a formyl group at the other. It was observed that, the mesomorphism is completely depends on the molecular flexibility. New molecules revealed mesomorphic behaviour with N (nematic), SmA (smectic-A) and SmC (smectic-C) mesophase with high thermal stability and greater range. Changes in mesogenic units (alkoxy ester & alkoxy coumaryl unit) and the impact of altering the alkoxy chain at both ends have been investigated. Interesting evaluation has been carried out on the molecular flexibility which resulted in different mesomorphic behaviour of molecules under study. Furthermore, the experimentally established values of the mesophase thermal stability (Tc) and mesophase temperature ranges (ΔTSmA, ΔTSmC, and ΔTN), as well as the type of the mesophase, were related to the calculated quantum chemical parameters (Frontier molecular orbitals (FMOs), Aspect Ratio, Polarizability, dipole moment, molecular and electrostatic potential (MEP)) that were obtained by using the DFT method of the investigated compounds.

Jaxspec : A fast and robust Python library for X-ray spectral fitting

Inferring spectral parameters from X-ray data is one of the cornerstones of high-energy astrophysics, and is achieved using software stacks that have been developed over the last 20 years and more. However, as models get more complex and spectra are obtained with higher resolutions, these established software solutions become more feature-heavy, difficult to maintain and less efficient. We present jaxspec a Python package for performing this task quickly and robustly in a fully Bayesian framework. Based on the JAX ecosystem jaxspec allows the generation of differentiable likelihood functions compilable on core or graphical process units (GPUs), enabling the use of robust algorithms for Bayesian inference. We demonstrate the effectiveness of jaxspec samplers, in particular the no U-turn sampler, using a composite model and comparing what we obtain with the existing frameworks. We also demonstrate its ability to process high-resolution spectroscopy data using original methods by reproducing the results of the Hitomi collaboration on the Perseus cluster, while solving the inference problem using variational inference on a GPU. We obtain identical results when compared to other software and approaches, meaning that jaxspec provides reliable results while being $ 10$ times faster than existing alternatives. In addition, we show that variational inference can produce convincing results even on high-resolution data in less than 10 minutes on a GPU. With this package, we aim to pursue the goal of opening up X-ray spectroscopy to the existing ecosystem of machine learning and Bayesian inference, enabling researchers to apply new methods to solve increasingly complex problems in the best possible way. Our long-term ambition is the scientific exploitation of the data from the newAthena X-ray Integral Field Unit (X-IFU).

Piezo tube stacked scanning tunneling microscope for use in extreme and confined environments

Scanning Tunneling Microscopy (STM) is widely used for observing atomic structures due to its ultra-high spatial resolution. As the core units of STM, the coarse stepper motor and imaging unit, have conflicting size requirements for piezo tubes. Longer piezo tubes yield greater output force and easier movement for the motor, while shorter tubes enhance imaging precision and stability for the scanner. Traditional STMs typically employ a large piezo tube for coarse stepping and a smaller one for independent imaging to address this issue. Here, we present the new design of a piezo tube stacked STM, in which two independent piezo tubes act together during tip-sample approach process and only one shorter tube works during scanning imaging. Both tubes are fixed to the framework, ensuring high rigidity and compactness. The new design enables us to achieve both coarse stepping and imaging functions with a total length of only 25 mm for the two tubes, effectively reducing the length of whole STM, facilitating its integration into narrow low-temperature spaces for imaging applications. Using this device, we obtained high-quality atomic images of graphite sample surfaces at room temperature. Continuous scanning imaging of the same area on Au film at 300 K demonstrates the STM’s high stability in both X-Y and Z directions. Atomic images, I-V spectra, and di/dv spectra obtained at 2 K on graphite surface illustrate the excellent application potential of this device in low-temperature environments. Finally, atomic images obtained of graphite in sweeping the magnetic fields from 0 T to 11 T in a huge vibrational dry magnet prove the new STM’s excellent performance in extreme conditions.