Axial Centers Research Articles

Medial-pivot total knee arthroplasty enhances tibiofemoral axial rotation stability in weight-bearing mid-range flexion compared to posterior-stabilised system.

Total knee arthroplasty (TKA) stands as a primary intervention for severe knee ailments, yet concerns remain regarding postoperative patient satisfaction and flexion instability. This study aims to evaluate the in-vivo kinematics of medial-pivot (MP) and posterior-stabilised (PS) designs during step-up activity, in comparison to the kinematics of the nonoperated contralateral knee. Sixteen patients with PS-TKA and 14 with MP-TKA were retrospectively examined. Clinical outcomes were assessed using patient-completed questionnaires. Motion during step-up was captured using a dual fluoroscopic system. Statistical analysis was applied to evaluate the in-vivo tibiofemoral six-degree-of-freedom kinematics and articular contact positions between the two groups. Despite being older, patients in the MP group reported higher postoperative subjective scores for weight-bearing functional activities. The axial rotation centres of MP-TKA located on the medial tibial plateau exhibited less variance compared to PS-TKA and contralateral knees. Compared to the contralateral knee (contralateral to medial-pivot [C-MP] or contralateral to posterior-stabilised [C-PS]), the MP group exhibited limited range of motion in terms of anteroposterior translation (MP: 3.6 ± 1.3 mm vs. C-MP: 7.4 ± 2.5 mm, p < 0.01) and axial rotation (MP: 6.6 ± 1.9° vs. C-MP: 10.3 ± 4.9°, p = 0.02), as well as in the PS group for anteroposterior translation (PS: 3.9 ± 1.7 mm vs. C-PS: 7.2 ± 3.7 mm, p < 0.01). The MP group with better postoperative ratings demonstrated a more stable MP axial rotation pattern during step-up activity compared to the PS group, underscoring the pivotal role of prosthetic design in optimising postoperative rehabilitation and functional recovery. Level III.

14N Hyperfine and nuclear interactions of axial and basal NV centers in 4H-SiC: A high frequency (94 GHz) ENDOR study

The nitrogen-vacancy (NV) centers (NCVSi)− in 4H silicon carbide (SiC) constitute an ensemble of spin S = 1 solid state qubits interacting with the surrounding 14N and 29Si nuclei. As quantum applications based on a polarization transfer from the electron spin to the nuclei require the knowledge of the electron–nuclear interaction parameters, we have used high-frequency (94 GHz) electron–nuclear double resonance spectroscopy combined with first-principles density functional theory to investigate the hyperfine and nuclear quadrupole interactions of the basal and axial NV centers. We observed that the four inequivalent NV configurations (hk, kh, hh, and kk) exhibit different electron–nuclear interaction parameters, suggesting that each NV center may act as a separate optically addressable qubit. Finally, we rationalized the observed differences in terms of distinctions in the local atomic structures of the NV configurations. Thus, our results provide the basic knowledge for an extension of quantum protocols involving the 14N nuclear spin.

Influence of (N,H)-terminated surfaces on stability, hyperfine structure, and zero-field splitting of NV centers in diamond

We present a density functional theory analysis of the negatively charged nitrogen-vacancy (${\mathrm{NV}}^{\ensuremath{-}}$) defect complex in diamond located in the vicinity of (111)- or (100)-oriented surfaces with mixed (N,H)-terminations. We assess the stability and electronic properties of the ${\mathrm{NV}}^{\ensuremath{-}}$ center, and we study their dependence on the H:N ratio of the surface termination. The formation energy, the electronic density of states, the hyperfine structure, and the zero-field-splitting parameters of an ${\mathrm{NV}}^{\ensuremath{-}}$ center are analyzed as a function of its distance and orientation to the surface. We find stable ${\mathrm{NV}}^{\ensuremath{-}}$ centers with bulklike properties at distances of at least $\ensuremath{\sim}8$ \AA{} from the surface provided that the surface termination consists of at least 25% substitutional nitrogen atoms. The studied surface terminations have a minor effect on the ground-state properties, whereas the NV orientation has major effects. Our results indicate that axial NV centers near a flat 100% N-terminated (111) surface are the optimal choice for NV-based quantum sensing applications as they are the least influenced by the proximity of the surface.

Multi-stage melting of enriched mantle components along the eastern Gakkel Ridge

The global endmember ultra-slow spreading Arctic Gakkel ridge is an ideal place to study mantle melting and the contributions of different mantle components to ridge volcanism. We carried out a high-resolution geochemical study of basalts from a seemingly normal section of the ultraslow-spreading Arctic Gakkel Ridge between 40°E and 60°E, which we refer to as EVZ2. While the majority of volcanics sampled from EVZ2 could be characterized as normal Mid-Ocean Ridge Basalts (NMORB), we identified a group of Isotopically Enriched, Incompatible Element Depleted MORB (IEDMORB) with low MREE/HREE ratios (i.e., “ghost garnet” signature). EVZ2 IEDMORB are mostly found near the rift valley walls away from axial volcanic centers. We propose that IEDMORB are the products of two stages of melting. They are shallow secondary melts of incompatible trace element enriched low-solidus mantle components that had lost some initial melt in the presence of residual garnet at depth. While the deep initial melts are more likely to be focused toward axial volcanic centers and subsequently diluted by normal peridotite melts, some of the shallow secondary melts could erupt as IEDMORB via pre-existing crustal weaknesses, such as deep-rooted high-angle normal faults that are ubiquitous along ultra-slow spreading ridges, thereby preserving their enriched isotopic compositions. While most dredges that sampled IEDMORB also recovered other types of MORB, all the samples from Dredge 55 are IEDMORB with distinctive arc-type trace element signatures, including relative depletion in Nb (and Ta), as well as enrichment in Th and fluid mobile elements (e.g., high Th/Nb, La/Nb, Pb/Ce, and H2O/Ce). These signatures suggest that they sampled recycled metasomatized arc-mantle wedge material. Other EVZ2 IEDMORB also show relative enrichment in fluid mobile elements and depletion in Nb (e.g., high La/Nb), but lack enrichment in Th. As Th has extremely low mobility in aqueous fluids, Th enrichment requires metasomatism involving silicate melts. Thus, we propose that the high Th/Nb, high La/Nb IEDMORB contain silicate-melt metasomatized arc mantle wedge material while the low-Th/Nb, high La/Nb IEDMORB only contain aqueous-fluid metasomatized arc mantle wedge material. Globally, IEDMORB with ghost garnet signatures are mostly found along ridges near mantle plumes where low-solidus, incompatible element and isotopically enriched mantle components that suffered initial melt loss at depth could be entrained in the upwelling subridge mantle and undergo further melting. However, most near-plume IEDMORB do not show arc-type geochemical signatures. Therefore, the discovery of IEDMORB from 20% of dredges along EVZ2, where most ridge volcanics are NMORB with depleted isotopic compositions, reflects the sporadic distribution of recycled arc mantle wedge material in the Arctic mantle and the prevalence of pre-existing crustal conduits, such as high-angle normal faults, along ultra-slow spreading ridges that facilitate melt migration with limited melt pooling and mixing.

Atomic spin and phonon coupling mechanism of nitrogen-vacancy center

The nitrogen-vacancy center structure of diamond has attracted widespread attention due to its high sensitivity in quantum precision measurement. In this paper, a coupled phonon field is used to resonantly regulate the atomic spins of the nitrogen-vacancy center for improving the spin transition efficiency. Firstly, the interaction between phonons and lattice energy is analyzed based on the relationship between the wave function and the lattice displacement vector. The spin transition mechanism is investigated based on phonon resonance regulation, and the strain-induced energy transferable phonon-spin interaction coupling excitation model is established. Secondly, the coefficient matrix satisfying Bloch’s theorem is adopted to develop the phonon spectrum model of the first Brillouin zone characteristic region for different axial nitrogen-vacancy centers. Considering the thermal expansion, the thermal balance properties of phonon resonance system are analyzed and its specific heat model is studied based on the Debye model. Finally, the structure optimization model of different axial nitrogen-vacancy centers under the phonon model is built up based on the molecular dynamics simulation software CASTEP and density functional theory for first-principles research. The structural characteristics, phonon characteristics, and thermodynamic properties of nitrogen-vacancy centers are analyzed. The research results show that the evolution of phonon mode depends on the occupation of the nitrogen-vacancy center. A decrease in thermodynamic entropy accompanies the strengthening of the phonon mode. The covalent bond of diamond with nitrogen-vacancy center is weaker than that of a defect-free diamond. The thermodynamic properties of a defect-free diamond are more unstable. The primary phonon resonance frequency of diamond with nitrogen-vacancy centers are on the order of THz, and the secondary phonon resonance frequency is about in a range of 800 and 1200 MHz. A surface acoustic wave resonance mechanism with an interdigital width of 1.5 μm is designed according to the secondary resonance frequency, and its center frequency is about 930 MHz. The phonon resonance control method can effectively increase the spin transition probability of nitrogen-vacancy center under suitable phonon resonance control parameters, and thus realizing the increase of atomic spin manipulation efficiency.

Парамагнитные центры Mn-=SUP=-2+-=/SUP=-, Gd-=SUP=-3+-=/SUP=- и Cu-=SUP=-2+-=/SUP=- в легированном хромом монокристалле Li-=SUB=-2-=/SUB=-CaSiO-=SUB=-4-=/SUB=-

In the Li2CaSiO4 crystal, in addition to intense axial centers of Cr4+, the EPR spectra of impurity ions Mn2+ (S = 5/2), Gd3+ (S = 7/2), and Cu2+ (S = 1/2) have been discovered and studied. Manganese and gadolinium ions exhibit spectra of tetragonal symmetry, copper ions are represented by spectra of both axial and triclinic symmetry. The parameters of the spin Hamiltonians of tetragonal centers are determined. It was shown that Mn2+ and Gd3+ ions substitute for calcium ions with an eightfold oxygen environment, copper ions are localized in lithium positions with a tetrahedral environment. The reasons for the appearance of Cu2+ triclinic centers are discussed.

Reconstruction of vector static magnetic field by different axial NV centers using continuous wave optically detected magnetic resonance in diamond**Project supported by the National Natural Science Foundation of China (Grant Nos. 11305074, 11135002, 11804112, and 11275083), the Key Program of the Education Department Outstanding Youth Foundation of Anhui Province, China (Grant No. gxyqZD2017080), the Natural Science Foundation of Anhui Province,

We carried out a proof-of-principle demonstration of the reconstruction of a static vector magnetic field involving adjacent three nitrogen-vacancy (NV) sensors with corresponding different NV symmetry axes in a bulk diamond. By means of optical detection of the magnetic resonance (ODMR) techniques, our experiment employs the continuous wave (CW) to monitor resonance frequencies and it extracts the information of the detected field strength and polar angles with respect to each NV frame of reference. Finally, the detected magnetic field relative to a fixed laboratory reference frame was reconstructed from the information acquired by the multi-NV sensor.

Electron paramagnetic resonance tagged high-resolution excitation spectroscopy of NV-centers in 4H -SiC

We show that electron paramagnetic resonance (EPR) tagged high resolution photoexcitation spectroscopy is a powerful method for the correlation of zero phonon photoluminescence spectra with atomic point defects. Applied to the case of NV centers in $4H$-SiC it allows to associate the photoluminescence zero phonon lines (ZPL) at 1243, 1223, 1180, and 1176 nm with the (hk, kk, hh, kh) configurations of the ${\mathrm{NV}}^{\ensuremath{-}}$centers in this material. These results lead to a revision of a previous tentative assignment. Contrary to theoretical predictions, we find that the NV centers in $4H$-SiC show a negligible Franck-Condon shift as their ZPL absorption lines are resonant with the ZPL emission lines. The high subnanometer energy resolution of this technique allows us further to resolve additional fine-structure of the ZPL lines of the axial NV centers which show a doublet structure with a splitting of 0.8 nm. Our results confirm that NV centers in $4H$-SiC provide strong competitors for sensing and qubit application due to the shift of their optical transitions into the technology compatible near-infrared region and the superior material properties of SiC. Given that single center spin readout will be realized, they are suitable for scalable nanophotonic devices compatible with optical communication network.

Luminescence at the axial centers of CdP2-D48 crystals

Emission lines of free excitons and excitons bound to axial centers have been observed in the luminescence spectra of CdP2-D48 crystals doped with Mn, Sn, and Sb at 10 K. Bands models of excitons bound to axial centers (Mn, Sn, Sb) are proposed. The luminescence of crystals doped with Fe does not correspond to the axial centers band scheme. It is shown that direct transitions in excitonic band are polarized and in the case of indirect transitions they ate unpolarized. The direct band gap is due to allowed transitions Г1 → Г1 and Г2 → Г1 in E||c and E⊥c polarizations, respectively. The coefficient of the energy shift in the temperature range of 2–10 K in E‖c and Е⊥c polarizations differs (ΔE/ΔT = 3.5 meV/K, E‖c and 1 meV/K, Е⊥c).

C-Arm Image-Based Surgical Path Planning Method for Distal Locking of Intramedullary Nails.

Due to the curvature of the bone marrow cavity, the intramedullary nail used in long bone fracture fixation can be deformed, causing displacement of the locking holes. In this study, an algorithm using only one C-arm image to determine the center positions and axial directions of locking holes was developed for drilling guidance. Based on conventional method that the axial direction of locking hole would be identified when locking hole contour is presented as a circle, the proposed method can locate the circle contour centroid by using one C-arm image including two elliptical contours. Then the two distal locking holes' axial direction and centers would be determined. Three experiments were conducted to verify the performance of the proposed algorithm, which are (1) computer simulation, (2) use of real intramedullary nails, and (3) actual drilling test with the bone model. The experimental results showed that the average error of the axial direction and center position were 0.62 ± 0.6°, 0.73 ± 0.53 mm (simulation) and 3.16 ± 1.36°, 1.10 ± 0.50 mm (actual nail), respectively. The last ten drilling test sets were completed successfully (with an average duration of 48 seconds). Based on the experimental results, the proposed algorithm was feasible for clinic applications.

ChemInform Abstract: A Facile Synthesis of Novel Allenylphosphinates Containing Multi Potential Asymmetric Centers.

The novel allenylphosphinates containing up to three axial and phosphorus asymmetric centers were prepared in excellent yields via the reactions of 6-chloro-6H-dibenzo[c,e][1,2]oxaphosphinine to propargyl alcohols. During the process, the configuration of phosphorus determined the biphenyl axial chirality, stereospecifically forming (l)-stereomers but did not influence the chirality of allenyl axis.

NV centers in3C,4H, and6Hsilicon carbide: A variable platform for solid-state qubits and nanosensors

The outstanding magneto-optical properties of the nitrogen-vacancy (NV) center in diamond have stimulated the search for similar systems. We show here that NV triplet centers can also be generated in all the main SiC polytypes. We have identified by electron paramagnetic resonance spectroscopy and first-principles calculations the axial ${\mathrm{NV}}^{\ensuremath{-}}$ pairs in $3C,4H$, and $6H$ SiC, showing polytype and lattice site-specific magnetic and optical properties. We demonstrate very efficient room-temperature spin polarization of the ground state upon near infrared optical excitation for the NV center in $3C$ SiC and axial NV centers in the hexagonal $(4H,6H)$ polytypes; the signals of basal pairs are much lower in intensity. Axial NV centers in hexagonal SiC polytypes and thus constitute unidirectional ensembles which may be useful in nanosensing applications.

Desymmetrization of an Octahedral Coordination Complex Inside a Self-Assembled Exoskeleton.

The synthesis of a centrally functionalized, ribbon-shaped [6]polynorbornane ligand L that self-assembles with Pd(II) cations into a {Pd2 L4 } coordination cage is reported. The shape-persistent {Pd2 L4 } cage contains two axial cationic centers and an array of four equatorial H-bond donors pointing directly towards the center of the cavity. This precisely defined supramolecular environment is complementary to the geometry of classic octahedral complexes [M(XY)6 ] with six diatomic ligands. Very strong binding of [Pt(CN)6 ](2-) to the cage was observed, with the structure of the host-guest complex {[Pt(CN)6 ]@Pd2 L4 } supported by NMR spectroscopy, MS, and X-ray data. The self-assembled shell imprints its geometry on the encapsulated guest, and desymmetrization of the octahedral platinum species by the influence of the D4h -symmetric second coordination sphere was evidenced by IR spectroscopy. [Fe(CN)6 ](3-) and square-planar [Pt(CN)4 ](2-) were strongly bound. Smaller octahedral anions such as [SiF6 ](2-) , neutral carbonyl complexes ([M(CO)6 ]; M=Cr, Mo, W) and the linear [Ag(CN)2 ](-) anion were only weakly bound, showing that both size and charge match are key factors for high-affinity binding.

A Facile Synthesis of Novel Allenylphosphinates Containing Multi Potential Asymmetric Centers

The novel allenylphosphinates containing up to three axial and phosphorus asymmetric centers were prepared in excellent yields via the reactions of 6‐chloro‐6H‐dibenzo[c,e][1,2]oxaphosphinine to propargyl alcohols. During the process, the configuration of phosphorus determined the biphenyl axial chirality, stereospecifically forming (l)‐stereomers but did not influence the chirality of allenyl axis.

Manifestation of spin-dependent recombination in afterglow of zinc oxide crystals

Long-lasting afterglow of ZnO single crystals grown by hydrothermal method has been studied using high-frequency (94 GHz) optically detected magnetic resonance (ODMR) at helium temperatures. Giant (up to 30%) afterglow intensity-detected electron paramagnetic resonance signals of shallow donors and deep acceptors, which are lithium atoms substituting for zinc in the ZnO lattice, unambiguously indicate a spin-dependent character of the donor-acceptor recombination. The observed variations in the shape of the afterglow-detected ODMR spectra of lithium acceptors with time passed after irradiation are associated with the difference in the recombination rates of shallow donors with axial and non-axial LiZn centers and with a change in the recombination character with time.

Comparative EPR study CO2− radicals in modern and fossil tooth enamel

Comparative EPR investigation of CO2− radicals in modern (γ-irradiated) and fossil samples of tooth enamel was performed. The samples studied were the enamel powders and plates, the latter demonstrating an orientation dependence of EPR spectra in an external magnetic field. It was found that the ratio between the axial and orthorhombic CO2− centers amounts appears to be different for modern and fossil enamels. This ratio can be estimated by modeling of EPR spectra lineshape of powders or, in the case of plates, from the orientation dependence of EPR spectra in an external magnetic field. It was assumed that the difference between modern and fossil enamels is caused by the transformation, in the course of time, of orthorhombic CO2− centers into axial ones. The equations that describe this process were deduced. Their solutions show that the ratio between the amounts of the axial and orthorhombic centers does not depend on the dose rate. This finding can be used for the development of the method to determine the fossil enamel age avoiding the determination of the annual dose.

Effects of Wavenumber and Chirality on the Axial Compressive Behavior of Wavy Carbon Nanotubes: A Molecular Mechanics Study

The effects of wavenumber and chirality on the axial compressive behavior and properties of wavy carbon nanotubes (CNTs) with multiple Stone‐Wales defects are investigated using molecular mechanics simulations with the adaptive intermolecular reactive empirical bond‐order potential. The wavy CNTs are assumed to be point‐symmetric with respect to their axial centers. It is found that the wavy CNT models, respectively, exhibit a buckling point and long wavelength buckling mode regardless of the wavenumbers and chiralities examined. It is also found that the wavy CNTs have nearly the same buckling stresses as their pristine straight counterparts.

Optical properties and band structure of ZnP2-D48

The emission lines of bound and free excitons and their phonon replicas were observed in the luminescence spectra of ZnP2-D48 crystals doped with Mn, Sn, Cd and Sb measured at 10K. The emission lines are described by the model of axial center levels. Models of the bands of the bound excitons with different axial centers (Mn, Sn, Cd and Sb) are presented. It was observed that the indirect transitions in the excitonic bands were nonpolarized and that the direct transitions were polarized. The minimal direct energy gaps in the polarization E∥c are due to the allowed Г1→Г1 transitions, and the gaps in the polarization E⊥c are due to the Г2→Г1 transitions. The temperature shift coefficient of the bands gaps differs for different polarizations in the temperature interval from 2 to 10K (ΔE/ΔT=3.5meV/K and 1meV/K for E∥c and E⊥c, respectively). The optical constants n, k, ε1, ε2,d2ε1/dE2 and d2ε2/dE2 were calculated for the energy interval 1.5–10eV using the Kramers-Kronig analysis of measured reflection spectra. The features observed in these spectra were interpreted using two types theoretical calculations of band structure as optical transitions.

Effect on Position of Electromagnetic Stirring on Inclusion Behaviors in Billet

A considerable number of research works have been carried out to study the effects of electric current and frequency of Electromagnetic Stirring (EMS) on the quality of cast steels, but there are only a few studies available addressing the effects of EMS location on inclusion removal and steel cleanliness An ideal position of EMS will improve inclusion floatation and separation from liquid steel. However, inappropriate installation will lead to the entrapment of the slag into liquid steel, and impact the quality of cast billet. The current applied for these plant trials was 300A at a frequency of 3Hz,positions form axial centers of EMS to the top of the mold were 450mm, 510mm and 690mm respectively . 130 billets of medium carbon steel were produced and samples were taken for spectral analysis to study the effects of installation location of EMS on steel cleanliness. The experimental results show that the optimum position of EMS should be placed 510mm from the top end of the copper mold when the electrical current is 300A at frequency of 3 Hz. The three parameters of placement of EMS in paper were obtained from the simulation results, and this paper focused mainly on the effect EMS position on inclusion behaviors in billet.

A [2 × 2] Cu4 molecular grid and a Mn5 cluster derived from a 1-(2-pyridyl)pyrazole based polytopic ligand – Synthesis, structure, magnetic properties and catalytic activity in the allylic oxidation of cyclohexene

The homoleptic [2×2] tetranuclear compound [Cu4(PyPzCAP)4](NO3)4·8H2O (1) and the pentanuclear Mn(II) cluster [Mn5(PyPzCAP)6](ClO4)4·4C6H6 (2) are self-assembled from the ditopic pro-ligand HPyPzCAP [(5-methyl-1-(pyridin-2-yl)-N′-[1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3-carbohydrazide)]. Complex 1 is almost a square grid, and all the Cu(II) centers show a distorted octahedral environment with an N4O2 chromophore. Complex 2 has a pentanuclear core with a trigonal bipyramidal arrangement of the Mn(II) atoms. The axial Mn centers bear an N3O3 chromophore and the equatorial centers have an N4O2 distorted octahedral arrangement. Complex 1 shows a ferromagnetic exchange interaction (J=+4.62cm−1 and g=2.05), whereas 2 shows weak an antiferromagnetic interaction (J=−2.73cm−1 and g=2.02). Both complexes 1 and 2 catalyze the allylic oxidation of cyclohexene to cyclohex-2-ene-1-one with good selectivity and an excellent overall turnover number.