Chronic stroke survivors often suffer from gait impairment resistant to intervention. Recent rehabilitation strategies based on gait training with powered exoskeletons appear promising, but whether ...chronic survivors may benefit from them remains controversial. We evaluated the potential of exoskeletal gait training in restoring normal motor outputs in chronic survivors (N = 10) by recording electromyographic signals (EMGs, 28 muscles both legs) as they adapted to exoskeletal perturbations, and examined whether any EMG alterations after adaptation were underpinned by closer-to-normal muscle synergies. A unilateral ankle-foot orthosis that produced dorsiflexor torque on the paretic leg during swing was tested. Over a single session, subjects walked overground without exoskeleton (FREE), then with the unpowered exoskeleton (OFF), and finally with the powered exoskeleton (ON). Muscle synergies were identified from EMGs using non-negative matrix factorization. During adaptation to OFF, some paretic-side synergies became more dissimilar to their nonparetic-side counterparts. During adaptation to ON, in half of the subjects some paretic-side synergies became closer to their nonparetic references relative to their similarity at FREE as these paretic-side synergies became sparser in muscle components. Across subjects, level of inter-side similarity increase correlated negatively with the degree of gait temporal asymmetry at FREE. Our results demonstrate the possibility that for some survivors, exoskeletal training may promote closer-to-normal muscle synergies. But to fully achieve this, the active force must trigger adaptive processes that offset any undesired synergy changes arising from adaptation to the device's mechanical properties while also fostering the reemergence of the normal synergies.
Multiple bonds between boron and transition metals are known in many borylene (:BR) complexes via metal dπ→BR back‐donation, despite the electron deficiency of boron. An electron‐precise metal–boron ...triple bond was first observed in BiB2O− Bi≡B−B≡O− in which both boron atoms can be viewed as sp‐hybridized and the B−BO− fragment is isoelectronic to a carbyne (CR). To search for the first electron‐precise transition‐metal‐boron triple‐bond species, we have produced IrB2O− and ReB2O− and investigated them by photoelectron spectroscopy and quantum‐chemical calculations. The results allow to elucidate the structures and bonding in the two clusters. We find IrB2O− has a closed‐shell bent structure (Cs, 1A′) with BO− coordinated to an Ir≡B unit, (−OB)Ir≡B, whereas ReB2O− is linear (C∞v, 3Σ−) with an electron‐precise Re≡B triple bond, Re≡B−B≡O−. The results suggest the intriguing possibility of synthesizing compounds with electron‐precise M≡B triple bonds analogous to classical carbyne systems.
To bend or not to bend: Photoelectron spectroscopy and ab‐initio calculations show that IrB2O− has a bent (−OB)Ir≡B structure and ReB2O− has a linear structure, Re≡B−B≡O−. The latter is the first example of a transition‐metal borylyne complex.
Bismuth–Boron Multiple Bonding in BiB2O− and Bi2B Jian, Tian; Cheung, Ling Fung; Chen, Teng‐Teng ...
Angewandte Chemie International Edition,
August 1, 2017, Letnik:
56, Številka:
32
Journal Article
Recenzirano
Despite its electron deficiency, boron is versatile in forming multiple bonds. Transition‐metal–boron double bonding is known, but boron–metal triple bonds have been elusive. Two bismuth boron ...cluster anions, BiB2O− and Bi2B−, containing triple and double B−Bi bonds are presented. The BiB2O− and Bi2B− clusters are produced by laser vaporization of a mixed B/Bi target and characterized by photoelectron spectroscopy and ab initio calculations. Well‐resolved photoelectron spectra are obtained and interpreted with the help of ab initio calculations, which show that both species are linear. Chemical bonding analyses reveal that Bi forms triple and double bonds with boron in BiB2O− (Bi≡B−B≡O−) and Bi2B− (Bi=B=Bi−), respectively. The Bi−B double and triple bond strengths are calculated to be 3.21 and 4.70 eV, respectively. This is the first experimental observation of Bi−B double and triple bonds, opening the door to design main‐group metal–boron complexes with multiple bonding.
The more the merrier: Two bismuth–boron cluster anions, BiB2O− and Bi2B−, are shown to contain triple and double B−Bi bonds. The BiB2O− and Bi2B− clusters are produced by laser vaporization of a mixed B/Bi target. Well‐resolved photoelectron spectra were obtained and interpreted using ab initio calculations, showing that both species are linear.
BACKGROUND:Cervical collars are used after laminoplasty to protect the hinge opening, reduce risks of hinge fractures, and avoid spring-back phenomena. However, their use may lead to reduced range of ...motion and worse neck pain.
OBJECTIVE:To investigate the clinical, radiological, and functional outcomes of patients undergoing single-door laminoplasty with or without collar immobilization.
METHODS:This was a prospective, parallel, single-blinded randomized controlled trial. Patients underwent standardized single-door laminoplasty with mini-plates for cervical myelopathy and were randomly allocated into 2 groups based on the use of collar postoperatively. Clinical assessments included cervical range of motion, axial neck pain (VAS visual analogue scale), and objective scores (short-form 36-item, neck disability index, and modified Japanese Orthopaedic Association). All assessments were performed preoperatively and at postoperative 1, 2, 3, and 6 wk, and 3, 6, and 12 mo. Comparative analysis was performed via analysis of variance adjusted by baseline scores, sex, and age as covariates.
RESULTS:A total of 35 patients were recruited and randomized to collar use (n = 16) and without (n = 19). There were no dropouts or complications. There were no differences between groups at baseline. Subjects had comparable objective scores and range of motion at postoperative time-points. Patients without collar use had higher VAS at postoperative 1 wk (5.4 vs 3.5; P = .038) and 2 wk (3.5 vs 1.5; P = .028) but subsequently follow-up revealed no differences between the 2 groups.
CONCLUSION:The use of a rigid collar after laminoplasty leads to less axial neck pain in the first 2 wk after surgery. However, there is no additional benefit with regards to range of motion, quality of life, and complication risk.
Since the discovery of the B40 borospherene, research interests have been directed to the structural evolution of even larger boron clusters. An interesting question concerns if the borospherene ...cages persist in larger boron clusters like the fullerenes. Here we report a photoelectron spectroscopy (PES) and computational study on the structures and bonding of B41− and B42−, the largest boron clusters characterized experimentally thus far. The PE spectra of both clusters display broad and complicated features, suggesting the existence of multiple low-lying isomers. Global minimum searches for B41− reveal three low-lying isomers (I–III), which are all related to the planar B40− structure. Isomer II (Cs, 1A′) possessing a double hexagonal vacancy is found to agree well with the experiment, while isomers I (Cs, 3A′′) and III (Cs, 1A′) both with a single hexagonal vacancy are also present as minor isomers in the experiment. The potential landscape of B42− is found to be much more complicated with numerous low-lying isomers (VII–XII). The quasi-planar structure VIII (C1, 2A) containing a double hexagonal vacancy is found to make major contributions to the observed PE spectrum of B42−, while the other low-lying isomers may also be present to give rise to a complicated spectral pattern. Chemical bonding analyses show isomer II of B41− (Cs, 1A′) and isomer VIII of B42− (C1, 2A) are π aromatic, analogous to that in the polycyclic aromatic hydrocarbon C27H13+ (C2v, 1A1). Borospherene cage isomers are also found for both B41− and B42− in the global minimum searches, but they are much higher energy isomers.
In a high‐resolution photoelectron imaging and theoretical study of the IrB3− cluster, two isomers were observed experimentally with electron affinities (EAs) of 1.3147(8) and 1.937(4) eV. Quantum ...calculations revealed two nearly degenerate isomers competing for the global minimum, both with a B3 ring coordinated with the Ir atom. The isomer with the higher EA consists of a B3 ring with a bridge‐bonded Ir atom (Cs , 2A′), and the second isomer features a tetrahedral structure (C3v , 2A1). The neutral tetrahedral structure was predicted to be considerably more stable than all other isomers. Chemical bonding analysis showed that the neutral C3v isomer involves significant covalent Ir−B bonding and weak ionic bonding with charge transfer from B3 to Ir, and can be viewed as an Ir–(η3‐B3+) complex. This study provides the first example of a boron‐to‐metal charge‐transfer complex and evidence of a π‐aromatic B3+ ring coordinated to a transition metal.
Two at a minimum: High‐resolution photoelectron imaging and ab initio calculations (see picture) identified two isomers of IrB3− that compete for the global minimum in the anion. Bonding analysis revealed that an η2‐B3 isomer is stabilized by covalent interactions, whereas an η3‐B3 isomer is more ionic with the negative charge transferred to Ir to form a (B3)+Ir− complex.
We report the observation of a dipole-bound state (DBS) 659 cm–1 below the electron detachment threshold of cryogenically cooled deprotonated 4,4′-biphenol anion (bPh–) and 19 of its lowest ...vibrational levels. Resonant two-photon photoelectron imaging (R2P-PEI) via the vibrational levels of the DBS displays a sharp peak with a constant binding energy. This observation indicates vertical detachment from the vibrational levels of the DBS to the corresponding neutral levels with the conservation of the vibrational energy, suggesting that the highly diffuse electron in the DBS has little effect on the neutral core. The R2P-PEI spectra also exhibit two features at lower binding energies, which come from intersystem crossings from the DBS to two lower-lying valence-bound triplet excited states of bPh–. The current study discloses the first R2P-PEI spectra from vibrational excited states of a DBS and direct spectroscopic evidence of transitions from a DBS to valence-bound states of anions.
A dipolar molecule can weakly bind an electron in a diffuse orbital. However, the spin-orbit coupling between this weakly bound electron and the electrons in the molecular core is not known. Here we ...probe this coupling using the linear C
P
anion with the
Σ
ground state, which possesses dipole-bound excited states because neutral C
P (
Π) has a sufficiently large dipole moment. Photodetachment spectroscopy and resonant photoelectron spectroscopy are used to probe the nature of the dipole-bound states. Two dipole-bound excited states are observed with a binding energy of 37 cm
, corresponding to the two spin-orbit states of neutral C
P (
Π
and
Π
). The current study demonstrates that the weakly bound electron in the dipole-bound excited states of C
P
is not spin-coupled to the electrons in the C
P core and can be considered as a quasi-free electron.
Vibrational state-selective resonant two-photon photoelectron spectra have been obtained via a triplet intermediate state (3Σ–) of AuS– near its detachment threshold using high-resolution ...photoelectron imaging of cryogenically cooled AuS– anions. Four vibrational levels of the 3Σ– excited state are observed to be below the detachment threshold. Resonant two-photon absorptions through these levels yield vibrational state-selective photoelectron spectra to the 2Σ final state of neutral AuS with broad and drastically different Franck–Condon distributions, reflecting the symmetries of the vibrational wave functions of the 3Σ– intermediate state. The 3Σ– excited state is spin-forbidden from the 1Σ+ ground state of AuS– and is accessed due to strong relativistic effects. The nature of the 3Σ– excited state is confirmed by angular distributions of the photoelectron images and quantum calculations.
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