15 research outputs found
Trade-offs among cost, integration, and segregation in the human connectome
AbstractThe human brain structural network is thought to be shaped by the optimal trade-off between cost and efficiency. However, most studies on this problem have focused on only the trade-off between cost and global efficiency (i.e., integration) and have overlooked the efficiency of segregated processing (i.e., segregation), which is essential for specialized information processing. Direct evidence on how trade-offs among cost, integration, and segregation shape the human brain network remains lacking. Here, adopting local efficiency and modularity as segregation factors, we used a multiobjective evolutionary algorithm to investigate this problem. We defined three trade-off models, which represented trade-offs between cost and integration (Dual-factor model), and trade-offs among cost, integration, and segregation (local efficiency or modularity; Tri-factor model), respectively. Among these, synthetic networks with optimal trade-off among cost, integration, and modularity (Tri-factor model [Q]) showed the best performance. They had a high recovery rate of structural connections and optimal performance in most network features, especially in segregated processing capacity and network robustness. Morphospace of this trade-off model could further capture the variation of individual behavioral/demographic characteristics in a domain-specific manner. Overall, our results highlight the importance of modularity in the formation of the human brain structural network and provide new insights into the original cost-efficiency trade-off hypothesis
Disrupted Functional Brain Connectome in Individuals at Risk for Alzheimer's Disease
Background: Alzheimer's disease disrupts the topological architecture of whole-brain connectivity (i.e., the connectome); however, whether this disruption is present in amnestic mild cognitive impairment (aMCI), the prodromal stage of Alzheimer's disease, remains largely unknown. Methods: We employed resting-state functional magnetic resonance imaging and graph theory approaches to systematically investigate the topological organization of the functional connectome of 37 patients with aMCI and 47 healthy control subjects. Frequency-dependent brain networks were derived from wavelet-based correlations of both high-and low-resolution parcellation units. Results: In the frequency interval .031-.063 Hz, the aMCI patients showed an overall decreased functional connectivity of their brain connectome compared with control subjects. Further graph theory analyses of this frequency band revealed an increased path length of the connectome in the aMCI group. Moreover, the disease targeted several key nodes predominantly in the default-mode regions and key links primarily in the intramodule connections within the default-mode network and the intermodule connections among different functional systems. Intriguingly, the topological aberrations correlated with the patients' memory performance and differentiated individuals with aMCI from healthy elderly individuals with a sensitivity of 86.5% and a specificity of 85.1%. Finally, we demonstrated a high reproducibility of our findings across different large-scale parcellation schemes and validated the test-retest reliability of our network-based approaches. Conclusions: This study demonstrates a disruption of whole-brain topological organization of the functional connectome in aMCI. Our finding provides novel insights into the pathophysiological mechanism of aMCI and highlights the potential for using connectome-based metrics as a disease biomarker
Whole brain functional connectivity in clinically isolated syndrome without conventional brain MRI lesions
Objective To investigate brain functional connectivity (FC) alterations in patients with clinically isolated syndromes (CIS) presenting without conventional brain MRI lesions, and to identify the FC differences between the CIS patients who converted to multiple sclerosis (MS) and those not converted during a 5-year follow-up. Methods We recruited 20 CIS patients without conventional brain lesions, 28 patients with MS and 28 healthy controls (HC). Normalized voxel-based functional connectivity strength (nFCS) was determined using resting-state fMRI (R-fMRI) and compared among groups. Furthermore, 5-years clinical follow-up of the CIS patients was performed to examine the differences in nFCS between converters and non-converters. Results Compared to HC, CIS patients showed significantly decreased nFCS in the visual areas and increased nFCS in several brain regions predominately in the temporal lobes. MS patients revealed more widespread higher nFCS especially in deep grey matter (DGM), compared to CIS and HC. In the four CIS patients converting to MS, significantly higher nFCS was found in right anterior cingulate gyrus (ACC) and fusiform gyrus (FG), compared to non-converted patients. Conclusion We demonstrated both functional impairment and compensation in CIS by R-fMRI. nFCS alteration in ACC and FG seems to occur in CIS patients at risk of developing MS
Mechanism of the Mn Promoter via CoMn Spinel for Morphology Control: Formation of Co<sub>2</sub>C Nanoprisms for FischerāTropsch to Olefins Reaction
The
FischerāTropsch to olefins (FTO) reaction over Co<sub>2</sub>C catalysts is structure-sensitive, as the catalytic performance
is strongly influenced by the surface structure of the active phase.
The exposed facets determine the surface structure, and it remains
a great challenge to precisely control the particle morphology of
the FTO active phase. In this study, the controlling effect of the
Mn promoter on the final morphology of the Co<sub>2</sub>C nanoparticles
for the FTO reaction was investigated. The unpromoted catalyst and
several promoted catalysts with Ce, La, and Al were also studied for
comparison. For the Mn-promoted catalysts, the combination method
of the Co and Mn components plays a crucial role in the final morphology
of Co<sub>2</sub>C and thus the catalytic performance. For the CoMn
catalyst prepared by coprecipitation, Co<sub>2</sub>C nanoprisms with
specifically exposed facets of (101) and (020) can be obtained, which
exhibit a promising FTO catalytic performance with high C<sub>2ā4</sub><sup>=</sup> selectivity, low methane selectivity, and high activity
under mild reaction conditions. However, for the Mn/Co catalyst prepared
via impregnation, Co<sub>2</sub>C nanospheres are formed, which exhibit
high methane selectivity, low C<sub>2ā4</sub><sup>=</sup> selectivity,
and low activity. For the unpromoted catalyst and the catalysts promoted
by Ce and La, Co<sub>2</sub>C nanospheres are also obtained, with
catalytic performance similar to that of the Mn/Co catalyst prepared
via impregnation. Due to the high stability of the Co<sub>2</sub>AlO<sub><i>x</i></sub> composite oxide, no Co<sub>2</sub>C phase
can be formed for the catalyst promoted by Al
Disrupted Functional Brain Connectome in Individuals at Risk for Alzheimer's Disease
Background: Alzheimer's disease disrupts the topological architecture of whole-brain connectivity (i.e., the connectome); however, whether this disruption is present in amnestic mild cognitive impairment (aMCI), the prodromal stage of Alzheimer's disease, remains largely unknown. Methods: We employed resting-state functional magnetic resonance imaging and graph theory approaches to systematically investigate the topological organization of the functional connectome of 37 patients with aMCI and 47 healthy control subjects. Frequency-dependent brain networks were derived from wavelet-based correlations of both high-and low-resolution parcellation units. Results: In the frequency interval .031-.063 Hz, the aMCI patients showed an overall decreased functional connectivity of their brain connectome compared with control subjects. Further graph theory analyses of this frequency band revealed an increased path length of the connectome in the aMCI group. Moreover, the disease targeted several key nodes predominantly in the default-mode regions and key links primarily in the intramodule connections within the default-mode network and the intermodule connections among different functional systems. Intriguingly, the topological aberrations correlated with the patients' memory performance and differentiated individuals with aMCI from healthy elderly individuals with a sensitivity of 86.5% and a specificity of 85.1%. Finally, we demonstrated a high reproducibility of our findings across different large-scale parcellation schemes and validated the test-retest reliability of our network-based approaches. Conclusions: This study demonstrates a disruption of whole-brain topological organization of the functional connectome in aMCI. Our finding provides novel insights into the pathophysiological mechanism of aMCI and highlights the potential for using connectome-based metrics as a disease biomarker
Subjective Cognitive Decline: Mapping Functional and Structural Brain ChangesāA Combined Resting-State Functional and Structural MR Imaging Study
Effects of Sodium on the Catalytic Performance of CoMn Catalysts for FischerāTropsch to Olefin Reactions
The
effects of a sodium (Na) promoter on the catalytic performance
of cobalt-manganese (CoMn) catalysts for FischerāTropsch to
olefin (FTO) reactions were investigated. For the sample without Na,
Co<sup>0</sup> was found to be the active phase for the traditional
Co-based FischerāTropsch reaction with low CO<sub>2</sub> selectivity.
The olefin/paraffin (O/P) ratio was found to be low with a C<sub>2ā4</sub><sup>=</sup> selectivity of only 15.4 C%. However, with the addition
of Na, cobalt carbide (Co<sub>2</sub>C) quadrangular nanoprisms with
the (101) and (020) facets exposed were formed. The Co<sub>2</sub>C nanoprisms displayed a high C<sub>2ā4</sub><sup>=</sup> selectivity
(54.2 C%) as well as a low methane selectivity (5.9 C%) under mild
reaction conditions. The O/P ratio for C<sub>2ā4</sub> reached
23.9, and the product distribution deviated greatly from the classical
AndersonāSchulzāFlory (ASF) distribution. Co<sub>2</sub>C nanoprisms were considered to be an effective FTO active phase
with strong facet effects. The Na promoter played a key role in the
evolution of the FTO catalysts. The addition of Na, which acted as
an electronic donor to cobalt, resulted in stronger CO adsorption
and enhanced CO dissociation, which also benefited the formation of
the Co<sub>2</sub>C phase, leading to highly stable and active catalysts.
The effects of other alkali promoters were also studied, and only
the K promoter had an effect similar to that of Na on the CoMn catalysts
for promoting the FTO reaction