Depicting urban boundaries from a mobility network of spatial interactions: A case study of Great Britain with geo-located Twitter data

Existing urban boundaries are usually defined by government agencies for administrative, economic, and political purposes. Defining urban boundaries that consider socio-economic relationships and citizen commute patterns is important for many aspects of urban and regional planning. In this paper, we describe a method to delineate urban boundaries based upon human interactions with physical space inferred from social media. Specifically, we depicted the urban boundaries of Great Britain using a mobility network of Twitter user spatial interactions, which was inferred from over 69 million geo-located tweets. We define the non-administrative anthropographic boundaries in a hierarchical fashion based on different physical movement ranges of users derived from the collective mobility patterns of Twitter users in Great Britain. The results of strongly connected urban regions in the form of communities in the network space yield geographically cohesive, non-overlapping urban areas, which provide a clear delineation of the non-administrative anthropographic urban boundaries of Great Britain. The method was applied to both national (Great Britain) and municipal scales (the London metropolis). While our results corresponded well with the administrative boundaries, many unexpected and interesting boundaries were identified. Importantly, as the depicted urban boundaries exhibited a strong instance of spatial proximity, we employed a gravity model to understand the distance decay effects in shaping the delineated urban boundaries. The model explains how geographical distances found in the mobility patterns affect the interaction intensity among different non-administrative anthropographic urban areas, which provides new insights into human spatial interactions with urban space.Comment: 32 pages, 7 figures, International Journal of Geographic Information Scienc

Cooperative "folding transition" in the sequence space facilitates function-driven evolution of protein families

In the protein sequence space, natural proteins form clusters of families which are characterized by their unique native folds whereas the great majority of random polypeptides are neither clustered nor foldable to unique structures. Since a given polypeptide can be either foldable or unfoldable, a kind of "folding transition" is expected at the boundary of a protein family in the sequence space. By Monte Carlo simulations of a statistical mechanical model of protein sequence alignment that coherently incorporates both short-range and long-range interactions as well as variable-length insertions to reproduce the statistics of the multiple sequence alignment of a given protein family, we demonstrate the existence of such transition between natural-like sequences and random sequences in the sequence subspaces for 15 domain families of various folds. The transition was found to be highly cooperative and two-state-like. Furthermore, enforcing or suppressing consensus residues on a few of the well-conserved sites enhanced or diminished, respectively, the natural-like pattern formation over the entire sequence. In most families, the key sites included ligand binding sites. These results suggest some selective pressure on the key residues, such as ligand binding activity, may cooperatively facilitate the emergence of a protein family during evolution. From a more practical aspect, the present results highlight an essential role of long-range effects in precisely defining protein families, which are absent in conventional sequence models.Comment: 13 pages, 7 figures, 2 tables (a new subsection added

Outlier Detection and Comparison of Origin-Destination Flows Using Data Depth

Advances in location-aware technology have resulted in massive trajectory data. Origin-destination (OD) trajectories provide rich information on urban flow and transport demand. This study describes a new method for detecting OD flows outliers and conducting hypothesis testing between two OD flow datasets in terms of the variations of spatial extent, that is, spread. The proposed method is based on data depth, which measures the centrality and outlyingness of a point with respect to a given dataset in R^d. Based on the center-outward ordering property, the proposed method analyzes the underlying characteristics of OD flows, such as location, outlyingness, and spread. The ability of the method to detect OD anomalies is compared with that of the Mahalanobis distance approach, and an F-test is used to verify the difference in scale. Empirical evaluation has demonstrated that our method effectively identifies OD flows outliers in an interactive way. Furthermore, the method can provide new perspectives such as spatial extent by considering the overall structure of data when comparing two different OD flows in terms of scale

An empirical analysis of the profitability of Chinese Banks

Abstract Employing the Stochastic Frontier Approach (SFA) and the System Generalised Method of Moment (SGMM), this paper aims to estimate the determinants of dynamic profitability of 210 Chinese commercial banks in the time period from 2013 to 2017. Among the two estimation techniques in this paper, SFA model is applied to obtain the cost efficiency scores of the sample banks which are used in the subsequent study, and the SGMM model is mainly discussed in this the performance study. Indicators at micro, meso and macro levels are selected according to provisions literature and the Return on Average Assets (ROAA) of a bank is used as the measurement of banks profitability. The results show that multiple determinants are influencing banks profitability at the same time. The ratio of Loan to Total Assets, Equity to Total Assets, GDP Growth Rate and Inflation Rate are found to have significant positive relationship with ROAA, while the ratio of Loan Loss Provisions to Total Assets, Loan Reserves to Gross Loans, The ratio of Net Loans to Deposits plus Short-Term Funding and the cost-to-Income ratio and are found to have negative relationship with ROAA. However, several indicators as Bank Size, Z-Score, Unemployed Rate and Cost Efficiency score are shown to have insignificant influence on a bank’s profitability in this case

Induction of Changes Over time in the Rat Proximal Femur Following Ovariectomy: A Model with Clinical Implications

The menopause-related expansion of the proximal femoral marrow cavity is thought to have implications  for the long-term cohesion of hip prostheses. This theory would be further strengthened if there was evidence  to show that the expansion of the proximal femur marrow cavity takes place after the occurrence of  a femoral neck fracture, which, it is often recommended, should be fixed with a hip prosthesis. But till now,  the temporal relationship between those two osteoporotic-related changes has not been checked carefully.  The objective of the current study was to examine the temporal relationship between the marrow cavity  expansion of the proximal femur and the biomechanical deterioration of the femoral neck in a rat model.  To do so, a cross-sectional study with multiple time points was carried out on 6-month old Sprague-Dawley  rats, which were ovariectomized or sham-operated (as controls). The biomechanical properties of the femur  neck and geometrical parameters of the femur shaft were evaluated at 0, 3, 6, 9, 12, 15, 18, and 21 weeks  postoperatively, with special reference to the timescale of the observed changes. We found that the maximum  load of the femoral neck in ovariectomized rats could bear decreased significantly compared, to that  of controls, at 9 weeks postoperatively (p=0.03), while the marrow cavity of the proximal femur in ovariectomized  rats turned out to be significantly enlarged at 15 weeks postoperatively (p=0.04). Conclusion: Our  result demonstrated that the osteoporosis-related marrow-enlarged posterior led to the collapse of femoral  neck strength. If the change in postmenopausal women is analogous to that in ovariectomized rats, the  menopause-related marrow cavity expansion would be a risk factor for the longevity of hip prostheses.