Hierarchical Aggregation for Numerical Data under Local Differential Privacy.

The proposal of local differential privacy solves the problem that the data collector must be trusted in centralized differential privacy models. The statistical analysis of numerical data under local differential privacy has been widely studied by many scholars. However, in real-world scenarios, numerical data from the same category but in different ranges frequently require different levels of privacy protection. We propose a hierarchical aggregation framework for numerical data under local differential privacy. In this framework, the privacy data in different ranges are assigned different privacy levels and then disturbed hierarchically and locally. After receiving users' data, the aggregator perturbs the privacy data again to convert the low-level data into high-level data to increase the privacy data at each privacy level so as to improve the accuracy of the statistical analysis. Through theoretical analysis, it was proved that this framework meets the requirements of local differential privacy and that its final mean estimation result is unbiased. The proposed framework is combined with mini-batch stochastic gradient descent to complete the linear regression task. Sufficient experiments both on synthetic datasets and real datasets show that the framework has a higher accuracy than the existing methods in both mean estimation and mini-batch stochastic gradient descent experiments.

Establishment and characterization of two fetal fibroblast cell lines from the yak.

The objective of this work was to not only establish two fetal fibroblast cell lines from yak lung and ear tissue using a primary explant technique and cell cryogenic preservation technology but also check for their quality and biological characteristics. The cells showed typical morphologic characteristics of fibrous and long spindle appearance. Outgrowth of fibroblast-like cells from the lung and ear explants was around 2 and 3 d, and reaching 90% confluence level was in the ninth day and the thirteenth day, respectively. Biological analysis showed that the average viability of the lung fibroblast cells (ear fibroblast cells) was 97.5% (95.0%) before freezing and 91.0% (89.5%) after thawing. Analysis of the growth of the fifth passage culture revealed an "S"-shaped growth curve with the population doubling times of 30 h for lung fibroblast cell line and 35 h for ear fibroblast cell line. Karyotyping indicated the chromosome number of yak was 2n = 60, comprising 29 pairs of autosomes and one pair of sex chromosomes (XY). All somatic chromosomes were telocentric autosomes except that the two sex chromosomes were submetacentric. Assays for bacteria, fungi, and mycoplasmas were negative. Immunocytochemical staining showed that the cells were positive for the expression of vimentin and negative for the expression of cytokeratin. In conclusion, two yak fetal fibroblast cell lines (YFLF and YFEF) from lung and ear explants are successfully established in culture. It will not only preserve the genetic resources of yaks at the cellular level but also provide valuable materials for somatic cell cloning and transgenic research.