k-center问题的算法研究综述

k-center问题是设施选址的基础问题,同样是NP难问题,在分配、紧急服务等领域也有着实际的应用。随着问题规模的扩大,原有的算法已不再适用,需要进一步优化或者改进。为了找到求解该问题的高效算法,对现有算法进行研究。对各类求解k-center问题的算法进行梳理,将求解算法划分为精确算法、启发式算法、元启发式算法、近似算法等,从算法原理、改进思路、性能和精度等方面进行对比综述。精确算法在求解小规模k-center问题时可在多项式时间内得到最优解,但是算法效率低,不适用于大规模问题;启发式算法可以在多项式时间内给出相对最优解,但是没有理论保证,无法衡量与最优解的关系;元启发式算法可根据对目前存在的智能优化算法进行改进,给出相对最优解,但是解的质量无法保证;利用近似算法得到的解具有近似比保证,有较大的理论研究价值,但是实用价值较弱。目前求解k-center问题的元启发式算法已取得一定的研究成果,但是在求解时间、求解规模、算法效率等方面仍待突破,这将是未来k-center问题的研究重点。

Cortical hem signaling center: functions, development, and potential implications for evolution and brain disorders

Development of the telencephalon relies upon several signaling centers-localized cellular populations that supply secreted factors to pattern the cortical neuroepithelium.One such signaling center is the cortical hem,which arises during embryonic development at the telencephalic dorsal midline,adjacent to the choroid plexus and hippocampal primordium(Figure 1A).While the cortical hem has also been described in reptiles and birds,most of our knowledge about the developmental roles of the cortical hem is derived from the analysis in mice.The cortical hem produces several types of secreted molecules,including wingless-related integration site(Wnt)and bone morphogenetic(Bmp)proteins.The cortical hem is particularly important for the development of the hippocampus,which is involved in learning and memory,and the neocortex,which is the most complex brain region that mediates multiple types of behavior and higher cognitive functions(Mangale et al.,2008;Dal-Valle-Anton and Borrell,2022).

Examining the Burden Reduction Policy for Primary and Secondary School Teachers in China:A Framework Analysis Centered on the Rational Selection of Institutional Doctrine

The“burden reduction”policy aims to reduce the workload of primary and secondary school teachers to alleviate their burdens.While it has improved the quality of teachers,implementation challenges still exist.This study utilizes rational choice institutionalism and Ostrom’s institutional analysis and development framework to examine the policy.By considering the preferences of the Ministry of Education,local governments,schools,and teachers,it explores interactions and outcomes,identifies challenges,and provides policy suggestions.

构建适用于高职教育的“Learner-centered”教学模式研究

当前,高职计算机学科的课堂存在着师生互动性欠缺,学生自主学习意识薄弱等明显的问题。在教育教学改革新动向、在线教育蓬勃发展新趋势的背景下,为了解决高职教育教学中存在的显著问题,我们提倡并研究"Learner Centered"教学模式.通过在相关计算机课程中的具体实施和问卷分析,总结"Learner-centered"教学模式对于高职教育的优势和可行性。

Chemical Bonds between Charged Atoms in the Even-Odd Rule and a Limitation to Eight Covalent Bonds per Atom in Centered-Cubic and Single Face-Centered-Cubic Crystals

A crystal is a highly organized arrangement of atoms in a solid, wherein a unit cell is periodically repeated to form the crystal pattern. A unit cell is composed of atoms that are connected to some of their first neighbors by chemical bonds. A recent rule, entitled the even-odd rule, introduced a new way to calculate the number of covalent bonds around an atom. It states that around an uncharged atom, the number of bonds and the number of electrons have the same parity. In the case of a charged atom on the contrary, both numbers have different parity. The aim of the present paper is to challenge the even-odd rule on chemical bonds in well-known crystal structures. According to the rule, atoms are supposed to be bonded exclusively through single-covalent bonds. A distinctive criterion, only applicable to crystals, states that atoms cannot build more than 8 chemical bonds, as opposed to the classical model, where each atom in a crystal is connected to every first neighbor without limitation. Electrical charges can be assigned to specific atoms in order to compensate for extra or missing bonds. More specifically the article considers di-atomic body-centered-cubic, tetra-atomic and dodeca-atomic single-face-centered-cubic crystals. In body-centered crystals, atoms are interconnected by 8 covalent bonds. In face-centered crystal, the unit cell contains 4 or 12 atoms. For di-element crystals, the total number of bonds for both elements is found to be identical. The neutrality of the unit cell is obtained with an opposite charge on the nearest or second-nearest neighbor. To conclude, the even-odd rule is applicable to a wide number of compounds in known cubic structures and the number of chemical bonds per atom is not related to the valence of the elements in the periodic table.

Family Centered Care versus Child Centered Care: The Malawi Context

Family Centered care is a model that is practiced and encouraged in child health care. It considers family as partners and collaborators in care of children. It aims at involving family in all aspects of child care. Family centered care also mentions involvement of child. However, emphasis is given more on family than child and does not take into account the older child’s capacity for independent decision making and right to privacy. As such, child’s needs are missed out. With child centered care, children are involved and supported at all levels of care based on their age and developmental stage. This paper aims to stress the importance of involving children within family centered care. Involving children in their care, makes them feel less threatened by the health care professional and their self esteem is promoted. Currently, no studies have been identified in Malawi that demonstrates full partnership between the family, child and the nurse. Furthermore, Family Centered Care and Child Centered Care as models are not fully practiced. It is therefore important to practice both family and child centered care in child health care if the needs of both family and children are to be addressed concurrently.

Comparison of visual effects of FS-LASIK for myopia centered on the coaxially sighted corneal light reflex or the line of sight

AIM：To compare visual quality after femtosecond laser in situ keratomileusis（FS-LASIK）,between the coaxially sighted corneal light reflex（CSCLR） group and conventional ablation line of sight（LOS） group.METHODS：In total,243 eyes（122 patients） were treated with centration on the CSCLR（visual axis） and 238 eyes（119 patients） treated with centration on the pupil center（LOS）.Postoperative outcomes [uncorrected visual acuity（UCVA）,best spectacle-corrected visual acuity（BSCVA）],safety index,efficacy index,refractive outcome,ablation center distance from the visual axis,corneal high-order aberrations,subjective discomfort glare and shadowing incidence rate,and contrast sensitivity at 1,3,and 6mo were measured and compared.RESULTS：The mean age was 27.77±7.1y in the CSCLR group and 26.03±7.70 y in the LOS group.Preoperatively,the manifest refraction spherical equivalent（MRSE） was-6.68±2.60 D in the CSCLR group and-6.65±2.68 D in the LOS group.The postoperative UCVA,BSCVA,MRSE（-0.03±0.263 D in the CSCLR group,-0.05±0.265 D in the LOS group）,efficacy index（1.04,1.03）,and safety index（1.09,1.08） were not significantly different between the groups（all P〉0.05）.In total,3% lost one line and more of BSCVA in the CSCLR group,as 9% in the LOS group postoperatively（P〈0.05）.The ablation center deviation was 0.20±0.15 mm from the visual axis（Pentacam system default setting;range,0-0.75 mm） in the CSCLR group,and 0.43±0.22 mm（range,0-1.32 mm） in the LOS group（P〈0.0001）.Statistically significant greater augmentationof total corneal higher-order aberrations（0.15±0.10 μm and 0.20±0.12 μm respectively,P=0.03） and vertical and horizontal coma（P〈0.0001） were noted in the LOS group.Subjective discomfort glare and shadowing incidence rates were 8.59% and 17.5% in the CSCLR and LOS groups,respectively（P〈0.05）.The 1-month postoperative contrast sensitivity visual acuity in the CSCLR group was significantly higher than that in the LOS group on contrast（100%,25%,10%） with a dark background,but there was no significant difference between the groups at 3 or 6m.CONCLUSION：Myopic LASIK centered on the CSCLR achieves significantly lower induction of loss of BSCVA,corneal high-order aberrations,and lower risk of subjective discomfort glare and shadowing,and lower decline in early contrast sensitivity by comparison with centration on the LOS,giving advantages in visual quality postoperatively.

Application of Student-centered Learning Approach to English Listening and Speaking Class in Vocational Schools

Student-centered learning approach is focused on the students' demands and interests.Applying student-centered approach puts forward higher requirement to English teachers.This article first analyzes the theory of student-centered learning approach and compares teacher-centered approach with it.Based on the research information and teaching experience,the author summarizes four strategies about how to apply student-centered learning approach to English listening and speaking class in vocational schools.

Fractional Optical Solitons and Fractional Noether’s Theorem with Ortigueira’s Centered Derivatives

This paper shows that the centered fractional derivatives introduced by Manuel Duarte Ortigueira in 2006 are useful in the description of optical solitons. It is shown that we can construct a fractional extension of the nonlinear Schrödinger (NLS) equation which incorporates Ortigueira’s derivatives and has soliton solutions. It is also shown that this fractional NLS equation has a Lagrangian density and can be derived from a variational principle. Finally, a fractional extension of Noether’s theorem is formulated to determine the conserved quantities associated to the invariances of the action integral under infinitesimal transformations.

Exploration on the Construction of "Student-centered" Professional Three-Dimensional Practical Teaching System

Talent cultivation is the primary task of universities.Local general undergraduate colleges and universities should adhere to the basic guidelines of systematization,practicality and integration,continuously explore the concept of"studentcentered"talent cultivation,and build a threedimensional practical teaching system from three aspects:strengthening the planning and design of the three-dimensional practical teaching system;building an internal and external practical teaching platform;and improving the evaluation and guarantee system of practical teaching quality.The system of practical teaching quality evaluation and guarantee is improved.In order to improve the cultivation ability of applied talents in all aspects.

Centered simple waves for the two-dimensional pseudo-steady isothermal ?ow around a convex corner

The two-dimensional(2D) pseudo-steady isothermal flow, which is isentropic and irrotational, around a convex corner is studied. The self-similar solutions for the supersonic flow around the convex corner are constructed, where the properties of the centered simple wave are used for the 2D isentropic irrotational pseudo-steady Euler equations. The geometric procedures of the center simple waves are given. It is proven that the supersonic flow turns the convex corner by an incomplete centered expansion wave or an incomplete centered compression wave, depending on the conditions of the downstream state.

On the Learner-Centered Teaching Approach——The Reflection Getting from New College English By ZheJiang University

This paper first focuses on a brief evaluation of the teacher-centered and the learner-centered methodologies and the relevant result and the necessity for changing. Secondly ,it represents the practical ways of teaching based on the learner-centered approach in classrooms to show how students' initiative is given .Thirdly , it presents the guidance for fellow teachers and students in group activities .The author of the paper believes that getting students started is the initial step towards active learning and fruitful teaching. It is proposed that efforts made to get students involved should focus not only on forms of activities but also on their contents , skill integration and establishing cooperative relationships between teachers and students or among students.

CYCLIC DEFORMATION OF FACE CENTERED CUBIC CRYSTALS AND ITS DISLOCATION INTERACTION MODEL——Ⅱ.DISLOCATION INTERACTION MODEL OF CYCLIC DEFORMATION

A dislocation interaction model has been proposed for cyclic deformation of fcc crystals.Ac- cording to this model,cyclic stress-strain responses and saturation dislocation structures of a crystal are associated with the modes and intensities of dislocation interactions between slip systems active in the crystal; and,hence,may be predicted by the location of its tensile axis in the crystallographic triangle.This model has successfully explained the different behaviours of double-slip crystals and multi-slip behaviours of some crystals with orientations usually con- sidered as single-slip ones.

A Local Property of Hausdorff Centered Measure of Self-Similar Sets

We analyze the local behavior of the Hausdorff centered measure for self- similar sets. If E is a self-similar set satisfying the open set condition, thenC^s（E∩B（x,r））≤（2r）^sfor all x ∈ E and r〉 0, where Cs denotes the s-dimensional Hausdorff centered measure. The above inequality is used to obtain the upper bound of the Hausdorff centered measure. As the applications of above inequality, We obtained the upper bound of the Hausdorff centered measure for some self-similar sets with Hausdorff dimension equal to 1, and prove that the upper bound reach the exact Hausdorff centered measure.

基于WGAN-GP和Mean Teacher的WiFi使能跨域人体行为识别

人体行为识别(Human Activity Recognition,HAR)是当前众多研究工作的基石,对于推动人机交互和智能数字化转型具有巨大潜力。由于目标域样本较难采集,现有方法在跨域识别方面表现不佳。为解决这一问题,提出一种新的WiFi使能跨域HAR方法,从WiFi信号中获取信道状态信息(Channel State Information,CSI)并转化为图像,在基于Wasserstein距离和梯度的生成对抗网络(Wasserstein Generative Adversarial Network with Gradient Penalty,WGAN-GP)中引入双判别器,通过与源域样本和单目标域样本特征联合对抗,生成同时带有双域特征的虚拟样本。该方法还结合基于Mean Teacher的半监督学习设计识别分类(Recognition and Classification,RC)模块,通过对有标记样本与无标记样本分别构造损失函数,进行整体一致性损失的评估,实现对目标域样本的识别。实验结果证明了所提方法能够在减轻目标域样本采集压力的同时,实现较高的检测精度,在手势与动作的数据集上测试准确率分别达到92.71%和86.65%。

Barriers to the Acceptance of Tuberculosis Preventive Treatment:A Multicenter Cross-sectional Study in China

Objective We aimed to understand the willingness and barriers to the acceptance of tuberculosis(TB)preventive treatment(TPT)among people with latent TB infection(LTBI)in China.Methods A multicenter cross-sectional study was conducted from May 18,2023 to December 31,2023 across 10 counties in China.According to a national technical guide,we included healthcare workers,students,teachers,and others occupations aged 15-65 years as our research participants.Results Overall,17.0%(183/1,077)of participants accepted TPT.There were statistically significant differences in the acceptance rate of TPT among different sexes,ages,educational levels,and occupations(P<0.05).The main barriers to TPT acceptance were misconceptions that it had uncertain effects on prevention(57.8%,517/894),and concerns about side effects(32.7%,292/894).Conclusion An enhanced and comprehensive understanding of LTBI and TPT among people with LTBI is vital to further expand TPT in China.Moreover,targeted policies need to be developed to address barriers faced by different groups of people.

A Monte Carlo Simulation of a Monomer Dimer CO-O2 Catalytic Reaction on the Surface and Subsurface of a Face-centered Cubic Lattice

The presence of oxygen in the subsurface in monomer-dimer reactions(CO-O_(2)and NO-CO)is observed experimentally.The effect of subsurface oxygen on a CO-O_(2)catalytic reaction on a face-centered cubic(FCC)lattice is studied using Monte Carlo simulation.The effect of adding subsurface neighbours on the phase diagram is also extensively explored.It is observed that the subsurface oxygen totally eliminates the typical second order phase transition.It is also shown that the introduction of the diffusion of O atoms and the subsurface of the FCC lattice shifts the single transition point towards the stoichiometric ratio.

Design of space-centered interaction using invisible and intangible spatial inputs

In this paper,we investigate methodologies to improve direct-touch interaction on invisible and intangible spatial input.We firstly discuss about the motive of looking for a new input method for whole body interaction and how it can be meaningful.We also describe the role that can play spatial interaction to improve the freedom of interaction for a user.We propose a method of spatial centered interaction using invisible and intangible spatial inputs.However,given their lack of tactile feedback and visual representation,direct touch interaction on such input can be confused.In order to make a step toward understanding causes and solutions for such phenomena,we made 2 user experiments.In the first one,we test 5 setups of helper that provide information of the location of the input by constraining the dimension it is located at.The results show that using marker on the ground and a relationship with the height of the user’s body improve significantly the locative task.In the second experiment,we create a dancing game using invisible and intangible spatial inputs and we stress the results obtained in the first experiment within this cognitively demanding context.Results show that the same setup of helper is still providing very good results in that context.

对流扩散方程的迎风Cell-centered混合元方法

讨论对流扩散方程的一种迎风Cell-centered混合元方法,在不同的矩形网格剖分下,分别用常量浓度元与常量通量元逼近原问题的解,得到了浓度与通量的一阶L2模误差估计,并通过数值算例验证了理论分析结果的正确性。

Differentiation between two healthcare concepts:Person-centered and patient-centered care

1.Background Engel's biopsychosocial model,which was constructed in 1977,was considered a momentous breakthrough from the traditional biomedical model of medicine that regards the person as a disease-carrier requiring diagnosis and treatment[1]towards recognition of the whole person and furnish customized care.This model argues that health should not be considered solely on biological factors but on a combination of biological,psychological,and social factors[2].This idea of considering individuals as a whole and respecting their rights to self-determination has led to a shift in the care model from disease-centered care to patient-centered or person-centered care.The latter two care models are both abbreviated as PCC.Ensuring that people are involved in and central to the healthcare process is now recognized as a key component in developing high-quality care.Studies have revealed that both concepts of care can help improve people's health condition and lower health service burdens.Thus,countries and healthcare organizations have been paying close attention to the patients'concerns.The National Health Service in England has made person-centered care as one of its seven core principles[3].