식품 중 보존료의 일제분석에 관한 연구

정진일,민승식,노미정,박유신,남궁석 한국법과학회 2002 한국법과학회지 Vol.3 No.1

As the use of preservatives in foods has been increased, the misuse and overuse of preservatives are occasionally occurred. As the variety of food has risen, it is necessary to establish the screening method to determine preservatives in various foods. In this study, benzoic acid, sorbic acid, methyl p-hydroxybenzoate, ethyl p-hydroxybenzoate, i-propyl p-hydroxybenzoate, n-butyl p-hydroxybenzoate were analyzed by TLC and HPLC. In order to determine the recoveries from food, these preservatives were spiked into foods. As a result, solvent systems of 8:2:0.45:0.05 and 12:2:0.45:0.05 of pentane:acetic acid:chloroform:ethanol were appropriate for TLC analysis of preservatives. All preservatives were well resolved with solvent system of 2% ammonium acetate in 2.5% acetic acid:methanol (90/10~10/90) by HPLC. Direct extraction of preservatives from food proved to be more proper than distillation and extraction method. The recoveries by direct extraction method showed 93.7~104.6% of preservatives studied.

Al-Mg합금(Al-5wt%Mg-3wt%Zn-1wt%Mn)의 T6 열처리에 따른 미세조직 및 기계적 특성변화

유정훈,신기삼,허성강,김정민 국립7개대학공동논문집간행위원회 2005 공업기술연구 Vol.5 No.-

Al-Mg base alloys are attractive for aircraft. automobile and leisure applications because of their properties of low density, high intensity and wear resistance. The effect of Zn and Mn on the properties was studied in an Al-Mg base alloy. After T6 heat-treatment, the change of the microstructure and mechanical property was examined. Our investigations show that after T6 heat-treatment, the elongation was improved. The microstructures are investigated by TEM, which shows that the size of Al6Mn, Al57Mn12 phase is 100~500nm, and it also appears presence of the very small size MgZn₂ phase about 30nm.

쿠싱증후군 환자에서 당 대사 이상 정도에 따른 인슐린 감수성과 인슐린 저항성의 변화

정인경,김성훈,정재훈,민용기,이명식,이문규,유형준,안규정,노정현,김동준,김광원 대한내분비학회 2003 Endocrinology and metabolism Vol.18 No.4

연구배경 당질 코르티코이드는 당 대사에 매우 중요한 호르몬으로 내인성 당질 코르티코이드 과다상태인 쿠싱증후군에서는 말초조직에서 인슐린 저항이 증가하고 이를 보상하고자 인슐린 분비의 증가로 고인슐린혈증이 동반된다고 보고되고 있다. 하지만 생체 내에서와 달리 시험관내에서는 췌도세포에 당질 코르티코이드를 장시간 처리하면, 인슐린 분비 및 생합성이직접적으로 억제됨이 확인된 바 있어 쿠싱증후군 환자에서 당뇨병의 원인으로는 아마도 말초조직에서 증가된 인슐린 저항성 뿐 아니라 이를 충분히 보상하지 못하는 췌장에서의 인슐린 분비 저하가 같이 동반되어있지 않을까 하는 가설을 세우게 되었고, 아직까지 당질코르티코이드가 당대사 이상을 일으키는 기전에 대해 쿠싱증후군을 당대사 정도에 따라 인슐린 감수성과 분비능을 분석한 연구는 없었기에 이를 알아보고자 하였다. 방법: 삼성서울병원에서 쿠싱증후군으로 진단 받은 환자 15명을 대상으로 하였다. 이에 대한 대조군으로는 쿠싱증후군 환자와 같은 성별 그리고 체질량지수를 갖은 15명의 건강한 성인을 대상으로 비교 하였다 쿠싱증후군 환자를 대상으로 경구당부하 검사를 통해 당대사 정도를 정상군, 내당능장애군, 그리고 당뇨병군으로 나눈 후 정맥 당부하 검사를 시행하여 각군의 인슐린 저항성과 인슐린 분비능의 지표를 비교하고, 수술 후 쿠싱증후군이 완치된 상태에서 수술 전후의 당대사 지표의 변화를 조사하였다. 결과: 1) 쿠싱증후군 환자 중 정상인은 20%, 내당능 장애는 27%, 그리고 당뇨병은 53%였다. 체질량지수, 나이, 그리고 발병 기간은 세 군간에 의미 있는 차이가 없었으나, 24시간 소변검사의 코르티솔 농도는 당뇨병군에서 의미있게 높았다. 2) 정맥당부하 검사 결과, 인슐린 감수성 지표인 Sl는쿠싱증추린」서 1.58±0.10[×10^(-4)(min^(-1)(μU/mL)^(-1)]로 정상 대조군의 3.37±0.49[×10^(-4)(min^(-1)(μU/mL)^(-1)]에 비해 의미있게 낮았으나(P=0.024), 쿠싱증후군 환자 중 NGT, IGT, DM 군간에 서로 통계적인 차이는 없었다. 3) SG는 정상 대조군과 쿠싱증후군 환자간에는 의미있는 차이가 없었고, 쿠싱 증후군에 있어서 당대사가 악화될수록 감소하는 경향을 보였으나 의미있는 차이는 없었다. 4) 인슐린 분비능의 지표인 AIRg는 정상인에 비해 전체 쿠싱증후군 환자의 경우 증가하는 경향을 보였으나 의미있는 차이는 없었다. 하지만 쿠싱증후군 환자중에서 당대사 상태에 따라 NGT군은 1299 (1297∼1310)(mu/g/min ×10^(-2))로 정상 대조군(368.9±98.6[mu/g/min ×10^(-2)]) 보다도 의미있게 높았고, DM군{202.2 (91.1~371.4) [mu/g/min ×10^(-2)}은 NGT군에 비해 의미있게 낮았다(P=0.0031). 5) 15명중 현재 완치 상태에 있는 6명에 대해 수술전과 후로 비교하였다. 수술 전 당대사 상태가 1명은정상, 1명은 내당능 장애, 그리고 4명은 당뇨병이었으나 수술 후 시행한 경구 당부하 검사상 모두 정상 당대사 상태를 보였다. 6) 수술 후 완치된 환자 6명에 있어 인슐린 감수성지표인 Sl는 수술전에 중앙값이 1.22[×10^(-4)(min^(-1)(μU/mL)^(-1)]로 대조군에 비해 의미있게 감고』어 있었으나(p.0.05), 수술후 10.95 [×10^(-4)(min^(-1)(μU/mL)^(-1)]로 정상 수준으로 회복되었고(P=0.0022), 인슐린 분비능을 나타내는 AIRg [mu/g/min ×10^(-2)] 값도 정상수준으로 회복되었다. 특히 인슐린 분비능의 회복양상은 혈당농도에 따라 판이하게 나타나서, 정상과 내당능장애 상태에 있던 2명은 수술전에 1201 [mu/g/min ×10^(-2)]로 증가되어 있던 AIRg 값이 수술 후 정상 수준으로 감소하였고, 수술 전에 당뇨병 상태에 있던 4명의 경우 245.9 [mu/g/min ×10^(-2)]로 인슐린 분비능이 감고il어 있었는데 이들은 수술 후 모두 정상 수준으로 증가되었다 (P=0.0286). 결론: 쿠싱증후군 환자에서 당대사 이상은 80%로 높은 유병률을 보였다. 모든 쿠싱증후군환자에서 인슐린 감수성은 정상인에 비해 저하되어 있어 말초조직의 인슐린 저항이 선행됨을 시사하며, 인슐린 분비능은 당대사의 정도에 따라 다르게 나타났는데, 정상 당대사군에서는 인슐린의 저항성을 극복할 만큼 정상 대조군보다 더 많은 양의 인슐린 분비를 하다가 고코르티솔혈증이 심할수록 인슐린 분비능의 감소로 당뇨병으로 진행됨을 확인할 수 있었고, 이런 인슐린 저항성과 인슐린 분비장애는 수술 후 다시 회복되는 가역적인변화를 보였다. Background: Glucocorticoid plays an important role in the control of carbohydrate metabolism. Patients with Cushing's syndrome have been reported to have an increased incidence of carbohydrate intolerance due to peripheral insulin resistance and hyperinsulinemia, although the exact incidence and nature of this disorder have remained unclear. Few results have been published about insulin resistance and insulin secretion according to the level of glucose concentration, or about the reversibility of such defects in patients with Cushing's syndrome. Methods: To assess the effect of glucocorticoid on the insulin sensitivity and insulin secretion in Cushing's syndrome, 15 patients with Cushing's syndrome were classified into 3 groups (normal glucose tolerance: NGT, impaired glucose tolerance: IGT, diabetes: DM) according to the degree of glucose tolerance based on the oral glucose tolerance test (OGTT). Insulin modified, frequently sampled, intravenous glucose tolerance test (FSIGT) was performed before and after curative surgery on these patients and on 15 healthy control subjects. Data were evaluated by non-parametric statistical analysis. Results: 1) Among the 15 patients with Cushing's syndrome, 3 (20%) were NGT, 4 (27%) IGT, and 8 (53%) DM, based on OGTT. Twenty-four hour urinary free cortisol (UFC) was significantly higher in the DM group. 2) Insulin sensitivity index (SI) of Cushing's syndrome was significantly lower than that of the control group p=0.0024), but was not significantly different among the three Cushing's syndrome groups of NGT, IGT and DM. 3) Glucose mediated glucose disposal (SG) (Ed- confirm this abbreviation; it does not seem to match the definition) of Cushing's syndrome was not significantly different from that of the control group. 4) Insulin secretion (AIRg) of Cushing's syndrome tended to be high, but it was not significantly different from that of control. However, according to the level of glucose concentration there was significant difference in AlRg among the three Cushing's syndrome groups p=0.0031); AIRg of DM was significantly lower than that of NGT. 5) After surgical treatment, parameters of insulin sensitivity and insulin secretion were normalized in 6 cured patients; 1 with NGT, 1 with IGT, and 4 with DM, preoperatively. Median SI of all 6 patients was significantly improved up to the normal range postoperatively p=0.0022). Median AIRg of these 6 patients was balanced around that of normal control postoperatively p=0.0286). Conclusion: Eighty percent of patients with Cushing's syndrome had abnormality of carbohydrate metabolism. Insulin sensitivity was significantly decreased in Cushing's syndrome. Insulin secretion was significantly higher only in the NGT and IGT groups of Cushing's syndrome. As the hypercortisolemia is exacerbated, insulin secretion is significantly decreased and causes DM, suggesting that glucocorticoid has a direct or indirect toxic effect on the pancreatic beta cell (J Kor SOC Endocrinol 18:392-403, 2003).

국내 자동차산업의 개방형 기업간 전자상거래 현황과 확산방안

김유정,정용관,권미수 한국정보사회진흥원 2006 정보화정책 Vol.13 No.3

본 연구의 목적은 최근에 국내 자동차산업에 도입된 B2B 네트워크를 기반으로 한 개방형 기업간 전자상거래의 현황 및 도입 관련 요인을 분석하고, 이를 기반으로 향후 개방형 기업간 전자상거래의 활성화방안을 제시하는데 있다. 이를 위해 본 연구는 158개 자동차업체를 대상으로 설문조사를 실시하였으며, 완성차 업체를 대상으로 심층적인 인터뷰를 수행하였다. 본 연구의 분석결과, 자동차산업에서 개방형 기업간 전자상거래를 위한 B2B 네트워크(KNX, EDI, 부품정보표준, 전자카달로그)의 인지율과 활용율이 낮게 나타난 반면에 B2B 네트워크에 대한 향후 이용의향은 높게 나타났다. B2B네트워크의 도입과 관련된 요인으로 정부의 홍보(정부요인), 거래당사자의 요구 및 상대기업이 사용하지 않음(산업요인), 조직규모, 업무특성, 자동차 업체들의 기존 거래관행 선호, B2B 도입에 따른 전환비용부담, 표준화 된 거래로 인한 전략적 우위 상실(조직요인), B2B 네트워크가 제공하는 상대적 혜택, 기존 기술과의 호환성 부족(기술요인)이 도출되었다. 본 연구 결과를 통해 자동차 산업에 B2B 네트워크의 도입을 촉진할 수 있는 다양한 홍보방안이 수립되고, B2B 네트워크 도입과 관련된 요인에 대한 중점관리 및 실행방안이 우선적으로 수립되어야함을 알 수 있었다. 본 연구에서는 연구결과를 토대로 국내 자동차산업의 개방형 기업간 전자상거래의 활성화를 위한 실행방안을 제시하였다.

임플란트의 collar design이 변연골과 연조직에 미치는 영향

유현상,강선녀,정창모,윤미정,허중보,전영찬 대한치과보철학회 2012 대한치과보철학회지 Vol.50 No.1

연구 목적: 임플란트 경부가 잘 설계된 경우 양호한 연조직 반응을 통해 변연골을 보존하는데 도움이 된다. 본 실험에서는 연, 경조직 경계부에 가장 가까이 위치하는 임플란트의 collar design이 변연골 변화와 연조직 반응에 미치는 영향을 동물실험을 통해 알아보고자 하였다. 연구 재료 및 방법: 2마리의 건강한 Beagle dog에 임플란트 collar design만 다른 두 종류의 임플란트(Neobiotech Co. Seoul, Korea)를 식립하였다. Collar에 bevel 을 부여한 군(Bevel 군)과 "S"자 형태를 부여한 군(Bioseal 군)으로 나누어 마리 당 7개, 군당 7개, 총 14개의 임플란트를 무작위로 식립한 후 Healing abutment를 즉시 체결하였다. 디지털 표준구내 방사선사진을 이용해 4주 간격으로 총 12주간 근원심 변연골 변화를 관찰하였고, 12주에 희생하여 조직학적 분석을 통해 협설 변연골 흡수 및 임플란트 주변 연조직 반응을 평가하였다. Mann-Whitney test를 통해 동일한 방사선 사진 촬영 시점에서 근원심 변연골 변화량 및 조직계측치를 군 간 비교하였고, Kruskal-Wallis test를 통해 방사선 사진상 근원심 변연골 변화량이 시간에 따른 차이가 있는지 군 내 분석 한 후 Duncan test를 통해 사후 검증하였다(α=.05). 결과: 방사선학적 분석 결과 각 촬영 시점에서 두 군간 근원심 변연골 변화량의 차이를 보이지 않았다(P>.05). 군 내에서 시간에 따른 근원심 변연골의 흡수량을 분석한 결과 Bevel 군에서는 시간에 따른 차이를 보이지 않았으나 (P>.05), Bioseal 군에서는 시간에 따른 차이를 보였으며, 4주및8주와 비교했을 때 12주에서 변연골의 증가를 보였다(P<.05). 조직학적 분석 결과 협설측 변연골 흡수량에서 두 군간 차이를 보이지 않았으나 (P>.05), Bevel 군에 비해 Bioseal 군에서 더 견고한 결합조직부착을 관찰할 수 있었으며, 생물학적 폭경의 값은 두 집단 간 차이를 보이지 않은 반면에 (P>.05), 접합상피부착은 Bevel 군에서 유의하게 길었고, 결합조직부착은 Bioseal 군에서 더 길게 나타났다(P<.05). 결론: Bevel 군에 비해 Bioseal 군에서 결합조직부착은 길게 형성된 반면에 접합상피부착은 더 짧게 나타났으며, 생물학적 폭경과 초기 변연골 흡수에는 차이가 없음을 알 수 있었다. 연조직 반응의 차이가 실제 기능하중 하에서 변연골 변화에 미치는 영향에 대해서 향후 연구가 필요할 것으로 생각된다. PURPOSE. The purpose of this study was to investigate the effects of implant collar design on marginal bone change and soft tissue response by an animal test. MATERIALS AND METHODS. Two types of Implant (Neobiotech Co. Seoul, Korea) that only differs in collar design were planted on two healthy Beagle dogs. The implants were divided into two groups, the first group with a beveled collar (Bevel Group) and the second group with "S" shaped collar (Bioseal group). Standardized intraoral radiographs were used to investigate the mesio-distal change of the marginal bone. Histological analysis was done to evaluate the bucco-lingual marginal bone resorption and the soft tissue response adjacent to the implant. Mann-Whitney test was done to compare the mesio-distal marginal bone change at equivalent time for taking the radiographs and the tissue measurements between the groups. RESULTS. Radiographic and histological analysis showed that there was no difference in marginal bone change between the two groups (P>.05). Histological analysis showed Bioseal group had more rigid connective tissue attachment than the Bevel group. There was no difference in biological width (P>.05). Bevel group showed significantly longer junctional epithelium attachment and Bioseal group showed longer connective tissue attachment (P<.05). CONCLUSION. For three months there were no differences in marginal bone change between the Bevel group and the Bioseal group. As for the soft tissue adjacent to the implant, Bioseal group showed longer connective tissue attachment while showing shorter junctional epithelium attachment. There were no differences in biologic width.

수도권 일부 프랑스 레스토랑의 운영 실태 조사

고유정,이희정,주나미 숙명여자대학교 건강·생활과학연구소 2009 生活科學硏究誌 Vol.- No.26

This study is to find the revitalizing method from a survey of overall operation and characteristics of French restaurant in Seoul and Kyeonggido. Sixty-men and women of 20s took part from appointed 60 restaurants in Seoul and Kyeonggido. The statistical analysis conducts by SPSSWIN 12.0 program and the significance level is p<.05, p<.Ol, p<.OO1. The result of operation status of French restaurant is as below. Form of start-up company is popular and the period ofoperation is within 2-5 years. Mostly, restaurant is operated personally. Most of restaurants are located in residential street and apartment complex. 50-100 are most popular in weekdays and weekend customers are more than 100 people in average. So it shows meaningful differences. Most of restaurants carry on business more than 30 days without holidays and open at noon and evening in a day. Monthly rent is popular for form of possession and owners give a weight of passion and interest for applicant when hiring employees and regard management expenses as most important labor cost. Many restaurant get food staff from appointed supplier by competition. Purchase ratio of food staff compared with sales is 25%-30% mostly. 41.7% of people said the future prospect of restaurant is just ''Normal''. Most important thing of menu composition is structure and composition, particularly representative menu and gustatory quality respectively. The important thing is "Taste", sanitation, facilities, menu development, education of employee, price and etc respectively for operation of French restaurant. Sales promotions to attract more customers and relationship with around store are analyzed as less important things. The biggest difficulty is the speedy rising of prime cost for operation of frenches and restaurant, manpower shortage, decreasing customer in this sequence. The difficult for increase offoreign food service and customer complain, decrease of customers is not a big problem in operation of restaurant. This study shows differences from other studies by grasping characteristics of restaurant unlike consideration of simple French dishes and also it is incalculable value to know the overall particulars, importance and difficulties by detailed survey.

放射線이 생쥐生殖細胞에 미치는 影響에 關한 硏究

千基貞,柳炳善,鄭圭會,鄭海元,李鉦浩 대한방사선 방어학회 1985 방사선방어학회지 Vol.10 No.1

The objectives of present study is to investigate genetic damage of radiation in mammalian male germ cell and to establish available screening method for determining genetic hazard by radiation. Several methods were employed to measure the genetic damage of radiation as follows: Sperm head counts, frequency occurrence of sperm with abnormal head shape, fertility, activity of LDH-X, and the induction of unscheduled DNA synthesis (U.D.S.) in male mouse were performed with the passing of time after irradiation by making use of the sequence of event that occurs during spermatogenesis. Sperm head counts and activity of LDH-X in testes were gradually reduced by increased radiation dose and with the passing of the time after irradiation. Frequency occurrence of sperm with abnormal head shape, sterile period, and the induction of unscheduled DNA synthesis were increased by increased radiation dose. It is suggested that since germ cell is a direct reflection of genetic complement, the use of male germ cell is rapid and convenient method for measuring genetic damage by radiation.

비만 개선 효과를 지닌 탄수화물 및 지방 흡수 억제 기능성 식이조성물 개발

윤유식,최선미,홍순복,홍정미,김정원,이홍석,홍성길 한국조리과학회 2002 한국식품조리과학회지 Vol.18 No.3

In a previous study, we developed a new food additive as an egg yolk antibody (IgY) against carbohydrate digestion enzymes for the regulation of blood glucose level and weight control. The IgY delayed and decreased the increment of blood glucose level after administration of sucrose in human being by 30% in 20∼30 min. We also developed a lipase inhibitor as a water extract of two kinds of herb, Platycodon grandiflorum and Solanum melongena. Twenty three volunteers were subjected to the intake of the egg yolk IgY plus the herbal extracts for 50 days. In average, the treated subjects appeared to lose 1.96 ㎏ of body weight and 3.4 ㎏ of body fat mass during the treated period. Furthermore, Panniculus adiposus and breech size were significantly decreased during the experimental period. Above results suggested that the administration of the dietary additives composed of egg yolk IgY and natural herbal extract improve the obesity by the decrement of body weight and body fat mass.

실천적 추론 가정과 수업이 중학생의 도덕성에 미치는 효과

채정현,유태명,박미정,이지연 대한가정학회 2003 Human Ecology Research(HER) Vol.41 No.12

The purpose of thii study was to develop lesson plans and teaching materials applying practical reasoning instruction for the 7th home economics cuniculum content, and to test the effects of practical reasoning instruction on morality of middle school students. This study is a quasiaperimental research with a pretest-postkt &qn. Practical reasoning instruction for experimental group and traditionally lecture oriented insbuction for comparison group were input, and tested the statistical differences between two groups before and after the treatment. The subjects for this study were 8th grade students of a mi& school located in Kwangiu city. Two classes of 76 students homogeneous in characteristics and academic record for each experimental and comparison group were assigned. lnstnunent used for this study was a revised moral indicator, that was developed by KEDI(2001). Spss/wi for 10.0 statistics program was used for analysis of data. ANCOVA was done for testing statistical difference been pretest and posttest of experiment group and comparison group. Result of study which showed statistically significant difference between groups were: 1. V i e of responsibility for words and deeds (from 3.22 to 3.61 for experimental group and from 3.27 to 3.26 for comparison group) in domain of responsibility and cooperation, and virtue of punduality (from 3.59 to 3.76 for experimental group and from 3.41 to 3.28 for comparison group) in domain of trustworthiness, 2. V i e of conversation etiquette (from 3.47 to 3.67 for experimental group and from 3.28 to 3.31 for comparison group) in domain of caring for others, 3. Virtue of forgiveness other s mistakes (from 3.32 to 3.65 for experimental group and from 3.33 to 3.25 for comparison group) in domain of kindness, concession, forgiveness, and virtue of volunteering activity from 2.89 to 3.71 for experimental group and from 3.36 to 3.45 for comparison group) in domain of compassion and service, 4. Virtue of equip the convenient facility for handicapped (from 4.19 to 4.29 for experimental group and from 4.17 to 3.91 for comparison group) in domain of equality and human rights, virtue of recovering selfness for own community (from 2.34 to 2.79 for experimental group and from 2.14 to 2.29 for comparison group), virtue of opposing way of accomplishing purpose by all means (from 3.27 to 3.31 for experimental group and from 3.47 to 3.05 for comparison group), virtue of opposing election of considering aquaintance (from 3.35 to 3.56 for experimental group and from 3.12 to 3.14 for comparison group) in domain of fairness, and virtue of eradication of military force or violence among countries (from 3.49 to 3.57 for experimental group and from 3.38 to 3.05 for comparison group) in domain of love for humanity. The morality of experimental group was improved more than that of comparison group in all of above items. From the results of thii study, following conclusion was drawn. Practical reasoning insbudion in home economics is effective in raising students virtue and value of responsibility in words and deeds, trustworthiness in punctuality, courtesy of not intempting conversation, forgiveness of other s mistakes, volunteering activity, equity for handicapped, fairness opposing selfness for own community, fairness opposing way of accomplishing purpose by all means, fairness opposing election of considering acquaintance, and love for humanity opposing war.

9-12%Cr강의 첨가원소 및 열처리에 따른 미세조직거동과 경도변화

주성욱,유정훈,신기삼,허성강,이재현,석진익,김병훈,김정태 국립7개대학공동논문집간행위원회 2004 공업기술연구 Vol.4 No.-

9-12%Cr steel are getting increasing attention for expanded application as high temperature materials applicable for gas turbine compressors, steam turbine rotors, blade and casing. For efficient and extensive application of 9-12%Cr steel, the data in addition to the improvement of mechanical properties on the correlation of microstructural evolution and mechanical properties are inevitable and thus the investigation in this study is performed for the determination for the specimens heat-treated at 600, 650 and 700℃ for 1000, 3000 and 5000hrs. The microstructure of as-received specimen was tempered martensite, with a high dislocation density and secondary phases. Upon high temperature heat-treatment, the martensite lath got larger and dislocation density decreased resulting the reduction of the strength. In addition, sharp growth of secondary phases was observed in the specimen heat-treated at 700℃ for 5000hrs. A specimen aged at 600℃ and 650℃ Laves phase was observed. The hardness showed close relationship with the secondary phase particle and dislocation density.