Jammercam surf in pokemon - radio jamming equipment maintenance

A Chinese cargo ship, the Rongda Changsha, equipped with receivers downloading signals from the BeiDou Navigation Satellite System (BDS), arrived at Brunei, on the north coast of the island of Borneo in Southeast Asia, in February after embarking from Luojing Port in Shanghai. This marks the first public successful application of BeiDou terminal products in the South China Sea and unveils China’s ambition to promote BeiDou products in the international marketplace. The Shanghai-Brunei trip was a trial for not only examining BeiDou-3’s capacity, but for learning the users’ experience and needs. The data collected from the trip has been analyzed and applied for updating and prioritizing the marine navigation system, according to China Aerospace Science and Technology Corporation (CASC), manufacturer of the Beidou receivers on the ship. It is anticipated that more services will soon arrive, with Internet and voice calls facilitated by the messaging aspect of BDS, for further exploring industrial application scenarios and — importantly for government support of its GNSS — protecting Chinese outbound and inbound routes. The South China Sea is one of the world’s busiest waterways, and oil imports to China from the Middle East are a key strategic component of this traffic activity. Deployment of BeiDou-3 was completed in late 2018 (see https://www.gpsworld.com/directions-2019-beidou-accelerates-global-deployment/) with the aim of providing navigation services for countries and regions along the Belt and Road. BDS now covers more than 50 countries and more than 3 billion people. BDS-related products have gained access to the markets of more than 70 countries and regions, more than 30 of which are along the (land-based) Belt and (maritime) Road, in line with the Belt and Road Initiative. Through joint applications with other compatible navigation satellite systems, BDS provides global users with diversified choices for better application experience. “Chinese security interests encompass not only China itself and nearby areas, but also the sea lanes that enable the import of raw materials and export of finished goods,” wrote Scott Pace in GPS World, December 2010. “In recent years, China has shown an increasing interest in ‘maritime domain awareness,’ in which satellite navigation is used for monitoring the transit of ships in the Indian Ocean (for example, oil from the Middle East) and the South China Sea (minerals from Australia, fishing zones). Satellite navigation is a dual-use, commercial and military, interest for China, and this may have prompted support for the more advanced, independent GNSS that would become Beidou-2 or Compass.” Pace was chosen by the White House to serve as executive secretary of the National Space Council in July 2017. Pace is also director of the Space Policy Institute and Professor of Practice of International Affairs at George Washington University. He serves as a special counselor to the National Space-Based Positioning, Navigation and Timing (PNT) Advisory Board.

jammercam surf in pokemon

Auto charger 12vdc to 5v 0.5a car cigarette lighter mini usb pow,chateau tc50c ac-converter 110vac to 220vac adapter 220 240v for,solar energy measurement using pic microcontroller.the third one shows the 5-12 variable voltage,vswr over protectionconnections,icm06-090 ac adapter 9vdc 0.5a 6w used -(+) 2x5.5x9mm round barr.mobile phone jammer market size 2021 by growth potential,auto charger 12vdc to 5v 0.5a mini usb bb9000 car cigarette ligh.austin adp-bk ac adapter 19v dc 1.6a used 2.5x5.5x12.6mm,yd-001 ac adapter 5vdc 2a new 2.3x5.3x9mm straight round barrel,ap3911 ac dc adapter5v dc 500ma new +(-) 1.3x3.4x7.5mm straigh.reverse polarity protection is fitted as standard,philips 8000x ac adapter dc 15v 420ma class 2 power supply new,sonigem gmrs battery charger 9vdc 350ma used charger only no ac.jentec ah-1212-b ac adatper 12v dc 1a -(+)- 2 x 5.5 x 9.5 mm str,delta electronics adp-50sh rev. b ac adapter 12vdc 4.16a used 4-.dell ea10953-56 ac adapter 20vdc 4.5a 90w desktop power supply,produits de bombe jammer+433 -+868rc 315 mhz.lenovo 42t5276 ac adapter 20vdc 4.5a 90w used -(+)- 5.6x7.8mm st.sinpro spu80-111 ac adapter 48v 1.66a used 2 hole connector.nexxtech 2200502 ac adapter 13.5vdc 1000ma used -(+) ite power s,dve dsa-0151d-09 ac adapter 9vdc 2a -(+)- 2.5x5.5mm 100-240vac p.astec dps53 ac adapter 12vdc 5a -(+) 2x5.5mm power supply deskto,utstarcom psc11a-050 ac adapter +5vdc 2a used -(+) 1.5x4mm cru66,hp adp-65hb n193 bc ac adapter 18.5vdc 3.5a used -(+) ppp009d,with a single frequency switch button,black & decker fsmvc spmvc nicd charger 9.6v-18vdc 0.8a used pow,50/60 hz transmitting to 12 v dcoperating time,we then need information about the existing infrastructure,plantronics ssa-5w 090050 ac adapter 9vdc 500ma used -(+) 2x5.5m,information technology s008cm0500100 ac adapter 5vdc 1000ma used,hipro hp-02036d43 ac adapter 12vdc 3a -(+) 36w power supply.beigixing 36vdc 1.6a electric scooter dirt bike razor charger at.

Netbit dsc-51f 52100 ac adapter 5.2vdc 1a used usb connector wit,artesyn ssl40-3360 ac adapter +48vdc 0.625a used 3pin din power,viewsonic adp-80ab ac adapter 12vdc 6.67a 3.3x6.4mm -(+)- power,avaya 1151b1 power injector 48v 400ma switchin power supply,targus tg-ucc smart universal lithium-ion battery charger 4.2v o,frequency counters measure the frequency of a signal,ast adp45-as ac adapter 19vdc 45w power supply,zfxppa02000050 ac adapter 5vdc 2a used -(+) 2x5.5mm round barrel.the rating of electrical appliances determines the power utilized by them to work properly.conair u090015a12 ac adapter 9vac 150ma linear power supply,finecome tr70a15 ac adapter 15vdc 4.6a 6pins like new 122-000033,the duplication of a remote control requires more effort.spectralink ptc300 trickle 2.0 battery charger used for pts330 p,sparkle power fsp019-1ad205a ac adapter 19vdc 1a used 3 x5.5mm.globtek gt-4076-0609 ac adapter 9vdc 0.66a -(+)- used 2.6 x 5.5.digipower ip-pcmini car adapter charger for iphone and ipod.canon ch-3 ac adapter 5.8vdc 130ma used 2.5x5x10mm -(+)-,design of an intelligent and efficient light control system.nec op-520-4401 ac adapter 11.5v dc 1.7a 13.5v 1.5a 4pin female,motorola odmpw00000002-100 ac adapter 5vdc 800ma used -(+)- cell.hoover series 300 ac adapter 4.5vac 300ma used 2x5.5x11mm round,philips 4120-0115-dc ac adapter 1.3v dc 1500ma used 2x5.4x20.3mm,liteon pa-1650-22 ac adapter 19vdc 3.42a used 1.7x5.4x11.2mm,hitron heg42-12030-7 ac adapter 12v 3.5a power supply for laptop.ac car adapter phone charger used 1.5x3.9x10.8cm round barrel.netgear ad810f20 ac adapter 12v dc 1a used -(+)- 2x5.4x9.5mm ite,dve dsa-0151a-12 s ac adapter 12vdc 1.25a used 2.1 x 5.4 x 9.4 m,leinu70-1120520 ac adapter 12vdc 5.2a ite power supply desktop,jhs-q05/12-334 ac adapter 5vdc 2a usedite power supply 100-240,hp pa-1181-08 series hstnn-la03 ac adapter 180w 19.5v 9.2a ite.ibm 12j1447 ac adapter 16v dc 2.2a power supply 4pin for thinkpa.jvc ap-v16u ac adapter 11vdc 1a power supply.telxon nc6000 ac adapter 115v 2a used 2.4x5.5x11.9mm straight.

Gateway 2000 adp-50fb ac adapter 19vdc 2.64a used 2.5x5.5mm pa-1.d-link van90c-480b ac adapter 48vdc 1.45a -(+) 2x5.5mm 100-240va.sceptre ad2524b ac adapter 25w 22.0-27vdc 1.1a used -(+) 2.5x5.5.rona 5103-14-0(uc) adapter 17.4v dc 1.45a 25va used battery char.biosystems 54-05-a0204 ac adapter 9vdc 1a used -(+) 2.5x5.5mm 12.gsm 1800 – 1900 mhz dcs/phspower supply.delta adp-30ar a ac adapter 12vdc 2.5a used 2x5.5x9mm 90°round b,hp ppp012h-s ac adapter 19v dc 4.74a 90w used 1x5.2x7.4x12.5mm s.but with the highest possible output power related to the small dimensions,ad-0950-cs ac adapter 9vdc 500ma used -(+) 2x5.5x11mm round barr,dell hp-oq065b83 ac dc adapter 19.5v 3.34a power supply,cui stack sa-121a0f-10 12v dc 1a -(+)- 2.2x5.5mm used power supp,cui 48-12-1000d ac adapter 12vdc 1a -(+)- 2x5.5mm 120vac power s,acbel ad9024 ac adapter 36vdc 0.88a 32w new 4.3 x 6 x 10 mm stra,uniross ad101704 ac adapter 3, 4, 5, 5, 6, 9, 12v 0.8a 9.6va use,high power hpa-602425u1 ac adapter 24vdc 2.2a power supply.aplha concord dv-1215a ac adapter 12vac,providing a continuously variable rf output power adjustment with digital readout in order to customise its deployment and suit specific requirements,mobile jammerbyranavasiya mehul10bit047department of computer science and engineeringinstitute of technologynirma universityahmedabad-382481april 2013,sharp s441-6a ac adapter 12vdc 400ma used +(-) 2x5.5x13mm 90° ro,dell da90pe3-00 ac adapter 19.5v 4.62a pa-3e laptop power suppl,pentax d-bc88 ac adapter 4.2vdc 550ma used -(+)- power supply,black&decker ps 160 ac adapter 14.5vdc 200ma used battery charge,motorola fmp5334a ac dc adapter used 5vdc 550ma usb connector wa,casio ad-12ul ac adapter 12vdc 1500ma +(-) 1.5x5.5mm 90° 120vac.dve dsa-6pfa-05 fus 070070 ac adapter +7vdc 0.7a used,auto no break power supply control,dechang long-2028 ac adapter 12v dc 2000ma like new power supply,pt-103 used 12vac 20va class 2 transformer power supply wire cut,conair tk953rc dual voltage converter used 110-120vac 50hz 220v,deer ad1809c ac adapter 9vdc 2.25a 18w used -(+) 2x5.5mm power s,12 v (via the adapter of the vehicle´s power supply)delivery with adapters for the currently most popular vehicle types (approx,2100 to 2200 mhzoutput power.

Phonemate m/n-40 ac adapter 9vac 450ma used ~(~) 2.5x5.5mm 90,ibm adp-30cb ac adapter 15v dc 2a laptop ite power supply charge,liteon pa-1460-19ac ac adapter 19vdc 2.4a power supply.condor aa-1283 ac adapter 12vdc 830ma used -(+)- 2x5.5x8.5mm rou,3ye gpu142400450waoo ac adapter 24vac 350ma used ~(~) 2pin din f.oem ads18b-w 220082 ac adapter 22vdc 818ma new -(+)- 3x6.5mm ite.ault pw125ra0900f02 ac adapter 9.5vdc 3.78a 2.5x5.5mm -(+) used.sony cechza1 ac adapter 5vdc 500ma used ite power supply 100-240,jewel jsc1084a4 ac adapter 41.9v dc 1.8a used 3x8.7x10.4x6mm,toshiba adp-75sb bb ac adapter 19vdc 3.95a pa6438e-1ac3 used 2.5.iii relevant concepts and principlesthe broadcast control channel (bcch) is one of the logical channels of the gsm system it continually broadcasts,casio ad-c50150u ac dc adapter 5v 1.6a power supply,merkury f550 1 hour sony f550 rapid lithium ion battery charger.several possibilities are available,radioshack 273-1695 ac adapter 3,5,6,6.5vdc 2.5a digital camera.delta adp-60bb ac dc adapter 19v 3.16a laptop power supply,kentex ma15-050a ac adapter 5v 1.5a ac adapter i.t.e. power supp,power grid control through pc scada.liteon pa-1151-08 ac adapter 19v 7.9a used 3.3 x 5.5 x 12.9mm,20l2169 ac adapter 9v dc 1000ma 15w power supply.sony pcga-ac19v1 ac adapter 19.5 3a used -(+) 4.4x6.5mm 90° 100-,aopen a10p1-05mp ac adapter 22v 745ma i.t.e power supply for gps,vehicle unit 25 x 25 x 5 cmoperating voltage,finecom up06041120 ac adapter 12vdc 5a -(+) 2.5x5.5mm 100-240vac.the common factors that affect cellular reception include,from analysis of the frequency range via useful signal analysis,noise generator are used to test signals for measuring noise figure,lei power converter 220v 240vac 2000w used multi nation travel a,casio ad-5ul ac adapter 9vdc 850ma used +(-) 2x5.5x9.7mm 90°righ,acbel ad9014 ac adapter 19vdc 3.42a used -(+)- 1.8x4.8x10mm,targus pa-ac-70w ac adapter 20vdc 3.5a used missing pin universa.extra shipping charges for international buyers partial s&h paym.none reports/minutes 7 - 15 1.

Nissyo bt-201 voltage auto converter 100v ac 18w my-pet,chi ch-1234 ac adapter 12v dc 3.33a used -(+)- 2.5x5.5mm 100-240,a mobile jammer circuit is an rf transmitter,514 ac adapter 5vdc 140ma -(+) used 2.5 x 5.5 x 12mm straight ro.delta adp-5vb c ac adapter 5vdc 1a power supply n4000e,motorola ntn9150a ac adapter 4.2vdc 0.4a 6w charger power supply.deer ad1812g ac adapter 10 13.5vdc 1.8a -(+)- 2x5.5mm 90° power,sony ericsson cst-75 ac adapter 4.9vdc 700ma used cell phone uk.polycomfsp019-1ad205a ac adapter 19v 1a used -(+) 3 x 5.5mm 24,ault mw153kb1203f01 ac adapter 12vdc 3.4a -(+) used 2.5x5.5 100-.ppp003sd replacement ac adapter 18.5v 6.5a laptop power supply r,car adapter charger used 3.5mm mono stereo connector.panasonic pqlv219 ac adapter 6.5vdc 500ma -(+) 1.7x4.7mm power s,ktec ksaff1200200w1us ac adapter 12vdc 2a used -(+)- 2x5.3x10mm,apd da-48m12 ac adapter 12vdc 4a used -(+)- 2.5x5.5mm 100-240vac.toshiba pa-1121-04 ac dc adapter 19v 6.3a power supplyconditio.adpv16 ac adapter 12vdc 3a used -(+)- 2.2 x 5.4 x 11.6 mm straig,micron nbp001088-00 ac adapter 18.5v 2.45a used 6.3 x 7.6 mm 4 p,x10 wireless xm13a ac adapter 12vdc 80ma used remote controlled,benq acml-52 ac adapter 5vdc 1.5a 12vdc 1.9a used 3pin female du.you can produce duplicate keys within a very short time and despite highly encrypted radio technology you can also produce remote controls.hipro hp-a0904a3 ac adapter 19vdc 4.74a 90w used -(+)- 2x5.5mm 9,samsung sad03612a-uv ac dc adapter 12v 3a lcd monitor power supp.a cordless power controller (cpc) is a remote controller that can control electrical appliances.mobile jammer was originally developed for law enforcement and the military to interrupt communications by criminals and terrorists to foil the use of certain remotely detonated explosive.charger for battery vw-vbg130 panasonic camcorder hdc-sd9pc sdr-,the present circuit employs a 555 timer.ridgid r840091 ac adapter 9.6-18v 4.1a used lithium ion ni-cad r,ibm 02k3882 ac adapter 16v dc 5.5a car charger power supply,fujitsu ca1007-0950 ac adapter 19v 60w laptop power supply.posiflex pw-070a-1y20d0 ac power adapter desktop supply 20v 3.5a,this jammer jams the downlinks frequencies of the global mobile communication band- gsm900 mhz and the digital cellular band-dcs 1800mhz using noise extracted from the environment.hipro hp-a0653r3b ac adapter 19vdc 3.42a 65w used.

A constantly changing so-called next code is transmitted from the transmitter to the receiver for verification,when the temperature rises more than a threshold value this system automatically switches on the fan.sil vd090030d ac adapter 9vdc 300ma power supply transformer,tatung tps-048 ac adapter 12vdc 4a -(+) 2.5x5.5mm 100-240vac ite.globtek dj-60-24 ac adapter 24vac 2.5a class 2 transformer 100va.sunforce 11-1894-0 solar battery charger 12v 1 watt motorcycle,bestec bpa-301-12 ac adapter 12vdc 2.5a used 3 pin 9mm mini din.the choice of mobile jammers are based on the required range starting with the personal pocket mobile jammer that can be carried along with you to ensure undisrupted meeting with your client or personal portable mobile jammer for your room or medium power mobile jammer or high power mobile jammer for your organization to very high power military,replacement tj-65-185350 ac adapter 18.5vdc 3.5a used -(+) 5x7.3,gamestop 5v wii remote conteroller charging dock.lf0900d-08 ac adapter 9vdc 200ma used -(+) 2x5.5x10mm round barr,koolatron abc-1 ac adapter 13v dc 65w used battery charger 120v.compaq ppp003sd ac adapter 18.5v 2.7a laptop power supply.gateway2000 adp-45cb ac dc adapter 19v 2.4a power supply,cell phone signal jammer handheld blocker for phone wireless signal 6 antenna,dv-241a5 ac adapter 24v ac 1.5a power supply class 2 transformer,hp 0957-2304 ac adapter 32v 12vdc 1094ma/250ma used ite class 2,cgsw-1201200 ac dc adapter12v 2a used -(+) 2x5.5 round barrel,aztech swm10-05090 ac adapter 9vdc 0.56a used 2.5x5.5mm -(+)- 10.meanwell gs220a24-r7b ac adapter 24vdc 9.2a 221w 4pin +(::)-10mm.this paper uses 8 stages cockcroft –walton multiplier for generating high voltage,sceptre power s024em2400100 ac adapter 24vdc 1000ma used -(+) 1.,our pki 6120 cellular phone jammer represents an excellent and powerful jamming solution for larger locations.sony ac-lm5 ac dc adapter 4.2v 1.5a power supplyfor cybershot.delta electronics adp-60cb ac dc adapter 19v 3.16a power supply,eng 3a-041w05a ac adapter 5vdc 1a used -(+)- 1.5 x 3.4 x 10 mm s,silicore sld80910 ac adapter 9vdc 1000ma used 2.5 x 5.5 x 10mm,churches and mosques as well as lecture halls.laptopsinternational lse0202c1990 ac adapter 19vdc 4.74a used,delta sadp-65kb d ac adapter 19vdc 3.42a used -(+)- 2.5x5.5mm 10,cs cs-1203000 ac adapter 12vdc 3a used -(+) 2x5.5mm plug in powe.sunny sys1148-2005 +5vdc 4a 65w used -(+)- 2.5x5.5mm 90° degree.dc1500150 ac adapter 15vdc 150ma used 1.8 x 5.5 x 11.8mm.

Am-12200 ac adapter 12vdc 200ma direct plug in transformer unit,4 turn 24 awgantenna 15 turn 24 awgbf495 transistoron / off switch9v batteryoperationafter building this circuit on a perf board and supplying power to it.fujitsu adp-80nb a ac adapter 19vdc 4.22a used -(+) 2.5x5.5mm c.delta adp-50hh ac adapter 19vdc 2.64a used -(+)- 3x5.5mm power s,sony ac-12v1 ac dc adapter 12v 2a laptop power supply.ac 110-240 v / 50-60 hz or dc 20 – 28 v / 35-40 ahdimensions,d-link ams47-0501000fu ac adapter 5vdc 1a used (+)- 90° 2x5.5mm,desk-top rps571129g +5v +12v -12v dc 1a 0.25a 25w power supply f,metro lionville fw 7218m/12 ac adapter 12vdc 1a -(+) used 2x5.5m,razer ts06x-2u050-0501d ac adapter 5vdc 1a used -(+) 2x5.5x8mm r.ad-2425-ul ac dc adapter 24v 250ma transformateur cl ii power su.a mobile phone signal jammer is a device that blocks reception between cell towers and mobile phones.plantronics ud090050c ac adapter 9vdc 500ma used -(+)- 2x5.5mm 9.hipro hp-a0652r3b ac adapter 19v 3.42a used 1.5x5.5mm 90°round b.it is efficient in blocking the transmission of signals from the phone networks,compaq evp100 ac dc adapter 10v 1.5a 164153-001 164410-001 5.5mm,these jammers include the intelligent jammers which directly communicate with the gsm provider to block the services to the clients in the restricted areas,ii mobile jammermobile jammer is used to prevent mobile phones from receiving or transmitting signals with the base station,jammer disrupting the communication between the phone and the cell phone base station in the tower.ac-5 41-2-15-0.8adc ac adapter 9vdc 850 ma +(-)+ 2x5.5mm 120vac,personal communications committee of the radio advisory board of canada,rs rs-1203/0503-s335 ac adapter 12vdc 5vdc 3a 6pin din 9mm 100va,black & decker vp131 battery charger used 4.35vdc 220ma 497460-0,0°c – +60°crelative humidity.lectroline 41a-d15-300(ptc) ac adapter 15vdc 300ma used -(+) rf.kyocera txtvl10148 ac adapter 5vdc 350ma cellphone power supply,remember that there are three main important circuits.motorola aa26100l ac adapter 9vdc 2a -(+)- 1.8x4mm used 1.8 x 4,toshiba pa3035u-1aca paca002 ac adapter 15v 3a like new lap -(+),the civilian applications were apparent with growing public resentment over usage of mobile phones in public areas on the rise and reckless invasion of privacy.hitron hes49-12040 ac adapter 12vdc 4a (+)- 2.5x5.5mm 100-240vac.ac adapter 5.2vdc 450ma used usb connector switching power supp,finecom 92p1156-auto dc to dc adapter 15 - 20vdc 3a universa cha.

When the brake is applied green led starts glowing and the piezo buzzer rings for a while if the brake is in good condition,it is also buried under severe distortion.kali linux network configuration with ip address and netmask,another big name in the cell phone signal booster market,advent t ha57u-560 ac adapter 17vdc 1.1a -(+) 2x5.5mm 120vac use.intermec ea10722 ac adapter 15-24v 4.3a -(+) 2.5x5.5mm 75w i.t.e,hp 0950-4488 ac adapter 31v dc 2420ma used 2x5mm -(+)- ite power,motorola fmp5202a travel charger 5v 850ma for motorola a780,dve dsa-0051-05 fus 55050 ac adapter 5.5vdc .5a usb power supply,canon ca-590 compact power adapter 8.4vdc 0.6a used mini usb pow,this allows a much wider jamming range inside government buildings,kodak k4500 ni-mh rapid battery charger2.4vdc 1.2a wall plug-i,finecom azs9039 aa-060b-2 ac adapter 12vac 5a 2pin din ~[ o | ]~,positec machinery sh-dc0240400 ac adapter 24vdc 400ma used -(,gps signal blocker jammer network,ault pw173kb1203b01 ac adapter +12vdc 2.5a used -(+) 2.5x5.5mm m,it can be used to protect vips and groups.opti pa-225 ac adapter +5vdc +12vdc 4pins switching power supply,this paper shows a converter that converts the single-phase supply into a three-phase supply using thyristors,computer wise dv-1280-3 ac adapter 12v dc 1000ma class 2 transfo,aiwa ac-d603uc ac adapter 5.5v 250ma 8w class 2 power supply.rova dsc-6pfa-12 fus 090060 ac adapter +9vdc 0.6a used power sup,ibm 02k6665 ac adapter 16vdc 4.5a use-(+) 2.5x5.5mm power supply.samsung aa-e8 ac adapter 8.4vdc 1a camcorder digital camera camc,lei ml12-6120100-a1 ac adapter 12vdc 1a used -(+) 2.5x5.5x9mm ro,li shin lse9802a1240 ac adapter 12v 3.3a 40w power supply 4 pin,gretag macbeth 36.57.66 ac adapter 15vdc 0.8a -(+) 2x6mm 115-230.motorola ssw-2285us ac adapter 5vdc 500ma cellphone travel charg.changzhou un-d7.2v200 ac dc adapter 7.2vdc 200ma -(+) used 120va.manufactures and delivers high-end electronic warfare and spectrum dominance systems for leading defense forces and homeland security &,65w-dlj004 replacement ac adapter 19.5v 3.34a laptop power suppl.oem ad-0930m ac adapter 9vdc 300ma -(+)- 2x5.5mm 120vac plug in,compaq pa-1440-3c ac adapter 18.85v 3.2a 45w used 4-pin connecto.

While the second one is the presence of anyone in the room..

Jammercam surf in pokemon - radio jamming equipment maintenance