SEM QUEBRAR AS TA&CAS!! (PDF Download Available)
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18.94Universidade Federal do Rio Grande do SulAbstractResumo Uma ripa de madeira, apoiada sobre duas ta?as, pode ser partida, sem quebrar as ta?as, com uma forte pancada. A demonstra??o deste surpreendente efeito em sala de aula, seguida de sua explica??o, conduz ao aprofundamento teórico de conceitos físicos, em especial daqueles relacionados à din?mica das rota??es. Palavras-chave: Experimento contra-intuitivo, eixo instant?neo de rota??o, din?mica das rota??es.Discover the world's research14+ million members100+ million publications700k+ research projects
64 SEM QUEBRAR AS TA?AS!!*
Fernando Lang da Silveira Instituto de Física – UFRGS Porto Alegre – RS
Uma ripa de madeira, apoiada sobre duas ta?as, pode ser partida, sem quebrar as ta?as, com uma forte pancada. A demonstra??o deste surpreendente efeito em sala de aula, seguida de sua explica??o, conduz ao aprofundamento teórico de conceitos físicos, em especial daqueles relacionados à din?mica das rota??es.
Palavras-chave: Experimento contra-intuitivo, eixo instant?neo de rota??o, din?mica das rota??es. I. Introdu??o ? possível, sem quebrar as ta?as, partir uma ripa de madeira sobre ta?as de vinho? A resposta é positiva e você pode facilmente realizar tal fa?anha. Em primeiro lugar mostraremos como realizá-la e em seguida daremos uma explica??o. II. Realizando a fa?anha Tome uma ripa de madeira de 40 cm ou mais de comprimento. Se ela for de pinho pode ter 1 cm de espessura. Se for de madeira aglomerada pode ser mais grossa. Apóie a ripa pelas extremidades sobre as duas ta?as conforme a Fig. 1 (caso tenha receio de realizar a fa?anha com as ta?as, teste com dois copos de vidro comuns ou descartáveis de plástico). Uma barra de madeira resistente (ou até de metal) com cerca de 1 m de comprimento será utilizada para golpear violentamente a ripa de madeira em sua regi?o mediana. O golpe deve ser muito forte!!
* Publicado no Caderno Catarinense de Ensino de Física, v. 12, n. 2, ago. 1995.
Fig. 1 - Ripa deitada sobre as ta?as. III. A explica??o da fa?anha O golpe violento na ripa produzirá uma for?a muito grande na regi?o mediana da ripa. Se a situa??o fosse estática, teríamos cerca da metade dessa for?a aplicada a cada ta?a, e conseqüentemente, seriam quebradas. Na verdade essa for?a intensa atuará na regi?o mediana da ripa por um breve intervalo de tempo, durante o qual ainda n?o há qualquer esfor?o sobre as ta?as. Aplicada uma for?a na regi?o mediana da ripa, os esfor?os sobre as extremidades acontecer?o depois de algum tempo (o tempo que uma onda mec?nica se propagando na ripa leva para percorrer a dist?ncia que separa o local do impacto das extremidades apoiadas). Ou seja, antes de haver esfor?o sobre as ta?as a ripa já está rompida, constituindo-se ent?o dois corpos independentes. O golpe transferirá para cada peda?o da ripa uma grande quantidade de movimento linear e angular. Ou seja, cada parte da ripa terá em seguida ao golpe o seu centro de massa se deslocando para baixo com grande velocidade, Concomitantemente o peda?o girará com grande velocidade angular em torno do centro de massa (vide a Fig. 2).
Fig. 2 - Transla??o do centro de massa e rota??o em torno do centro de massa de cada peda?o. A superposi??o da transla??o de cada peda?o com a rota??o em torno do centro de massa determinará que ele gire instantaneamente em torno de um eixo (eixo instant?neo de rota??o) situado acerca de um ter?o do eu comprimento da extremidade apoiada na ta?a (vide a Fig. 3). Desta forma, instantaneamente, o movimento é uma rota??o pura em torno do eixo instant?neo e a extremidade apoiada na ta?a está subindo, se afastando da ta?a.
Fig. 3 - Rota??o para cada peda?o em torno do eixo instant?neo. Você também pode realizar este experimento suspendendo a ripa pelas extremidades em duas al?as de papel higiênico. Verá ent?o que as al?as de papel n?o s?o rasgadas. Temos utilizado este experimento em disciplinas de Física Geral. Ele serve para exemplificar concretamente a existência de um eixo instant?neo de rota??o - quando o movimento de um corpo é descrito como uma rota??o em torno de um eixo com transla??o desse mesmo eixo - facilitando dessa forma o entendimento de um conceito muitas vezes incompreensível para os alunos. Concluiremos este trabalho apresentando uma demonstra??o sobre a localiza??o do eixo instant?neo de rota??o. IV. Localizando o eixo instant?neo de rota??o A barra da Fig. 4 representa um dos peda?os da ripa, sob a a??o de uma for?a percussora F aplicada a uma de suas extremidades. Como a for?a percussora F produzida pela pancada é muito maior do que quaisquer outras for?as que estejam aplicadas à barra, podemos considerá-la como a for?a resultante na barra durante o pequeno intervalo de tempo que dura a pancada.
Fig. 4 - For?a sobre um dos peda?os da barra durante a pancada.
F a única for?a que atua sobre a barra, o torque de
F ( Fτ)é o torque resultante ( sReτ) sobre a barra. Ou seja,
Fs τ=τRe
(1) O torque de F em rela??o ao eixo instant?neo de rota??o é:
()2LDFF+=τ
(2) O torque resultante é o produto do momento de inércia da barra em rela??o ao eixo instant?neo (Io) pela acelera??o angular da barra em rela??o ao eixo instant?neo(αo).
oos Iα=τRe
(3) O momento de inércia da barra em rela??o ao eixo instant?neo está relacionado com o momento de inércia da barra em rela??o ao seu centro de massa (ICM) através do teorema de Steiner (teorema dos eixos paralelos). Sendo M a massa da barra, o teorema é dado por:
2CMo DMII +=
(4) Sabe-se que o momento de inércia da barra em rela??o ao centro de massa é:
12LMI2CM =
(5) Substituindo-se (5) em (4) obtém-se:
22oDM12LMI+=
(6) Substituindo-se (6) em (3) encontra-se:
o22sDM12LM α????????+=τRe
(7) Substituindo-se (7) e (2) em (1) chega-se em:
??????+=α????????+2LDFDM12LMo22
(8) A acelera??o angular αo está relacionada com a acelera??o linear do centro de massa (aCM) através de:
(9) A Segunda Lei de Newton permite reescrever (9) como:
(10) Substituindo-se (10) em (8) obtém-se:
??????+=????????+2LDFDMFDM12LM 22
(11) Simplificando-se F e M em (11) encontra-se:
??????+=????????+2LDD1D12L22
(12) A seguir obtém-se:
2DLDD12L222+=+
6LD2D12L==>=
(14) Na Fig. 4 percebe-se que:
(15) Substituindo-se (14) em (15) encontra-se:
(16) Finalmente, como queríamos demonstrar, obtém-se:
ArticleFull-text availableJun 2003ArticleFull-text availableJun 2003ProjectAtualmente o meu projeto é N?O ter projeto. Meu trabalho no CREF - http://www.if.ufrgs.br/cref/?area=indice , respondendo dúvidas, tem nos últimos anos motivado diversas publica??es. ArticleApril 2003Resumo Os mecanismos responsáveis pelas marés s?o discutidos, utilizando-se uma matemática acessível a alunos de ensino mé demonstra-se que tanto a Lua, quanto o Sol s?o responsáveis pelos efeitos de maré nos oceanos. Apesar da for?a gravitacional do Sol na Terra ser aproximadamente 200 vezes maior do que a da Lua, os efeitos solares de maré s?o aproximadamente 2 vezes menores do que os... [Show full abstract]DataDecember 2017Esta é vers?o final do artigo publicado na revista Física na Escola. ArticleMarch 2011 · A model for a motor vehicles' tractive power as a function of the speed, the rolling resistance on their wheels, and the air's aerodynamic drag force, is proposed. Based on both nominal top power and top speed data of 155 vehicles, an empiric test for this model is presented, and corroborates the assumption that the top power is related to the cube of the top speed. ArticleArticleOctober 2011http://dx.doi.org/10.41.p468
Um vídeo educativo do Monash University Accident Research Centre inspira a proposi??o de um problema de cinemática com um resultado contraintuitivo. A solu??o do problema tem como pressupostos conhecimentos sobre a acelera??o máxima possível em frenagens de emergência, bem como do intervalo de tempo que transcorre entre a percep??o do perigo... [Show full abstract]Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.This publication is from a journal that may support self archiving.SEM|利用A/B测试优化推广创意-营口热线
SEM|利用A/B测试优化推广创意
在传统广告界，广告案牍创意是特别重要的一个环节，众多经典的广告案牍，朗朗上口，振聋发聩，被口口传播。SEM也需求创意。许多从业者说推行创意很重要，对关键词质量度、点击率有影响；有的人则认为，创意的点击率，跟关键词出价、排名有很大关系，只需不是特别不靠谱的创意，就OK了，差不多便可，它不是决定因素。正所谓一千个厨子就有一千盘酸辣土豆丝，在此我可是多谈创意的重要性，先说说大家比较感兴致，也特别适用的创意优化技能。我们晓得创意的展现方式有两种，一种是优选，一种是轮番。笔者这边建议应用轮番。假如我们一开始就采取优选的创意展现方式，那么后期的创意优化，根本就是扯淡，新增的创意，基本都没有展现的机遇；而你想要再换成轮番，则面对着各类推行数据的下降，依据我的视察，基本上有10%-20%的下降幅度，亏损很大。固然了，假如你的账户比较大，人手不够，忙可是来，能够轮番一段时间后，换成优选。用优选以后，创意这块的优化，要少花许多时间和精力。关于低预算账、中小型账户，个人建议还是用轮番，不单单只是为了优化创意，再进一步，还能追踪到不一样创意的转化数据。言归正传，下头笔者以百度推行中的“英语培训”这个行业为例子，来讲一下如何利用A/B测试的原理来优化创意。在SEM过程当中，我们推断一个推行创意的好坏，基本上是以该创意的点击率来决定的。我们大部分SEM从业者都晓得，在推行创意里，普通都写入自己公司或产品的优势、价钱、折扣等卖点信息，以期能通太短短的100来个字，吸引访客。目前我们先去百度推行看看，“英语培训”这个行业各个机构的卖点也许有哪些：1、免费试听2、老外教授讲课3、上课时间自在4、培训课程量身定制好了，关于“英语培训”这个行业，我大致总结了4个卖点，那么我们应当如何组合这些卖点来写创意呢？我的一家之言是：我们固然不也许在一个创意里只写一个卖点，我们能够依据产品卖点的多少，来决定一条创意写多少个卖点。比方举例的“英语培训”，我有4个卖点，那么在测试早期，一条创意里包括3个卖点就够多了，那么通过组合，我大致能够写4个创意，他们分别包括不一样的卖点，以下：创意1：免费试听、老外教授讲课、上课时间自在创意2：免费试听、老外教授讲课、培训课程量身定制创意3：免费试听、上课时间自在、培训课程量身定制创意4：老外教授讲课、培训课程量身定制、上课时间自在然后通过创意轮番，在不转变出价的条件下，测试三、五天，通过创意报表，我们能够获得这些创意的点击率，以下。数据由我虚拟，我分享的是思绪。创意1：点击率—3.94%创意2：点击率—5.38%创意3：点击率—2.84%创意4：点击率—3.25%把点击率数据对应到卖点，能够看到不一样卖点的点击率，以下：免费试听：(3.94%+5.38%+2.84%)/3=4.05%老外教授讲课：(3.94%+5.38%+3.25%)/3=4.19%上课时间自在：(3.94%+2.84%+3.25%)/3=3.34%培训课程量身定制：(5.38%+2.84%+3.25%)/3=3.82%趁便提一句，也许有人会说，测试期间他人提升排位或许下降排名怎样办？这个比较少见，特别是成熟的行业，份额都差不多会固定。固然，为了保障数据的精确性，你能够测试更长时间。通过数据，我们大致能够得出这样的信息——卖点“老外教授讲课”最重要、其次是“免费试听”、再次是“培训课程量身定制”。在接下来写创意的过程当中，久能够将最重要的卖点突出，比方写在创意题目中，写在右边推行链接和左边推行位链接的创意中。甚至，经太长时间的测试，久而弥坚，能够在网页上也强化这样的卖点。假如你没有权力和资源调动其他部门的人去做网页的A/B测试，这起码让你能够从你推行的数据跟BOSS提下网站谋划、运营的建议。至此，这个利用A/B测试的原理来优化推行创意的思绪分享就差不多了。A/B测试的原理用处特别普遍，除过推行创意，还有客服话术、产品价钱、网站谋划等。关于百度推行创意优化，假如您有什么其他思绪，记得分享给我。有首诗是这样写的，我认为还不错：远算作岭侧成峰，测试以后知不一样；不问路人哪有酒，他也不知杏花村；只是一片月光光，哪来床前鞋两双；爱过方知肉痛，醉过方知酒浓。——没有试过，就没有答案。
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When it comes to monitoring Exchange, there are multiple choices, involving products that can monitor every aspect of the platform.&However sometimes it is useful to have a quick overview of whether the Exchange services are available, and with the increasing dependence on mobile working, whether they are available from the outside world.&Fortunately, Exchange 2013 and higher provides a built in mechanism that allows you to build a quick and easy overview of Exchange using a free monitoring service.The External ServiceFor the purposes of this article, we are using Uptime Robot
. This provides a five minute check for up to fifty checks, and also provides a publicly available status page. That is useful to distribute to end users to check whether Exchange is available or not.The Exchange MechanismIntroduced with Exchange 2013, each of the core Exchange web based services has a health check page. This can be checked with no authentication required and will confirm if the service is working or not. Primarily designed for use with load balancers, so they can check if the server is available, it is also useful for the purpose of monitoring.&If you browse to the following URL, then you will see what I mean: https://host.example.com/owa/healthcheck.htm (where host.example.com is the host name used by your Exchange server).&You should see something like this:The full list of URLs that can be checked in that way are:Outlook Anywhere (aka RPC over HTTP): /rpc/healthcheck.htmMAPI/HTTP: /mapi/healthcheck.htmOutlook Web App (aka Outlook on the web): /owa/healthcheck.htmExchange Control Panel: /ecp/healthcheck.htmExchange ActiveSync: /Microsoft-Server-ActiveSync/healthcheck.htmExchange Web Services: /ews/healthcheck.htmOffline Address Book: /oab/healthcheck.htmAutoDiscover: /Autodiscover/healthcheck.htmSetting up the ChecksThe type of monitor you want is "Keyword". Enter a friendly name for the monitor - this is what will be seen by anyone browsing to the public status page.&For the URL, use your public URL, in the format above.&For the keyword, use the name of the server as it appear when you browse to the server. In most cases this will be the server name in all upper case. That the name doesn't resolve externally doesn't matter. You need to change it to "Keyword NOT exists".&You can then add an alert contact. An external email address would be a good option here, but there is also an App available.&Repeat for all of the URLs listed above, until you get a list like this:I have added in a check on the SMTP port as well. If you publish IMAP/POP3 then add those ports too.&That is all there is to it. If you stop the IIS services then you will get a screen like this:&Within the Uptime Robot site you can then create a public status site - which uses a CNAME on your domain to point to a site on their server - secured with an SSL certificate by default.&This is a link to a screenshot of the status site for the above checks:This URL can be included in any pre-populated bookmarks that are pushed to users - including on phones using your MDM product, so end users can check whether Exchange is available and whether it has been down earlier.&Furthermore, as it is an externally hosted service it also can give you a quick overview from inside the office if things are working correctly. Just remember to add the same internal CNAME entry if you are using the same domain internally and externally via split DNS.&What if you are behind a load balancer already?In that case, give each server a unique URL (which is good practise anyway) and then configure Uptime Robot to connect to it directly. The IP addresses for the monitors are on their web site:&A similar practise would allow you to monitor Exchange if behind a device in a DMZ.&The SMTP Port Monitor doesn't confirm it is working?&Indeed that is the case - Transport can often stop accepting emails, but will still have the port open. For proper testing of SMTP traffic, you need to use a round trip mail monitor.&&. That will alert you as the administrator directly if mail flow stops for whatever reason. Again use an external email account, rather than one on Exchange.&
Now starting to see more implementations of Windows 2016 and Exchange 2016, so odd issues are starting to come to light. One that I have seen a few times is a problem with Macs connecting to EWS on the 2016 versions of Exchange and Windows. Going through the logs, there are 401 errors (unauthorised), yet the same credentials work with OWA. Further troubleshooting with the web server and a hint on an Apple forum suggested that Windows 2016 was using HTTPS 2 by default and that the Mac was having some problems working with that for authentication. The fix was to downgrade to HTTP 1.1.HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\HTTP\ParametersNew DWORD valuesEnableHttp2CleartextEnableHttp2TlsSet both to a value of 0. The first one is for HTTP, the second for HTTPS. I set both, even though in most cases only HTTPS is allowed to the server and being used. Reboot the server (restarting the IIS services does not appear to work). Here is the registry value content to create a reg file for easy installation:Windows Registry Editor Version 5.00[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\HTTP\Parameters]"EnableHttp2Tls"=dword:"EnableHttp2Cleartext"=dword:From an operational point of view, I cannot see any loss of functionality. OWA is designed to work with Windows 2012 R2 which still uses HTTP 1.1. In very large environments you might see a small performance hit because of the loss of the optimisations provided by HTTP 2, but most systems will not see anything.
Spent most of the
week dealing with a flapping DAG database - flipping between two servers, which
turned out to be a bad network cable.
Anyway, while trying
to get the databases to activate correctly during troubleshooting I hit this
lovely error (real server name/database changed).
Error: Mailbox
Database 1
An Active Manager
operation failed. Error: The database action failed. Error: Move for database
'Mailbox Database 1’ was suppressed because too many moves have happened
recently. 3 moves have happened within 01:00:00. [Database: 'Mailbox Database
1', Server: exch1.example.com]
Basically tried to
activate a database three times in a hour and Exchange stops it from happening
Off to PowerShell
and skip the checks:
Move-ActiveMailboxDatabase
-Identity "Mailbox Database 1" -SkipMoveSuppressionChecks
-ActivateOnServer exch1.example.comFixed
Many years ago I wrote about how I was getting good results with the anti-spam technique greylisting. It is still a technique I use with many clients.&However with the increasing use of cloud based services, I have found that greylisting can delay legitimate traffic, because the email can be delivered from different IP addresses on each attempt.&While Vamsoft does have an option to Accept delivery retries from the same 24 subnet, this is not always effective because the large providers have bigger IP address pools.&Therefore I have started whitelisting the major providers within the Vamsoft product.&Another feature I use with Vamsoft is their Honeypot function - the same lists for greylisting I am using with this feature as well - as a single bad address will cause a lot of senders to get blocked.&Getting the Lists of IP AddressesThe first thing to do is get the IP addresses. I am putting in Office365, Google Apps, Mimecast and Amazon SES. If you have senders on other cloud providers then you should add those addresses as well.&For Office365 and Mimecast, the list of IP addresses is on their web site.&Office365: Mimecast: Google AppsFor Google apps, you need to do an NSLOOKUP to get the current list.&First query their SPF record:nslookup -q=TXT _spf.google.com 8.8.8.8Then query each result, which at the time of writing was this:nslookup -q=TXT _netblocks.google.com 8.8.8.8nslookup -q=TXT _netblocks2.google.com 8.8.8.8nslookup -q=TXT _netblocks3.google.com 8.8.8.8Although at the time of writing, Netbblocks 2 is ipV6, which you may not need.&Amazon SES:&Similar to Google, query their DNS records:nslookup -type=TXT amazonses.com | find "v=spf1"Entering the Lists in to VamsoftOnce you have the lists, you are ready to put them in to Vamsoft. The GUI I find is a little cumbersome for this task, and if you have lots of servers will take a long time. Therefore modify the configuration file instead.&First, check whether you have any IP addresses in the white list - Blacklists --& Greylisting --& IP Exceptions. If you don't, add one, as this will create the relevant part of the configuration file and the format.&Next, option an elevated command prompt and enter this:notepad "c:\Program Files (x86)\ORF Fusion\orfent.ini"Then look for the section&[GreylistingHostExceptions]The following the format, add the IP addresses like this:101=V5"23.103.132.0/22","Office365"The number at the start has to be unique. I usually start at 101 as it will ensure it doesn't conflict with any existing entries - usually creating it in a separate Notepad file and then copying the result in to the configuration file.&Save the configuration file and close it. Finally start the Vamsoft Administration tool and check the list has your addresses in it. If it does, save the file, which will sort out the numbering for you correctly. For the Honeypot feature, repeat above, but instead put the same list of IP addresses in to the section headed[HoneypotIpExceptions]Check the lists regularly - as the providers will add additional IP addresses and you need to update them.&
Over five years ago I wrote about a self-contained environment I built for a small business where& they had no office of their own. A new client recently contacted me and asked if I had done anything similar recently, but using more up to date technologies. With the growth of cloud tech, Office365 etc, things have moved on. This particular request was to provide Exchange for a project which was quite sensitive and the client didn't want to put the data in to Office365, but was quite happy to put it in to a private cloud using a dedicated server. It needed to be completely self-contained. No problem, as that is how I build my labs, so it was just scaled up. This is what I proposed and was deployed at the beginning of September. HardwareDedicated Server rented from a major host here in the UK (I can actually tell you where the server is located). Fairly standard specification, dual RAID 1 arrays, 32gb of RAM. SoftwareInstalled on to the physical server was VMWARE 6.x.VM GuestsInto that VMWARE server I installed the following guestsPfsense. This provided the firewall for the entire environment, and once the builds were complete, the VMWARE admin console was put behind this as well. Windows 2012 R2 DC (8gb RAM) Fairly obvious one - separating the Exchange server and the domain controller. Windows 2012 R2 Exchange 2016 (16GB RAM) This was the main Exchange server. Exchange 2016 Latest version of Exchange, naturally. GFI Mail Essentials Providing malware, spam and attachment filtering, plus automatic signatures. SSL Certificate - from
Observium monitoring appliance from Turnkey Linux (open source) This provides a good overview of the virtual machines. The host was also kind enough to setup a read only user on the IPMI interface of the server. Windows 10 Pro workstation (4gb RAM) This had Office 2016 installed on it, along with some other tools to allow testing of the implementation from the server itself. It also provides a landing point should one of the end users need to access the server and doesn't have the tools available immediately. The Windows servers also got the various monitoring tools I use with my Exchange clients. Backup to the cloud, using Exchange aware backup application was also provided.Microsoft OfficeShortly after deployment, it became apparent that the clients were a complete mixture of Office versions, some of which didn't support the latest version of Exchange. Therefore I proposed, and was accepted, that we used Office365 Business subscription. This provided Microsoft Office for both the Windows machines used by the users, plus their tablets and phones. I integrated the domain I built with their new Office365 subscription providing a single username and password experience - the size of the deployment didn't justify a single sign on implementation. Should someone leave the project, we simply un-licence their Office installation. Costs?All numbers correct at the time of writing (September 2016) and are excluding VAT. Hosted Server: ?140 a month Per user licences: ?25 a month (covers Exchange, Windows Server etc)Office365: ?7 a month per userServer management Fee: ?350/monthSetup: ?1500 (includes hosting company setup charge and my time).&SSL Certificate: ?35/year. ConclusionThe client has a solution that they can scale up and down as the project progresses, which fulfils their requirements of being a self-contained standalone solution, without the cost of the hardware and software up front. It is also managed for them by Sembee Ltd with responsive monitoring.
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