Southeast Asia isn't known for having the best drivers in the world. I was recently assigned to work in the Philippines for 6 months. My company provided me with a rental car for the duration, and mayhem ensued. Here are some of the things I observed while there. This is part one of a three-part series.
No, I’m not talking about getting on a roundabout, going clockwise, skipping three exits, and getting off where you started. I’m talking about the other kind of u-turn on a roundabout where you go counter-clockwise in a desperate bid to avoid the traffic jam already on the roundabout and succeed in only making said traffic jam worse. If you’re having trouble imagining what I’m talking about because it’s so mind boggling that someone would actually attempt this maneuver, check out the diagram below.
Sure, the highways and main thoroughfares of Luzon (the island Manila is on) have traffic lights. And sure, some of the other street have stop signs. But other than that, nope; the vast majority of intersections in the Philippines have no traffic control devices.
What happens when there's more than one vehicle at an intersection without a traffic control device, you ask? Madness. There's always more than one vehicle at every intersection in the Philippines. It's like the opposite of the Pauli exclusion principle: at least two cars must always be attempting to be in the same place at the same time.
This has resulted in Filipinos developing a unique method for navigating intersections:
Usually this method works pretty well when you consider the circumstances. Sometimes, it doesn't. If you arrange the cars just right, you get gridlock. None of the cars in the intersection can move forward. And since there's so much traffic trying to get through the intersection, no one can back up either. Nightmares are made of this stuff. The picture above wasn't taken in the Philippines, but it gives you an idea of how this works out in practice.
If you're not familiar with jeepneys, here's what they look like:
Yes, that's a typical jeepney. They're usually brightly decorated and have some form of religious statement on them. The Philippines is something like 90% catholic after all.
Jeepneys have two rows of benches in the back facing towards the center line of the jeepney. They can fit ~16 small people in these benches, but when it's rush-hour, that's just not enough. Passengers desperate to get home will hang on to back, sit on the roof, or even the hood of the jeepney. Don't believe me? Proof:
Want to read more about driving in the Philippines? Check out the other two parts of this series:
Photo by Stefan Munder
My desktop recently died on me, so I'm looking to build a new computer. Part of the build includes a USB Wi-Fi adapter. The last Wi-Fi adapter I bought was 802.11g. Since then, 802.11n and 802.11ac have come out and wireless networking has gotten a lot more complicated.
A user reported a connection speed of only 65 Mbps between his laptop and router even though both were advertised to operate at up to 150 Mbps. Why? His laptop can operate a pair of simultaneous 20 MHz streams at 72.2 Mbps each. His router, on the other hand, supports only one stream but with a 40 MHz bandwidth.
This combination is limited to one stream by his router and a maximum channel width of 20 MHz by his laptop. The fastest speed possible with a single 20 MHz channel is 72.2 Mbps when using a short guard interval. Since his setup is running with a long guard interval, the speed is reduced to 65 Mbps.
The take-away is to make sure that you match the number of streams and channel widths between your devices for optimal speed. That doesn't sound too hard, but it is. Manufacturers don't readily advertise that information. Instead they use wonky class designations that are ambiguous and sometimes misleading.
I've bolded the class designations below that I recommend. Products with these class designations are most likely to be 100% compatible with your existing devices and are the least likely to feature proprietary extensions to the 802.11 standards that won't work with devices from other manufacturers. Specifically, these class designations are N600, N900, AC1200, and AC1750. (The N300 designation is generally also free of proprietary extensions, but higher performing N600 routers can be purchased for approximately the same price.)
Decoding the wireless N class designation is pretty simple. See the table below for how D-Link explains wireless N class designations.
Basically, take the number after N, divide by 300, and round down to get the minimum number of streams you have on a given frequency band. (For N750 we have 750/300 = 2.5 → at least 2 streams on the 2.4 GHz and 5 GHz bands.)
If your device is not dual-band, it only operates at 2.4 GHZ or 5 GHz but not both. In this case, use 150 instead of 300 in the calculations above. (For single-band N450 we have 450/150 = 3 → 3 streams.)
These calculations are assuming a 40 MHz channel. This is not always the case as evidenced by the issue at the beginning of this post. For more information, see the chart of 802.11n data rates.
Decoding the meaning of the wireless AC class designations is a bit more difficult. The table below gives my best guess for each term using the standard 802.11ac data rates. Beware that different combinations could be used by manufacturers to get to the same class designation. Always read your device's specifications carefully.
*Proprietary extensions to the 802.11n specification.
**Not widely available as of September, 2014.
Photo by Sean MacEntee
I'm planning a trip to Korea in about a month. An outbreak of MERS started a little over a month ago, so I became concerned that my trip might have to be cancelled. I researched the MERS outbreak in Korea, and I learned about epidemic (or epi) curves.
Epi curves are used by epidemiologists (those who study the patterns, causes, and effects of health and disease conditions in defined populations) to track epidemics. The horizontal axis of an epi curve is time, and the vertical axis is the number of cases confirmed on a particular day.
I found MERS epi curves for Korea on the WHO (World Health Organization) website. You can see the epi curve for Korea and China for June 19 below. The rectangle for May 19 looks a little strange because it shows that there were two newly confirmed cases in Korea and one newly confirmed case in China on that day.
As you can see, the number of MERS cases is declining. I imagine this epi curve is fairly typical for outbreaks of disease. It starts slowly as the index cases infects a few other individuals. There is then a rapid period of growth as the victims infected by the index case infect others. Next, awareness of the epidemic causes health care workers and the general public to take action to quarantine and treat the outbreak. After this, the number of cases slowly declines to zero. I hope Korea will be nearly MERS-free by the time I arrive.
In response to the MERS outbreak, Korea closed hospitals and schools. MERS did not spread outside of hospitals, so schools and kindergartens began reopening.
Photo by Tom Thai
The first step in getting an F-1 student visa is to be accepted by an American school. This can be either a college/university, English-language program, or high school. The process for being accepted into one of these programs is dependent on the program.
Next, your school will give you an I-20 form. Once you have your I-20, you have to gather some other required documents:
Required documents for F-1 visa interview in South Korea
Additionally, there are some recommended documents that you can prepare to make your visa interview easier:
Be prepared to state clearly your educational goals; your major; why you chose that major; why that major is important to your future career in your home country; your graduate school plans, if any; how your degree will help you when you return home.
If you answer the interviewers questions to his/her satisfaction, they will inform you at the end of the interview if you will be receiving a visa or not. If they will not grant you a visa, they will tell you why. You can gather more evidence and schedule another visa interview later to try again. I think that if you fail two interviews that there is a mandatory waiting period of some time before you can have a third interview.
There are a number of misconceptions about 2.4 GHz and 5 GHz Wi-Fi. Let's clear those up.
In the US, the FCC set aside the frequencies 2,400-2,483.5 MHz and 5,150-5,725 MHz for unlicensed broadcasts such as Wi-Fi, cordless phones, etc.* These regions are known as the 2.4 GHz and 5GHz bands, respectively.
The upper frequency of a band minus the lower frequency of a band is the "bandwidth". The bandwidth of a frequency band is directly proportional to the rate at which data can be transmitted. The bandwidth of the 2.4 GHz band is about 80 MHz and the bandwidth of the 5 GHz band is about 570 MHz. Therefore Wi-Fi can transmit data faster on the 5 GHz band because it is wider.
*The ranges given here aren't 100% accurate. The way the FCC splits up the electromagnetic spectrum is complicated.
Microwaves are a huge source of interference for Wi-Fi. Microwaves heat up food by showering it with 2.4 GHz radiation. Some of this radiation leaks out and confuses Wi-Fi receivers when the microwave is running. Cordless phones also often operate on the 2.4 GHz band. The 5 GHz band is used by fewer devices, so the amount of interference on it is less.
The radio engineer formula gives the path loss in db:
where L is the path loss in decibels, d is the distance traveled by the signal, f is the frequency of the signal, and c is the speed of light. Based on this equation, we can expect the path loss to be 20*log10(5/2.4) = 6.3752 dB more for a 5.0 GHZ signal than a 2.4 GHz.
Transmit a pair of signals at 2.4 GHz and 5.0 GHz with 100 mW of transmit power each. If the 2.4 GHz signal received is 10 mW, then the 5 GHz signal will only be 2.304 mW at the same receiver.
Photo by Bill Smith