How to Buy an iPhone 4 in Urbana-Champaign

I tried finding one, but it took much time more than I expected. Here is some summary that I learned.

- If you place an order on the Apple webpage, it will take 3-4 weeks to get one.

- If you place an order on the AT&T webpage, it will take 1-2 weeks, BUT when I tried, first I got an email that confirms my order and, in a few seconds, got another email that my order has been cancelled without a explicit reason. After experiencing this for three times over five days, I realized that it is not my problem, but AT&T's.

- If you go to the AT&T store in Savoy, you can place an order in store and get one 7-10 days.

- If you have a chance to visit Chicago, you can learn that you can do there whatever you can do in the Savoy AT&T store.

- Best Buy and AT&T store on Marketview Dr., they indeed have some once in a while. But be careful. YOU SHOULD VISIT THE STORES. If you just call them and want to check if they have some iPhones, they may not be honest. Just try to visit those stores on Tuesday & Friday. You can get one easily.

Now I got an iPhone 4.
I actually quite enjoyed hunting it :-)

영작문 교정

On the achievable throughput of CSMA under imperfect carrier sensing
================================================
어드바이중 한분이 제안한것


The main leverage of the algorithms ==> The main idea behind the algorithms
아직 잘 이해가 안감. 굳이 바꿔야 하나...

the Glauber dynamics ==> Glauber dynamics
: Glauber dynamics 자체가 고유명사로 쓰이는 것

very
: 객관적이지 못한 강조는 논문에서 불필요


We first propose a CSMA algorithm, which is named as Preemptive CSMA.
==> We first propose a CSMA algorithm, called Preemptive CSMA.
논문은 짧은 문장을 쓸수록 좋은것 같다.

To gain an insight on the role of ...
==> To gain insight into the role of ...
insight 는 어떤 대상에 into하는 것인가 보다
미국여자분도 지적


This paper is the first work on the characterization of the achievable throughput ...
==> We characterize the achievable throughput ...
말짧게 쓰는 연습 절대적으로 필요...


suggested "such a duration" instead of "such duration,"
BUT duration은 셀수없는 명사임

The model given by (10) is about the false negative event
==> The model in (10) addresses the false negative event
영어 보카가 짧아서 나오는 현상을 고쳐주심

the probability is simplified to ...
==> the probability simplifies as
우리가 수학전개를 했다는 느낌보다는,
이건 이렇게 된다 -- 라는 느낌을 강하게하는 듯

in a second thought ==> on second thought
IDIOM -- 이건 모르면 절대 맞게 쓸수 없는것

Srikant suggested: much larger choices
BUT shouldn't it be "much more choices"??


- 전반적으로 교수님도 사람이라는 생각과
꼼꼼하게 보고 안보고에 따라서 editing 결과가
판이하게 다를수 있다는것


미국 여자분에게 editing을 부탁한것

can achieve the throughput-optimality
optimality가 아직 정의되지 않았기 때문에 the를 붙일수
없는듯==>아님, 계속 the를 지워나갔음.
난 사람들이 다 아는 거기 때문에the를 써야한다고 생각핬음


WiFi, Bluetooth and ZigBee ==> WiFi, Bluetooth, and ZigBee.
코마 미사용! 문장을 연결하는 경우를 제외하고는
마지막에서 두번째 것에는 코마를 안쓰는 줄 알았는데..

<참조 from: http://owl.english.purdue.edu/owl/resource/607/02/>

the throughput loss by carrier sensing
이분은 the쓰는거 참 싫어하시는 듯..
그냥 loss 가 아니라 loss by carrier sensing 이라서 the를
썼으나 필요없는듯

a complete conflict graph, such as a single-cell network.
such 앞의 코마를 써야한다고 지적

CSMA algorithms can achieve the maximum throughput
이해가 안감.. maximum throughput이 한정된 특정
throughput을 가리키기 때문에the를 써야한다고 생각했음

a single channel wireless network  ==> a single-channel wireless network
This graph based model is also ==> This graph-based model is also

wireless network using a graph $G=(V,E)$, where $V$ is the set of nodes
여기서는 where이 conjuction을 위한것이므로
쉬어가기 위해 코마를 써야할듯
==> 모든 equation뒤에 where이 온다면 equation이 코마로
끝나야하나.

The access to the wireless medium is time slotted. ==> Access of the wireless medium is time slotted.


The current transmitting link thus may fill up ==> The current transmitting link may thus fill up
adverb사용 위치는 조동사와 주동사 사이가 맞음

The current transmitting link may thus fill up the slot if it wants to reserve the next one, or  it leaves the last $\alpha$ duration idle.
==> The current transmitting link may thus fill up the slot if it wants to reserve the next one; otherwise it leaves the last $\alpha$ duration idle.
좀더 자연스러운 문장연결 -- 이건 몰라서 못하는것 -_-;


By this ==> In this way
By this는 문어가 아닌듯.. 구어도 아닐수 있음 -_- 몰라

the medium is sensed busy during  ==> the medium is sensed as busy during
busy는 adjective라서 이렇게 써야하는듯

Markov chain would see no change of $a_i$ and $p_i$
==> Markov chain would see no change in $a_i$ and $p_i$

The question on how slowly ==> The question off how slowly

determined by $p_i$ and $a_i$ that may be different across time slots.
==> determined by $p_i$ and $a_i$ which may differ across time slots.

Consider to use a weight ==> Consider use of a weight

provides understanding on how carrier sensing ==> provides understanding of how carrier sensing
The analysis is also the key for the stability proof ==> The analysis is also the key to the stability proof
Interested readers on the topic ==> Interested readers in the topic
This result is against our intuition ==> This result is counter-intuitive

IEEE 802.11n has an energy consumption issue

You can nowadays easily find laptops and routers powered by IEEE 802.11n, which are usually advertised as 5~10x of performance boosters to your wireless network. However, none of smartphones has it. Why is this happening?

As a performance enhancement technology for a physical layer, MIMO has been adopted in IEEE 802.11n, and the standard requires at least two antennas for MIMO operations. This, however, is equivalent to have at least two radio chains, which are in fact the most power-consuming component in a wireless device.

To avoid such an energy issue, an awkward approach is being taken: IEEE 802.11n with single antenna. That will have full MAC layer performance enhancement and part of the physical layer specified by IEEE 802.11n such as 40 MHz channel and higher coding rate, only lacking MIMO part. Broadcom announced this approach at the end of last year:

Excerpted from NETWORKWORLD

(http://www.networkworld.com/news/2008/120808-broadcom-chip.html)

...

The 65-nanometer chip supports 11n in both the 2.4GHz and 5GHz bands, and can run simultaneously in both. Given the constraints of handset size and power, the chip supports only one 11n data stream and one antenna, compared with notebooks or access points that typically support two or possibly three streams, each with a corresponding antenna. The chip's Wi-Fi performance maxes out at 50Mbps of wireless throughput, according to the vendor. That's still nearly twice the throughput of 11a or 11g Wi-Fi.

...

Similarly, Marvell, whose has the only 802.11n products with three spatial streams by three antennas, also announced its new chip-sets that do the same as Broadcom in Jan, 2009:

Excerpted from PCMAG.COM

(http://www.pcmag.com/article2/0,2817,2341375,00.asp)

..

Until now, mobile phones have been stuck at slower 802.11g speeds because 802.11n required chips and antennas that are too large to fit into a mobile-phone form factor. The 1x1 single-stream 802.11n solution can take 802.11n down to a chip as small as 50 mm square, which could easily fit into a phone. That could boost cell-phone Wi-Fi speeds by several times. The 1x1 802.11n chips are available to manufacturers today, he said.

...

This is quite against the communication theory that tells us that even if the total transmit power is fixed, MIMO can give you multiple times of throughput performance. It sounds to me that manufacturing IEEE 802.11n chipsets somehow imposes artificial constraints to the design itself. And this point is where the protocol research should be worked.

Install NX server on Ubuntu Hardy 8.04

NX sever is useful as it can give you secured connection for complete GUI work environment. You can think of this as remote desktop in Windows. This note explains how to install NX server on Ubuntu distribution since the installation instruction provided by NoMachine (here) was not enough for me to quickly have it done.

I suppose that you have one machine running Ubuntu (server) and one another (client) for your daily work running any OS. The following installation instruction is executed in the client machine.

0. Preparation

0.1 You need SSH and SFTP servers running in the server side for installation. Make it sure they are running.

0.2 The installation of NX server requires administratator privilege. You should be able to run "sudo" command with your account.

1. To your local disk, download Debian version of NX client, node and server (you indeed need all at the server side). I'm using NX Free Edition for Linux on http://www.nomachine.com/select-package.php?os=linux&id=1.

2. Upload *.deb packages, which you've just downloaded, to your home directory on the Ubuntu server. You may want to use SFTP client program such as FileZilla (http://filezilla-project.org/) for doing this.

3. Open a SSH session to the server, using any SSH client program such as Putty (http://www.chiark.greenend.org.uk/~sgtatham/putty/). Install the packages that you downloaded by running dpkg utility.

sudo dpkg -i nxclient_X.Y.Z-W_i386.deb

sudo dpkg -i nxnode_3.3.0-17_i386.deb

sudo dpkg -i nxserver_3.3.0-22_i386.deb

You may have some warning for printer configuration file access. I ignored it because I don't need it.

5. Update the configuration file /etc/ssh/sshd_config;

(1) add "nx" to the list of allowed users

AllowUsers thkim rakesh nx

(2) add the next line for NX to get authentication information

AuthorizedKeysFile /usr/NX/home/nx/.ssh/authorized_keys2

If you encounter a problem, see this thread: here.

6. Restart SSH daemon to make the new configuration effective.

sudo /etc/init.d/ssh restart

7. Stop the server (it may have been stopped already) and restart it by running:

sudo /usr/NX/bin/nxserver --stop

sudo /usr/NX/bin/nxserver --start

8. Check the status by:

sudo /usr/NX/bin/nxserver --status

You must be able to see

NX> 900 Connecting to server ...

NX> 110 NX Server is running.

NX> 999 Bye.

It's all done!

Note)

It's possible not to get connected to a machine with a new security key if you have old information about it. In my case when I installed a new server on the machine that had been used as a server with a different OS, I had to delete My Documents/myname/known_host.