CRF and HMM

CRF formulation

• A CRF model consists of
• F = \(<f_1, \ldots, f_k>\), a vector of "feature functions"
• \(\bf{\theta} = <\theta_1, \ldots, \theta_k>\), a vector of weights for each feature function
• Let O = \(<o_1, \ldots, o_T>\) be an observed sequence
• Let A = \(<a_1, \ldots, a_T>\) be the latent variables

$$p(A = y | O) = \frac{\exp (\theta \cdot F(y, O))}{\sum_{y'} \exp (\theta\cdot F(y', O))}$$

Reference

http://knight.cis.temple.edu/~yates/cis8538/sp11/slides/conditional-random-fields.ppt

Sun protection

Sun protection products experience

• Kiehl's Vital Sun Protection: has Avobenzone which can produce radicals under photolysis. But this ingredient is very common in other products that are based on chemical sun projection, like La Roche-Posay sun screen with SPF 60. So far, I quite like Kielh's sun protection products be it the moisturizer with SPF15 or the pure sun screen. The biggest plus of Kiehl's sun screens is that it's not very oily.

How to choose/use sun protection products

• Better to use none oily and nonacnegenic products. 
• Need UVB and UVA broad spectrum protection.
• SPF indicates the time you can stay under the sun without getting a skin burn. Normally it takes 20 minutes to produce redness on a light skinned individual. Multiply this number by the SPF of your product. Example: with an SPF 15 x 20 minutes of sun time = 300 … is how many minutes you can stay in the sun without burning. 300 minutes divided by 1 hour of 60 minutes = 5 hours of sun protection without a sunburn. So SPF 15 seems to be enough for a normal day for sun exposure on the way to work. If you go out during the middle of the day, maybe you can reapply some sun screen. SPF 25 will give 8 hours of sun protection which is enough for a day. 
• The amount to apply is important as well. The SPF is determined based on 2mg/cm^2 usage. This is roughly the size of a coin for face. Japanese brands are usually more liquid, so usually we need 2 times the size of a coin for the face.
• Too much sun screen, can cause burden to the skin as well: clogging the pores if the product is thick and oily. Seems like using moisturizer with SPF 15 is OK in winter and SPF 25 is necessary in the summer. If you are going outdoor for a longer time, use SPF30+.
• Sun screen active ingredients:
• 

Recommended products

• Neutrogena Pure & Free Baby Sunblock Lotion SPF 60+ with PureScreen

婴儿用品，成份属于物理性防晒。通常物理性防晒产品都有过于厚重油腻的嫌疑，是我们综合/油性皮肤的大忌，于是我直接取了一点，抹在我全脸最油腻的地方---鼻子和额头，一开始，感觉很厚很白，就像一般的物理性防晒霜一样。。。心里大叫不好。。。但不出３０秒后，它居然就神奇般的被彻底吸收了，我再摸了摸鼻子和额头，居然比涂抹之前更干爽！而且除了一丝干爽的味道，没有任何异味和油腻的痕迹。但作为一只身经百战的白鼠，我依旧不放心，一直在脸上留了近６个小时，油腻的变化不大，而且摸起来的手感很柔软，我觉得是隔离的作用。再看了看成份表，居然还含有适合敏感肌的燕麦与芦荟，真够有心的～

• La Roche-Posay Anthelios 60 Face Sunscreen

Other resources

http://www.douban.com/note/154595195/

CoffeeScript coding standard

Naming

• Prefixing names with '_' for private methods and member variables.