What is the principle of Distributed Bragg Reflector (DBR) LDs?
时间: 2024-05-29 07:09:12 浏览: 16
The principle of Distributed Bragg Reflector (DBR) LDs is the use of alternating layers of materials with different refractive indices to form a Bragg grating, which is used to reflect light of a specific wavelength back into the active region of the laser diode. This leads to increased optical gain and improved performance of the laser diode.
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What is mapreduce ? Explain the functions of mapper and reducer with example
MapReduce is a programming model and software framework for processing large sets of data in a distributed and parallel manner. It allows for processing of large data sets on clusters of computers using a simple model for parallel processing.
In the MapReduce framework, the input data is divided into chunks and each chunk is processed by a separate mapper function. The mapper function processes the input data and generates intermediate key-value pairs. These key-value pairs are then sorted and grouped by key, and passed on to the reducer function. The reducer function then aggregates the intermediate key-value pairs and generates a final output.
For example, let's say we have a large data set of customer orders that we want to process using MapReduce. The mapper function will read each order and generate intermediate key-value pairs where the key is the customer ID and the value is the order amount. The intermediate key-value pairs might look like this:
```
customer1: 10.99
customer2: 25.55
customer1: 5.99
customer3: 15.00
customer2: 12.50
```
These intermediate key-value pairs are then sorted and grouped by key:
```
customer1: [10.99, 5.99]
customer2: [25.55, 12.50]
customer3: [15.00]
```
The reducer function then aggregates the values for each key and generates a final output:
```
customer1: 16.98
customer2: 38.05
customer3: 15.00
```
In this example, the MapReduce framework allowed us to process a large data set in a distributed and parallel manner, making it faster and more efficient.
What is the difference between DDOS attack and DOS attack?
DDoS stands for Distributed Denial of Service attack, while DoS stands for Denial of Service attack. The main difference between the two is that a DoS attack is carried out from a single source, whereas a DDoS attack is carried out from multiple sources. In a DoS attack, the attacker floods a network or server with requests, overwhelming its resources and making it unavailable to users. In a DDoS attack, the attacker uses a network of compromised computers (also known as a botnet) to flood the target with requests, making it even harder to mitigate the attack. DDoS attacks are generally more difficult to defend against and can cause more damage than DoS attacks.