add device and sigmoid

Signed-off-by: junjie.jiang <junjie.jiang@zilliz.com>

README.md

@@ -36,7 +36,6 @@ DataCollection(p('What is Towhee?',
               ).show()
 ```
 
-<img src="./result.png" height="100px"/>
 
 <br />
 
@@ -56,8 +55,8 @@ Create the operator via the following factory method
 
 ​	***threshold***: float
 
-​    The threshold for filtering with score, defaults to none, i.e., no filtering.
-
+​    The threshold for filtering with score
+   ***device***: str
 <br />
 
 

rerank.py

@@ -1,14 +1,16 @@
 from typing import List
 
+from torch import nn
 from sentence_transformers import CrossEncoder
+
 from towhee.operator import NNOperator
 
 
 class ReRank(NNOperator):
-    def __init__(self, model_name: str = 'cross-encoder/ms-marco-MiniLM-L-6-v2', threshold: float = None):
+    def __init__(self, model_name: str = 'cross-encoder/ms-marco-MiniLM-L-6-v2', threshold: float = 0.6, device: str = None):
         super().__init__()
         self._model_name = model_name
-        self._model = CrossEncoder(self._model_name, max_length=1000)
+        self._model = CrossEncoder(self._model_name, device=device, default_activation_function=nn.Sigmoid())
         self._threshold = threshold
 
     def __call__(self, query: str, docs: List):